Add Qt control station source

2026-09-18 16:22:20 +08:00 · 2026-09-18 16:22:20 +08:00 · 90a8434632
commit 90a8434632
parent 8310eecb43
1600 changed files with 364225 additions and 0 deletions
--- a/.gitignore
+++ b/.gitignore
@ -0,0 +1,21 @@
+/.qmake.stash
+/*.pro.user
+/Makefile
+/Makefile.*
+/object_script.*
+/bin/
+/build/
+/build_*/
+/debug/
+/release/
+/dist/
+/third_party/
+/generated_cpp/*
+!/generated_cpp/.gitkeep
+/*.png
+/*.log
+/*.obj
+/*.o
+*.pfx
+*.p12
+*.key
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@ -0,0 +1,199 @@
+cmake_minimum_required(VERSION 3.16)
+project(CmvrControlStation VERSION 1.0.0 LANGUAGES CXX)
+
+set(CMAKE_CXX_STANDARD 14)
+set(CMAKE_CXX_STANDARD_REQUIRED ON)
+set(CMAKE_AUTOMOC ON)
+set(CMAKE_AUTORCC ON)
+set(CMAKE_AUTOUIC ON)
+set(CMAKE_AUTOUIC_SEARCH_PATHS "${CMAKE_CURRENT_SOURCE_DIR}/ui")
+set(CMAKE_INCLUDE_CURRENT_DIR ON)
+
+set(CMVR_INCLUDE_DIR "${CMAKE_CURRENT_SOURCE_DIR}/include")
+set(CMVR_LIB_DIR "${CMAKE_CURRENT_SOURCE_DIR}/lib")
+set(CMVR_TOOLS_DIR "${CMAKE_CURRENT_SOURCE_DIR}/tools")
+set(CMVR_CERT_DIR "${CMAKE_CURRENT_SOURCE_DIR}/certs")
+set(PROTO_ROOT "${CMAKE_CURRENT_SOURCE_DIR}/protos")
+set(GENERATED_ROOT "${CMAKE_CURRENT_BINARY_DIR}/generated_cpp")
+set(PROTOC "${CMVR_TOOLS_DIR}/run_protoc.cmd")
+set(GRPC_CPP_PLUGIN "${CMVR_TOOLS_DIR}/grpc_cpp_plugin.exe")
+
+foreach(REQUIRED_FILE IN ITEMS
+    "${PROTOC}"
+    "${GRPC_CPP_PLUGIN}"
+    "${CMVR_LIB_DIR}/libgrpc++.a"
+    "${CMVR_LIB_DIR}/libprotobuf.a"
+    "${CMVR_LIB_DIR}/libavcodec.dll.a"
+    "${CMVR_LIB_DIR}/liburdfdom_model.dll.a"
+    "${CMVR_LIB_DIR}/msquic.dll")
+    if(NOT EXISTS "${REQUIRED_FILE}")
+        message(FATAL_ERROR "Required local dependency not found: ${REQUIRED_FILE}")
+    endif()
+endforeach()
+
+find_package(Qt5 5.12 REQUIRED COMPONENTS
+    Core Gui Widgets Multimedia 3DCore 3DRender 3DExtras 3DInput)
+
+add_executable(CmvrControlStation WIN32
+    src/audiostreammanager.cpp
+    src/audiostreammanager.h
+    src/configeditorwidget.cpp
+    src/configeditorwidget.h
+    src/main.cpp
+    src/mainwindow.cpp
+    src/mainwindow_ui.cpp
+    src/mainwindow.h
+    src/quictestserver.cpp
+    src/quictestserver.h
+    src/rpcservicewidget.cpp
+    src/rpcservicewidget.h
+    src/robotclient.cpp
+    src/robotclient.h
+    src/trendwidget.cpp
+    src/trendwidget.h
+    src/urdfviewerwidget.cpp
+    src/urdfviewerwidget.h
+    src/videodecoder.cpp
+    src/videodecoder.h
+    ui/mainwindow.ui
+    ui/systemservicepage.ui
+    ui/armservicepage.ui
+    ui/cameraservicepage.ui
+    ui/agvservicepage.ui
+    ui/audioservicepage.ui
+    ui/quicserverpage.ui
+    ui/diagnosticspage.ui
+    ui/rpcservicewidget.ui
+    resources.qrc)
+
+set_target_properties(CmvrControlStation PROPERTIES
+    DEBUG_POSTFIX "_d"
+    RUNTIME_OUTPUT_DIRECTORY "${CMAKE_CURRENT_SOURCE_DIR}/bin/$<LOWER_CASE:$<CONFIG>>")
+
+target_compile_definitions(CmvrControlStation PRIVATE
+    _WIN32_WINNT=0x0600 CMVR_WITH_GRPC=1)
+target_include_directories(CmvrControlStation PRIVATE
+    "${CMVR_INCLUDE_DIR}"
+    "${CMVR_INCLUDE_DIR}/urdfdom_headers"
+    "${GENERATED_ROOT}")
+target_link_libraries(CmvrControlStation PRIVATE
+    Qt5::Core Qt5::Gui Qt5::Widgets Qt5::Multimedia
+    Qt5::3DCore Qt5::3DRender Qt5::3DExtras Qt5::3DInput)
+
+set(PROTO_NAMES
+    cmvr/api/common
+    cmvr/msgs/agv
+    cmvr/api/agv_command
+    cmvr/api/agv_service
+    cmvr/api/arm_command
+    cmvr/api/arm_service
+    cmvr/api/biohead_command
+    cmvr/api/biohead_service
+    cmvr/api/camera_command
+    cmvr/api/camera_service
+    cmvr/api/configuration_command
+    cmvr/api/configuration_service
+    cmvr/api/dexhand_command
+    cmvr/api/dexhand_service
+    cmvr/api/hlc_command
+    cmvr/api/hlc_service
+    cmvr/api/microphone_command
+    cmvr/api/microphone_service
+    cmvr/api/speaker_command
+    cmvr/api/speaker_service
+    cmvr/api/system_command
+    cmvr/api/system_service
+    cmvr/api/test_service
+    cmvr/quic_edge/v1/quic_edge)
+set(SERVICE_NAMES
+    cmvr/api/agv_service
+    cmvr/api/arm_service
+    cmvr/api/biohead_service
+    cmvr/api/camera_service
+    cmvr/api/configuration_service
+    cmvr/api/dexhand_service
+    cmvr/api/hlc_service
+    cmvr/api/microphone_service
+    cmvr/api/speaker_service
+    cmvr/api/system_service
+    cmvr/api/test_service)
+
+set(GENERATED_FILES)
+foreach(PROTO_NAME IN LISTS PROTO_NAMES)
+    set(PROTO_FILE "${PROTO_ROOT}/${PROTO_NAME}.proto")
+    set(PB_CC "${GENERATED_ROOT}/${PROTO_NAME}.pb.cc")
+    set(PB_H "${GENERATED_ROOT}/${PROTO_NAME}.pb.h")
+    get_filename_component(PROTO_OUTPUT_DIR "${PB_CC}" DIRECTORY)
+    add_custom_command(
+        OUTPUT "${PB_CC}" "${PB_H}"
+        COMMAND ${CMAKE_COMMAND} -E make_directory "${PROTO_OUTPUT_DIR}"
+        COMMAND "${PROTOC}"
+            --proto_path="${PROTO_ROOT}"
+            --cpp_out="${GENERATED_ROOT}"
+            "${PROTO_FILE}"
+        DEPENDS "${PROTO_FILE}" "${PROTOC}"
+        VERBATIM)
+    list(APPEND GENERATED_FILES "${PB_CC}" "${PB_H}")
+endforeach()
+
+foreach(SERVICE_NAME IN LISTS SERVICE_NAMES)
+    set(PROTO_FILE "${PROTO_ROOT}/${SERVICE_NAME}.proto")
+    set(GRPC_CC "${GENERATED_ROOT}/${SERVICE_NAME}.grpc.pb.cc")
+    set(GRPC_H "${GENERATED_ROOT}/${SERVICE_NAME}.grpc.pb.h")
+    get_filename_component(PROTO_OUTPUT_DIR "${GRPC_CC}" DIRECTORY)
+    add_custom_command(
+        OUTPUT "${GRPC_CC}" "${GRPC_H}"
+        COMMAND ${CMAKE_COMMAND} -E make_directory "${PROTO_OUTPUT_DIR}"
+        COMMAND "${PROTOC}"
+            --proto_path="${PROTO_ROOT}"
+            --grpc_out="${GENERATED_ROOT}"
+            --plugin=protoc-gen-grpc="${GRPC_CPP_PLUGIN}"
+            "${PROTO_FILE}"
+        DEPENDS "${PROTO_FILE}" "${PROTOC}" "${GRPC_CPP_PLUGIN}"
+        VERBATIM)
+    list(APPEND GENERATED_FILES "${GRPC_CC}" "${GRPC_H}")
+endforeach()
+target_sources(CmvrControlStation PRIVATE ${GENERATED_FILES})
+
+file(GLOB ABSL_STATIC_LIBS "${CMVR_LIB_DIR}/libabsl_*.a")
+target_link_libraries(CmvrControlStation PRIVATE
+    "-Wl,--start-group"
+    "${CMVR_LIB_DIR}/libgrpc++.a"
+    "${CMVR_LIB_DIR}/libgrpc.a"
+    "${CMVR_LIB_DIR}/libgpr.a"
+    "${CMVR_LIB_DIR}/libaddress_sorting.a"
+    "${CMVR_LIB_DIR}/libre2.a"
+    "${CMVR_LIB_DIR}/libupb.a"
+    "${CMVR_LIB_DIR}/libcares.a"
+    "${CMVR_LIB_DIR}/libssl.a"
+    "${CMVR_LIB_DIR}/libcrypto.a"
+    "${CMVR_LIB_DIR}/libzlibstatic.a"
+    "${CMVR_LIB_DIR}/libprotobuf.a"
+    ${ABSL_STATIC_LIBS}
+    "-Wl,--end-group"
+    "${CMVR_LIB_DIR}/libavcodec.dll.a"
+    "${CMVR_LIB_DIR}/libavutil.dll.a"
+    "${CMVR_LIB_DIR}/libswscale.dll.a"
+    "${CMVR_LIB_DIR}/liburdfdom_model.dll.a"
+    ws2_32 crypt32 advapi32 bcrypt dbghelp iphlpapi secur32 ntdll)
+
+file(GLOB CMVR_RUNTIME_DLLS "${CMVR_LIB_DIR}/*.dll")
+foreach(RUNTIME_DLL IN LISTS CMVR_RUNTIME_DLLS)
+    add_custom_command(TARGET CmvrControlStation POST_BUILD
+        COMMAND ${CMAKE_COMMAND} -E copy_if_different
+            "${RUNTIME_DLL}" "$<TARGET_FILE_DIR:CmvrControlStation>")
+endforeach()
+foreach(CERTIFICATE IN ITEMS quic-test-server.pfx quic-test-ca.crt)
+    add_custom_command(TARGET CmvrControlStation POST_BUILD
+        COMMAND ${CMAKE_COMMAND} -E copy_if_different
+            "${CMVR_CERT_DIR}/${CERTIFICATE}"
+            "$<TARGET_FILE_DIR:CmvrControlStation>/${CERTIFICATE}")
+endforeach()
+add_custom_command(TARGET CmvrControlStation POST_BUILD
+    COMMAND ${CMAKE_COMMAND} -E make_directory
+        "$<TARGET_FILE_DIR:CmvrControlStation>/models"
+    COMMAND ${CMAKE_COMMAND} -E copy_if_different
+        "${CMAKE_CURRENT_SOURCE_DIR}/models/demo_arm.urdf"
+        "$<TARGET_FILE_DIR:CmvrControlStation>/models/demo_arm.urdf")
+
+install(TARGETS CmvrControlStation RUNTIME DESTINATION bin)
--- a/CmvrControlStation.pro
+++ b/CmvrControlStation.pro
@ -0,0 +1,301 @@
+QT += core gui widgets multimedia 3dcore 3drender 3dextras 3dinput
+
+CONFIG += c++14 warn_on debug_and_release
+TEMPLATE = app
+
+DEFINES += QT_DEPRECATED_WARNINGS _WIN32_WINNT=0x0600
+
+INCLUDE_DIR = $$clean_path($$PWD/include)
+LIB_DIR = $$clean_path($$PWD/lib)
+TOOLS_DIR = $$clean_path($$PWD/tools)
+CERT_DIR = $$clean_path($$PWD/certs)
+PROTO_ROOT = $$clean_path($$PWD/protos)
+PROTO_GEN_DIR = $$clean_path($$PWD/generated_cpp)
+PROTOC = $$TOOLS_DIR/run_protoc.cmd
+GRPC_CPP_PLUGIN = $$TOOLS_DIR/grpc_cpp_plugin.exe
+MSQUIC_DLL = $$LIB_DIR/msquic.dll
+MSQUIC_TEST_CERT = $$CERT_DIR/quic-test-server.pfx
+MSQUIC_TEST_CA = $$CERT_DIR/quic-test-ca.crt
+RUNTIME_DLLS = $$files($$LIB_DIR/*.dll)
+DEMO_URDF = $$clean_path($$PWD/models/demo_arm.urdf)
+QT_SCENEPARSER_DIR = $$clean_path($$[QT_INSTALL_PLUGINS]/sceneparsers)
+
+!exists($$PROTOC): error("protoc launcher not found. Run scripts/build_native_deps.ps1 first.")
+!exists($$GRPC_CPP_PLUGIN): error("grpc_cpp_plugin.exe not found. Run scripts/build_native_deps.ps1 first.")
+!exists($$MSQUIC_DLL): error("msquic.dll not found. Run scripts/install_msquic.ps1 first.")
+!exists($$MSQUIC_TEST_CERT): error("QUIC test certificate not found. Run scripts/install_msquic.ps1 first.")
+!exists($$MSQUIC_TEST_CA): error("QUIC test CA not found. Run scripts/install_msquic.ps1 first.")
+!exists($$INCLUDE_DIR/libavcodec/avcodec.h): error("FFmpeg headers not found in include.")
+!exists($$LIB_DIR/avcodec-58.dll): error("FFmpeg runtime DLLs not found in lib.")
+!exists($$INCLUDE_DIR/urdf_parser/urdf_parser.h): error("urdfdom headers not found in include.")
+!exists($$LIB_DIR/liburdfdom_model.dll.a): error("urdfdom link library not found in lib.")
+!exists($$LIB_DIR/liburdfdom_model.dll): error("urdfdom runtime DLL not found in lib.")
+
+PROTO_FILES = \
+    $$PROTO_ROOT/cmvr/api/common.proto \
+    $$PROTO_ROOT/cmvr/api/agv_command.proto \
+    $$PROTO_ROOT/cmvr/api/agv_service.proto \
+    $$PROTO_ROOT/cmvr/api/arm_command.proto \
+    $$PROTO_ROOT/cmvr/api/arm_service.proto \
+    $$PROTO_ROOT/cmvr/api/biohead_command.proto \
+    $$PROTO_ROOT/cmvr/api/biohead_service.proto \
+    $$PROTO_ROOT/cmvr/api/camera_command.proto \
+    $$PROTO_ROOT/cmvr/api/camera_service.proto \
+    $$PROTO_ROOT/cmvr/api/configuration_command.proto \
+    $$PROTO_ROOT/cmvr/api/configuration_service.proto \
+    $$PROTO_ROOT/cmvr/api/dexhand_command.proto \
+    $$PROTO_ROOT/cmvr/api/dexhand_service.proto \
+    $$PROTO_ROOT/cmvr/api/hlc_command.proto \
+    $$PROTO_ROOT/cmvr/api/hlc_service.proto \
+    $$PROTO_ROOT/cmvr/api/microphone_command.proto \
+    $$PROTO_ROOT/cmvr/api/microphone_service.proto \
+    $$PROTO_ROOT/cmvr/api/speaker_command.proto \
+    $$PROTO_ROOT/cmvr/api/speaker_service.proto \
+    $$PROTO_ROOT/cmvr/api/system_command.proto \
+    $$PROTO_ROOT/cmvr/api/system_service.proto \
+    $$PROTO_ROOT/cmvr/api/test_service.proto
+
+GRPC_PROTO_FILES = \
+    $$PROTO_ROOT/cmvr/api/agv_service.proto \
+    $$PROTO_ROOT/cmvr/api/arm_service.proto \
+    $$PROTO_ROOT/cmvr/api/biohead_service.proto \
+    $$PROTO_ROOT/cmvr/api/camera_service.proto \
+    $$PROTO_ROOT/cmvr/api/configuration_service.proto \
+    $$PROTO_ROOT/cmvr/api/dexhand_service.proto \
+    $$PROTO_ROOT/cmvr/api/hlc_service.proto \
+    $$PROTO_ROOT/cmvr/api/microphone_service.proto \
+    $$PROTO_ROOT/cmvr/api/speaker_service.proto \
+    $$PROTO_ROOT/cmvr/api/system_service.proto \
+    $$PROTO_ROOT/cmvr/api/test_service.proto
+
+MSG_PROTO_FILES = \
+    $$PROTO_ROOT/cmvr/msgs/agv.proto
+
+CONFIG_PROTO_FILES = \
+    $$PROTO_ROOT/cmvr/config/agv_config/agv_config.proto \
+    $$PROTO_ROOT/cmvr/config/arm_config/arm_config.proto \
+    $$PROTO_ROOT/cmvr/config/aubo_robot_config/aubo_robot_config.proto \
+    $$PROTO_ROOT/cmvr/config/biohead_config/biohead_config.proto \
+    $$PROTO_ROOT/cmvr/config/camera_config/camera_config.proto \
+    $$PROTO_ROOT/cmvr/config/cmvr_es_config/cmvr_es_config.proto \
+    $$PROTO_ROOT/cmvr/config/device_manager_config/device_manager_config.proto \
+    $$PROTO_ROOT/cmvr/config/dexhand_config/dexhand_config.proto \
+    $$PROTO_ROOT/cmvr/config/grpc_server_config/grpc_server_config.proto \
+    $$PROTO_ROOT/cmvr/config/logger_config/logger_config.proto \
+    $$PROTO_ROOT/cmvr/config/microphone_config/microphone_config.proto \
+    $$PROTO_ROOT/cmvr/config/motor_config/motor_config.proto \
+    $$PROTO_ROOT/cmvr/config/quic_edge_config/quic_edge_config.proto \
+    $$PROTO_ROOT/cmvr/config/self_collision_task_config/self_collision_task_config.proto \
+    $$PROTO_ROOT/cmvr/config/speaker_config/speaker_config.proto \
+    $$PROTO_ROOT/cmvr/config/task_manager_config/task_manager_config.proto \
+    $$PROTO_ROOT/cmvr/config/touch_screen_task_config/touch_screen_task_config.proto
+
+CONFIG_ROOT_PROTO_FILES = \
+    $$PROTO_ROOT/cmvr/config/cartesian_motion_validation_config.proto \
+    $$PROTO_ROOT/cmvr/config/joint_limits_config.proto \
+    $$PROTO_ROOT/cmvr/config/lawba_ik_config.proto \
+    $$PROTO_ROOT/cmvr/config/pinocchio_dls_ik_config.proto \
+    $$PROTO_ROOT/cmvr/config/pinocchio_qp_ik_config.proto \
+    $$PROTO_ROOT/cmvr/config/srs_ik_config.proto \
+    $$PROTO_ROOT/cmvr/config/touch_screen_algorithm_config.proto \
+    $$PROTO_ROOT/cmvr/config/touch_screen_common_config.proto
+
+COMMON_PROTO_FILES = \
+    $$PROTO_ROOT/cmvr/common/geometry.proto
+
+MUJOCO_PROTO_FILES = \
+    $$PROTO_ROOT/cmvr/config/mujoco_config/mujoco_world_config.proto
+
+QUIC_PROTO_FILES = \
+    $$PROTO_ROOT/cmvr/quic_edge/v1/quic_edge.proto
+
+# Show the complete local proto tree in Qt Creator without compiling unused APIs.
+OTHER_FILES += $$files($$PROTO_ROOT/*.proto, true) $$DEMO_URDF
+
+INCLUDEPATH += \
+    $$PROTO_GEN_DIR \
+    $$INCLUDE_DIR \
+    $$INCLUDE_DIR/urdfdom_headers
+
+protobuf_compiler.name = Protobuf ${QMAKE_FILE_IN}
+protobuf_compiler.input = PROTO_FILES
+protobuf_compiler.output = $$PROTO_GEN_DIR/cmvr/api/${QMAKE_FILE_BASE}.pb.cc
+protobuf_compiler.commands = $$quote($$PROTOC) --proto_path=$$quote($$PROTO_ROOT) --cpp_out=$$quote($$PROTO_GEN_DIR) $$quote($$PROTO_ROOT/cmvr/api/${QMAKE_FILE_BASE}.proto)
+protobuf_compiler.depends = $$PROTO_FILES $$MSG_PROTO_FILES
+protobuf_compiler.variable_out = SOURCES
+protobuf_compiler.CONFIG += target_predeps
+
+msg_protobuf_compiler.name = Protobuf ${QMAKE_FILE_IN}
+msg_protobuf_compiler.input = MSG_PROTO_FILES
+msg_protobuf_compiler.output = $$PROTO_GEN_DIR/cmvr/msgs/${QMAKE_FILE_BASE}.pb.cc
+msg_protobuf_compiler.commands = $$quote($$PROTOC) --proto_path=$$quote($$PROTO_ROOT) --cpp_out=$$quote($$PROTO_GEN_DIR) $$quote($$PROTO_ROOT/cmvr/msgs/${QMAKE_FILE_BASE}.proto)
+msg_protobuf_compiler.depends = $$MSG_PROTO_FILES
+msg_protobuf_compiler.variable_out = SOURCES
+msg_protobuf_compiler.CONFIG += target_predeps
+
+config_protobuf_compiler.name = Protobuf ${QMAKE_FILE_IN}
+config_protobuf_compiler.input = CONFIG_PROTO_FILES
+config_protobuf_compiler.output = $$PROTO_GEN_DIR/cmvr/config/${QMAKE_FILE_BASE}/${QMAKE_FILE_BASE}.pb.cc
+config_protobuf_compiler.commands = $$quote($$PROTOC) --proto_path=$$quote($$PROTO_ROOT) --cpp_out=$$quote($$PROTO_GEN_DIR) $$quote($$PWD/${QMAKE_FILE_IN})
+config_protobuf_compiler.depends = $$CONFIG_PROTO_FILES
+config_protobuf_compiler.variable_out = SOURCES
+config_protobuf_compiler.CONFIG += target_predeps
+
+config_root_protobuf_compiler.name = Protobuf ${QMAKE_FILE_IN}
+config_root_protobuf_compiler.input = CONFIG_ROOT_PROTO_FILES
+config_root_protobuf_compiler.output = $$PROTO_GEN_DIR/cmvr/config/${QMAKE_FILE_BASE}.pb.cc
+config_root_protobuf_compiler.commands = $$quote($$PROTOC) --proto_path=$$quote($$PROTO_ROOT) --cpp_out=$$quote($$PROTO_GEN_DIR) $$quote($$PWD/${QMAKE_FILE_IN})
+config_root_protobuf_compiler.depends = $$CONFIG_ROOT_PROTO_FILES $$COMMON_PROTO_FILES
+config_root_protobuf_compiler.variable_out = SOURCES
+config_root_protobuf_compiler.CONFIG += target_predeps
+
+common_protobuf_compiler.name = Protobuf ${QMAKE_FILE_IN}
+common_protobuf_compiler.input = COMMON_PROTO_FILES
+common_protobuf_compiler.output = $$PROTO_GEN_DIR/cmvr/common/${QMAKE_FILE_BASE}.pb.cc
+common_protobuf_compiler.commands = $$quote($$PROTOC) --proto_path=$$quote($$PROTO_ROOT) --cpp_out=$$quote($$PROTO_GEN_DIR) $$quote($$PWD/${QMAKE_FILE_IN})
+common_protobuf_compiler.depends = $$COMMON_PROTO_FILES
+common_protobuf_compiler.variable_out = SOURCES
+common_protobuf_compiler.CONFIG += target_predeps
+
+mujoco_protobuf_compiler.name = Protobuf ${QMAKE_FILE_IN}
+mujoco_protobuf_compiler.input = MUJOCO_PROTO_FILES
+mujoco_protobuf_compiler.output = $$PROTO_GEN_DIR/cmvr/config/mujoco_config/${QMAKE_FILE_BASE}.pb.cc
+mujoco_protobuf_compiler.commands = $$quote($$PROTOC) --proto_path=$$quote($$PROTO_ROOT) --cpp_out=$$quote($$PROTO_GEN_DIR) $$quote($$PWD/${QMAKE_FILE_IN})
+mujoco_protobuf_compiler.depends = $$MUJOCO_PROTO_FILES
+mujoco_protobuf_compiler.variable_out = SOURCES
+mujoco_protobuf_compiler.CONFIG += target_predeps
+
+grpc_compiler.name = gRPC ${QMAKE_FILE_IN}
+grpc_compiler.input = GRPC_PROTO_FILES
+grpc_compiler.output = $$PROTO_GEN_DIR/cmvr/api/${QMAKE_FILE_BASE}.grpc.pb.cc
+grpc_compiler.commands = $$quote($$PROTOC) --proto_path=$$quote($$PROTO_ROOT) --grpc_out=$$quote($$PROTO_GEN_DIR) --plugin=protoc-gen-grpc=$$quote($$GRPC_CPP_PLUGIN) $$quote($$PROTO_ROOT/cmvr/api/${QMAKE_FILE_BASE}.proto)
+grpc_compiler.depends = $$PROTO_FILES $$MSG_PROTO_FILES
+grpc_compiler.variable_out = SOURCES
+grpc_compiler.CONFIG += target_predeps
+
+quic_protobuf_compiler.name = Protobuf ${QMAKE_FILE_IN}
+quic_protobuf_compiler.input = QUIC_PROTO_FILES
+quic_protobuf_compiler.output = $$PROTO_GEN_DIR/cmvr/quic_edge/v1/${QMAKE_FILE_BASE}.pb.cc
+quic_protobuf_compiler.commands = $$quote($$PROTOC) --proto_path=$$quote($$PROTO_ROOT) --cpp_out=$$quote($$PROTO_GEN_DIR) $$quote($$PROTO_ROOT/cmvr/quic_edge/v1/${QMAKE_FILE_BASE}.proto)
+quic_protobuf_compiler.depends = $$QUIC_PROTO_FILES
+quic_protobuf_compiler.variable_out = SOURCES
+quic_protobuf_compiler.CONFIG += target_predeps
+
+QMAKE_EXTRA_COMPILERS += protobuf_compiler msg_protobuf_compiler config_protobuf_compiler config_root_protobuf_compiler common_protobuf_compiler mujoco_protobuf_compiler grpc_compiler quic_protobuf_compiler
+
+ABSL_STATIC_LIBS = $$files($$LIB_DIR/libabsl_*.a)
+LIBS += \
+    -Wl,--start-group \
+    $$LIB_DIR/libgrpc++.a \
+    $$LIB_DIR/libgrpc.a \
+    $$LIB_DIR/libgpr.a \
+    $$LIB_DIR/libaddress_sorting.a \
+    $$LIB_DIR/libre2.a \
+    $$LIB_DIR/libupb.a \
+    $$LIB_DIR/libcares.a \
+    $$LIB_DIR/libssl.a \
+    $$LIB_DIR/libcrypto.a \
+    $$LIB_DIR/libzlibstatic.a \
+    $$LIB_DIR/libprotobuf.a \
+    $$ABSL_STATIC_LIBS \
+    -Wl,--end-group \
+    $$LIB_DIR/libavcodec.dll.a \
+    $$LIB_DIR/libavutil.dll.a \
+    $$LIB_DIR/libswscale.dll.a \
+    $$LIB_DIR/liburdfdom_model.dll.a \
+    -lws2_32 \
+    -lcrypt32 \
+    -ladvapi32 \
+    -lbcrypt \
+    -ldbghelp \
+    -liphlpapi \
+    -lsecur32 \
+    -lntdll
+
+DEFINES += CMVR_WITH_GRPC=1
+
+CONFIG(debug, debug|release) {
+    TARGET = CmvrControlStation_d
+    DESTDIR = $$clean_path($$PWD/bin/debug)
+    OBJECTS_DIR = build/debug/obj
+    MOC_DIR = build/debug/moc
+    RCC_DIR = build/debug/rcc
+    UI_DIR = build/debug/ui
+    DEFINES += CMVR_DEBUG_BUILD
+    ASSIMP_SCENE_PARSER = $$QT_SCENEPARSER_DIR/assimpsceneimportd.dll
+} else {
+    TARGET = CmvrControlStation
+    DESTDIR = $$clean_path($$PWD/bin/release)
+    OBJECTS_DIR = build/release/obj
+    MOC_DIR = build/release/moc
+    RCC_DIR = build/release/rcc
+    UI_DIR = build/release/ui
+    DEFINES += NDEBUG
+    ASSIMP_SCENE_PARSER = $$QT_SCENEPARSER_DIR/assimpsceneimport.dll
+}
+
+!exists($$ASSIMP_SCENE_PARSER): error("Qt3D Assimp scene parser not found in the selected Qt Kit.")
+
+SOURCES += \
+    src/audiostreammanager.cpp \
+    src/configeditorwidget.cpp \
+    src/main.cpp \
+    src/mainwindow.cpp \
+    src/mainwindow_ui.cpp \
+    src/quictestserver.cpp \
+    src/rpcservicewidget.cpp \
+    src/robotclient.cpp \
+    src/trendwidget.cpp \
+    src/urdfviewerwidget.cpp \
+    src/videodecoder.cpp \
+    src/videorenderwidget.cpp \
+    ui/handeyecalibrationwidget.cpp
+
+HEADERS += \
+    src/audiostreammanager.h \
+    src/configeditorwidget.h \
+    src/mainwindow.h \
+    src/quictestserver.h \
+    src/rpcservicewidget.h \
+    src/robotclient.h \
+    src/trendwidget.h \
+    src/uiicons.h \
+    src/urdfviewerwidget.h \
+    src/videodecoder.h \
+    src/videoframe.h \
+    src/videorenderwidget.h \
+    ui/handeyecalibrationwidget.h
+
+FORMS += \
+    ui/handeyecalibrationwidget.ui \
+    ui/mainwindow.ui \
+    ui/systemservicepage.ui \
+    ui/armservicepage.ui \
+    ui/cameraservicepage.ui \
+    ui/agvservicepage.ui \
+    ui/agvstatusdialog.ui \
+    ui/audioservicepage.ui \
+    ui/quicserverpage.ui \
+    ui/diagnosticspage.ui \
+    ui/rpcservicewidget.ui
+
+RESOURCES += resources.qrc
+
+runtime_library_deployment.files = $$RUNTIME_DLLS
+runtime_library_deployment.path = $$DESTDIR
+quic_certificate_deployment.files = $$MSQUIC_TEST_CERT
+quic_certificate_deployment.path = $$DESTDIR
+quic_ca_deployment.files = $$MSQUIC_TEST_CA
+quic_ca_deployment.path = $$DESTDIR
+demo_urdf_deployment.files = $$DEMO_URDF
+demo_urdf_deployment.path = $$DESTDIR/models
+assimp_scene_parser_deployment.files = $$ASSIMP_SCENE_PARSER
+assimp_scene_parser_deployment.path = $$DESTDIR/sceneparsers
+COPIES += runtime_library_deployment quic_certificate_deployment quic_ca_deployment demo_urdf_deployment assimp_scene_parser_deployment
+
+win32 {
+    QMAKE_POST_LINK += $$QMAKE_COPY_FILE $$shell_quote($$shell_path($$MSQUIC_TEST_CERT)) $$shell_quote($$shell_path($$DESTDIR/quic-test-server.pfx))
+    QMAKE_POST_LINK += $$escape_expand(\n\t) $$QMAKE_COPY_FILE $$shell_quote($$shell_path($$MSQUIC_TEST_CA)) $$shell_quote($$shell_path($$DESTDIR/quic-test-ca.crt))
+}
+
+win32:RC_ICONS =
--- a/NATIVE_DEPS.md
+++ b/NATIVE_DEPS.md
@ -0,0 +1,85 @@
+# Windows native dependencies
+
+The project uses Qt 5.12.4 with its 64-bit MinGW 7.3 kit:
+
+- Qt: `C:\Qt\Qt5.12.4\5.12.4\mingw73_64`
+- Compiler: `C:\Qt\Qt5.12.4\Tools\mingw730_64`
+- gRPC 1.48.4 and Protobuf 3.19.5
+- FFmpeg 4.4.5 with H.264, H.265/HEVC and MJPEG decoders
+- MsQuic 2.5.9 OpenSSL x64
+- urdfdom 4.0.3
+
+Do not use an MSVC, 32-bit, or different MinGW kit. The native libraries in
+`lib` use the Qt MinGW 7.3 64-bit ABI.
+
+## Project layout
+
+The application build has no dependency on `third_party/install`:
+
+```text
+include/  dependency headers
+lib/      static libraries, import libraries and runtime DLLs
+tools/    protoc.exe, grpc_cpp_plugin.exe and the protoc launcher
+certs/    QUIC test certificate and CA
+```
+
+Both qmake and CMake link only from `lib`. qmake copies every `lib/*.dll` into
+the selected executable directory (`bin/debug` or `bin/release`) during the
+build. QUIC certificates and the demo URDF are deployed beside the executable
+at the same time.
+
+`tools/run_protoc.cmd` adds `lib` to the proto compiler process PATH. This lets
+`protoc.exe` and `grpc_cpp_plugin.exe` load their MinGW runtime DLLs without
+duplicating DLL files under `tools`.
+
+## Rebuilding dependencies
+
+The checked-in `include`, `lib`, `tools`, and `certs` directories are enough to
+build the application. To rebuild all native dependencies from source, run:
+
+```powershell
+powershell -ExecutionPolicy Bypass -File .\scripts\build_native_deps.ps1 -Jobs 4
+```
+
+The script creates a temporary `third_party` download/build/install tree and
+then runs `scripts/stage_native_deps.ps1` to refresh the four project
+directories above. `third_party` is ignored and can be removed after staging.
+
+To refresh only the staged files from an existing install tree:
+
+```powershell
+powershell -ExecutionPolicy Bypass -File .\scripts\stage_native_deps.ps1
+```
+
+## Qt Creator
+
+Open `CmvrControlStation.pro`, select the Desktop Qt 5.12.4 MinGW 64-bit kit,
+run qmake, and then rebuild. Debug and Release are kept separate:
+
+```text
+bin/debug/CmvrControlStation_d.exe
+bin/release/CmvrControlStation.exe
+```
+
+Proto sources are read from the project-local `protos` directory and generated
+under `generated_cpp`. No file from `cmvr-es` or another source repository is
+required during compilation.
+
+## QUIC certificate
+
+To generate a test server certificate containing the machine LAN address:
+
+```powershell
+.\scripts\install_msquic.ps1 -ServerIp 192.168.0.118
+.\scripts\stage_native_deps.ps1
+```
+
+The client must trust `certs/quic-test-ca.crt`. The PFX password is
+`cmvr-test`.
+
+## Application deployment
+
+The `.pro` file deploys native DLLs maintained in `lib`, including FFmpeg,
+MsQuic, urdfdom, zlib, and the MinGW runtime. Qt framework DLLs and Qt plugins
+remain owned by the selected Qt kit; use `windeployqt` when producing a
+standalone distribution outside Qt Creator.
--- a/certs/quic-test-ca.crt
+++ b/certs/quic-test-ca.crt
@ -0,0 +1,25 @@
+-----BEGIN CERTIFICATE-----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+-----END CERTIFICATE-----
--- a/generated_cpp/.gitkeep
+++ b/generated_cpp/.gitkeep
@ -0,0 +1 @@
+
--- a/icons/activity.svg
+++ b/icons/activity.svg
@ -0,0 +1,2 @@
+<!-- Lucide activity, ISC license -->
+<svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24" fill="none" stroke="#000" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><path d="M22 12h-2.48a2 2 0 0 0-1.93 1.46l-2.35 8.36a.25.25 0 0 1-.48 0L9.24 2.18a.25.25 0 0 0-.48 0l-2.35 8.36A2 2 0 0 1 4.49 12H2"/></svg>
--- a/icons/bot.svg
+++ b/icons/bot.svg
@ -0,0 +1,2 @@
+<!-- Lucide bot, ISC license -->
+<svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24" fill="none" stroke="#000" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><path d="M12 8V4H8"/><rect width="16" height="12" x="4" y="8" rx="2"/><path d="M2 14h2M20 14h2M15 13v2M9 13v2"/></svg>
--- a/icons/braces.svg
+++ b/icons/braces.svg
@ -0,0 +1,2 @@
+<!-- Lucide braces, ISC license -->
+<svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24" fill="none" stroke="#000" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><path d="M8 3H7a2 2 0 0 0-2 2v5a2 2 0 0 1-2 2 2 2 0 0 1 2 2v5c0 1.1.9 2 2 2h1M16 21h1a2 2 0 0 0 2-2v-5c0-1.1.9-2 2-2a2 2 0 0 1-2-2V5a2 2 0 0 0-2-2h-1"/></svg>
--- a/icons/camera.svg
+++ b/icons/camera.svg
@ -0,0 +1,2 @@
+<!-- Lucide camera, ISC license -->
+<svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24" fill="none" stroke="#000" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><path d="M14.5 4h-5L7 7H4a2 2 0 0 0-2 2v9a2 2 0 0 0 2 2h16a2 2 0 0 0 2-2V9a2 2 0 0 0-2-2h-3l-2.5-3z"/><circle cx="12" cy="13" r="3"/></svg>
--- a/icons/check.svg
+++ b/icons/check.svg
@ -0,0 +1,2 @@
+<!-- Lucide check, ISC license -->
+<svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24" fill="none" stroke="#fff" stroke-width="3" stroke-linecap="round" stroke-linejoin="round"><path d="M20 6 9 17l-5-5"/></svg>
--- a/icons/chevron-down.svg
+++ b/icons/chevron-down.svg
@ -0,0 +1,2 @@
+<!-- Lucide chevron-down, ISC license -->
+<svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24" fill="none" stroke="#66727d" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><path d="m6 9 6 6 6-6"/></svg>
--- a/icons/chevron-up.svg
+++ b/icons/chevron-up.svg
@ -0,0 +1,2 @@
+<!-- Lucide chevron-up, ISC license -->
+<svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24" fill="none" stroke="#66727d" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><path d="m18 15-6-6-6 6"/></svg>
--- a/icons/copy.svg
+++ b/icons/copy.svg
@ -0,0 +1,2 @@
+<!-- Lucide copy, ISC license -->
+<svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24" fill="none" stroke="#000" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><rect width="14" height="14" x="8" y="8" rx="2" ry="2"/><path d="M4 16c-1.1 0-2-.9-2-2V4c0-1.1.9-2 2-2h10c1.1 0 2 .9 2 2"/></svg>
--- a/icons/crosshair.svg
+++ b/icons/crosshair.svg
@ -0,0 +1,2 @@
+<!-- Lucide crosshair, ISC license -->
+<svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24" fill="none" stroke="#000" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><circle cx="12" cy="12" r="10"/><path d="M22 12h-4M6 12H2M12 6V2M12 22v-4"/></svg>
--- a/icons/folder-open.svg
+++ b/icons/folder-open.svg
@ -0,0 +1,2 @@
+<!-- Lucide folder-open, ISC license -->
+<svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24" fill="none" stroke="#000" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><path d="m6 14 1.5-2.9A2 2 0 0 1 9.24 10H20a2 2 0 0 1 1.94 2.5l-1.54 6a2 2 0 0 1-1.95 1.5H4a2 2 0 0 1-2-2V5a2 2 0 0 1 2-2h3.9a2 2 0 0 1 1.69.9l.81 1.2a2 2 0 0 0 1.67.9H18a2 2 0 0 1 2 2v2"/></svg>
--- a/icons/hand.svg
+++ b/icons/hand.svg
@ -0,0 +1,2 @@
+<!-- Lucide hand, ISC license -->
+<svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24" fill="none" stroke="#000" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><path d="M18 11V6a2 2 0 0 0-4 0M14 10V4a2 2 0 0 0-4 0v2M10 10.5V6a2 2 0 0 0-4 0v8M18 8a2 2 0 1 1 4 0v6a8 8 0 0 1-8 8h-2c-2.8 0-4.5-.86-5.99-2.34l-3.6-3.6a2 2 0 0 1 2.83-2.82L7 15"/></svg>
--- a/icons/maximize.svg
+++ b/icons/maximize.svg
@ -0,0 +1,2 @@
+<!-- Lucide maximize, ISC license -->
+<svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24" fill="none" stroke="#000" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><path d="M8 3H5a2 2 0 0 0-2 2v3M21 8V5a2 2 0 0 0-2-2h-3M3 16v3a2 2 0 0 0 2 2h3M16 21h3a2 2 0 0 0 2-2v-3"/></svg>
--- a/icons/mic.svg
+++ b/icons/mic.svg
@ -0,0 +1,2 @@
+<!-- Lucide mic, ISC license -->
+<svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24" fill="none" stroke="#000" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><path d="M12 2a3 3 0 0 0-3 3v7a3 3 0 0 0 6 0V5a3 3 0 0 0-3-3Z"/><path d="M19 10v2a7 7 0 0 1-14 0v-2M12 19v3"/></svg>
--- a/icons/minus.svg
+++ b/icons/minus.svg
@ -0,0 +1,2 @@
+<!-- Lucide minus, ISC license -->
+<svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24" fill="none" stroke="#000" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><path d="M5 12h14"/></svg>
--- a/icons/move.svg
+++ b/icons/move.svg
@ -0,0 +1,2 @@
+<!-- Lucide move, ISC license -->
+<svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24" fill="none" stroke="#000" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><path d="M12 2v20M15 19l-3 3-3-3M19 9l3 3-3 3M2 12h20M5 9l-3 3 3 3M9 5l3-3 3 3"/></svg>
--- a/icons/octagon-x.svg
+++ b/icons/octagon-x.svg
@ -0,0 +1,2 @@
+<!-- Lucide octagon-x, ISC license -->
+<svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24" fill="none" stroke="#000" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><path d="m15 9-6 6M2.586 16.726A2 2 0 0 1 2 15.312V8.688a2 2 0 0 1 .586-1.414l4.688-4.688A2 2 0 0 1 8.688 2h6.624a2 2 0 0 1 1.414.586l4.688 4.688A2 2 0 0 1 22 8.688v6.624a2 2 0 0 1-.586 1.414l-4.688 4.688a2 2 0 0 1-1.414.586H8.688a2 2 0 0 1-1.414-.586zM9 9l6 6"/></svg>
--- a/icons/play.svg
+++ b/icons/play.svg
@ -0,0 +1,2 @@
+<!-- Lucide play, ISC license -->
+<svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24" fill="none" stroke="#000" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><polygon points="6 3 20 12 6 21 6 3"/></svg>
--- a/icons/power-off.svg
+++ b/icons/power-off.svg
@ -0,0 +1,2 @@
+<!-- Lucide power-off, ISC license -->
+<svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24" fill="none" stroke="#000" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><path d="M18.36 6.64A9 9 0 0 1 20.77 15M6.16 6.16a9 9 0 1 0 12.68 12.68M12 2v4M2 2l20 20"/></svg>
--- a/icons/power.svg
+++ b/icons/power.svg
@ -0,0 +1,2 @@
+<!-- Lucide power, ISC license -->
+<svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24" fill="none" stroke="#000" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><path d="M12 2v10M18.4 6.6a9 9 0 1 1-12.77.04"/></svg>
--- a/icons/radio-tower.svg
+++ b/icons/radio-tower.svg
@ -0,0 +1,2 @@
+<!-- Lucide radio-tower, ISC license -->
+<svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24" fill="none" stroke="#000" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><path d="M4.9 16.1C1 12.2 1 5.8 4.9 1.9M7.8 4.7a6.14 6.14 0 0 0-.8 7.5"/><circle cx="12" cy="9" r="2"/><path d="M16.2 4.8c2 2 2.26 5.11.8 7.47M19.1 1.9a9.96 9.96 0 0 1 0 14.1M9.5 18h5M8 22l4-11 4 11"/></svg>
--- a/icons/rotate-ccw.svg
+++ b/icons/rotate-ccw.svg
@ -0,0 +1,2 @@
+<!-- Lucide rotate-ccw, ISC license -->
+<svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24" fill="none" stroke="#000" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><path d="M3 12a9 9 0 1 0 9-9 9.75 9.75 0 0 0-6.74 2.74L3 8M3 3v5h5"/></svg>
--- a/icons/scan-face.svg
+++ b/icons/scan-face.svg
@ -0,0 +1,2 @@
+<!-- Lucide scan-face, ISC license -->
+<svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24" fill="none" stroke="#000" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><path d="M3 7V5a2 2 0 0 1 2-2h2M17 3h2a2 2 0 0 1 2 2v2M21 17v2a2 2 0 0 1-2 2h-2M7 21H5a2 2 0 0 1-2-2v-2M8 14s1.5 2 4 2 4-2 4-2M9 9h.01M15 9h.01"/></svg>
--- a/icons/scroll-text.svg
+++ b/icons/scroll-text.svg
@ -0,0 +1,2 @@
+<!-- Lucide scroll-text, ISC license -->
+<svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24" fill="none" stroke="#000" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><path d="M15 12h-5M15 8h-5M19 17V5a2 2 0 0 0-2-2H4M8 21h12a2 2 0 0 0 2-2v-1a1 1 0 0 0-1-1H11a1 1 0 0 0-1 1v1a2 2 0 1 1-4 0V5a2 2 0 1 0-4 0v2a1 1 0 0 0 1 1h3"/></svg>
--- a/icons/send.svg
+++ b/icons/send.svg
@ -0,0 +1,2 @@
+<!-- Lucide send, ISC license -->
+<svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24" fill="none" stroke="#000" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><path d="M14.536 21.686a.5.5 0 0 0 .937-.024l6.5-19a.496.496 0 0 0-.635-.635l-19 6.5a.5.5 0 0 0-.024.937l7.93 3.18a2 2 0 0 1 1.112 1.11zM21.854 2.147l-10.94 10.939"/></svg>
--- a/icons/shield-check.svg
+++ b/icons/shield-check.svg
@ -0,0 +1,2 @@
+<!-- Lucide shield-check, ISC license -->
+<svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24" fill="none" stroke="#000" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><path d="M20 13c0 5-3.5 7.5-7.66 8.95a1 1 0 0 1-.67-.01C7.5 20.5 4 18 4 13V6a1 1 0 0 1 1-1c2 0 4.5-1.2 6.24-2.72a1.17 1.17 0 0 1 1.52 0C14.51 3.81 17 5 19 5a1 1 0 0 1 1 1zM9 12l2 2 4-4"/></svg>
--- a/icons/square.svg
+++ b/icons/square.svg
@ -0,0 +1,2 @@
+<!-- Lucide square, ISC license -->
+<svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24" fill="none" stroke="#000" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><rect width="18" height="18" x="3" y="3" rx="2"/></svg>
--- a/icons/toggle-off.svg
+++ b/icons/toggle-off.svg
@ -0,0 +1,4 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="44" height="24" viewBox="0 0 44 24">
+  <rect x="0" y="0" width="44" height="24" rx="12" fill="#cbd3dc"/>
+  <circle cx="12" cy="12" r="9" fill="#ffffff"/>
+</svg>
--- a/icons/toggle-on.svg
+++ b/icons/toggle-on.svg
@ -0,0 +1,4 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="44" height="24" viewBox="0 0 44 24">
+  <rect x="0" y="0" width="44" height="24" rx="12" fill="#2878f0"/>
+  <circle cx="32" cy="12" r="9" fill="#ffffff"/>
+</svg>
--- a/icons/undo-2.svg
+++ b/icons/undo-2.svg
@ -0,0 +1,2 @@
+<!-- Lucide undo-2, ISC license -->
+<svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24" fill="none" stroke="#000" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><path d="M9 14 4 9l5-5M4 9h10.5a5.5 5.5 0 0 1 0 11H11"/></svg>
--- a/icons/volume-2.svg
+++ b/icons/volume-2.svg
@ -0,0 +1,2 @@
+<!-- Lucide volume-2, ISC license -->
+<svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24" fill="none" stroke="#000" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><path d="M11 4.702a.705.705 0 0 0-1.203-.498L6.413 7.587A1.4 1.4 0 0 1 5.416 8H3a1 1 0 0 0-1 1v6a1 1 0 0 0 1 1h2.416a1.4 1.4 0 0 1 .997.413l3.383 3.384A.705.705 0 0 0 11 19.298z"/><path d="M16 9a5 5 0 0 1 0 6M19.364 18.364a9 9 0 0 0 0-12.728"/></svg>
--- a/icons/x.svg
+++ b/icons/x.svg
@ -0,0 +1,2 @@
+<!-- Lucide x, ISC license -->
+<svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24" fill="none" stroke="#000" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"><path d="M18 6 6 18M6 6l12 12"/></svg>
--- a/include/absl/algorithm/algorithm.h
+++ b/include/absl/algorithm/algorithm.h
@ -0,0 +1,159 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// -----------------------------------------------------------------------------
+// File: algorithm.h
+// -----------------------------------------------------------------------------
+//
+// This header file contains Google extensions to the standard <algorithm> C++
+// header.
+
+#ifndef ABSL_ALGORITHM_ALGORITHM_H_
+#define ABSL_ALGORITHM_ALGORITHM_H_
+
+#include <algorithm>
+#include <iterator>
+#include <type_traits>
+
+#include "absl/base/config.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+
+namespace algorithm_internal {
+
+// Performs comparisons with operator==, similar to C++14's `std::equal_to<>`.
+struct EqualTo {
+  template <typename T, typename U>
+  bool operator()(const T& a, const U& b) const {
+    return a == b;
+  }
+};
+
+template <typename InputIter1, typename InputIter2, typename Pred>
+bool EqualImpl(InputIter1 first1, InputIter1 last1, InputIter2 first2,
+               InputIter2 last2, Pred pred, std::input_iterator_tag,
+               std::input_iterator_tag) {
+  while (true) {
+    if (first1 == last1) return first2 == last2;
+    if (first2 == last2) return false;
+    if (!pred(*first1, *first2)) return false;
+    ++first1;
+    ++first2;
+  }
+}
+
+template <typename InputIter1, typename InputIter2, typename Pred>
+bool EqualImpl(InputIter1 first1, InputIter1 last1, InputIter2 first2,
+               InputIter2 last2, Pred&& pred, std::random_access_iterator_tag,
+               std::random_access_iterator_tag) {
+  return (last1 - first1 == last2 - first2) &&
+         std::equal(first1, last1, first2, std::forward<Pred>(pred));
+}
+
+// When we are using our own internal predicate that just applies operator==, we
+// forward to the non-predicate form of std::equal. This enables an optimization
+// in libstdc++ that can result in std::memcmp being used for integer types.
+template <typename InputIter1, typename InputIter2>
+bool EqualImpl(InputIter1 first1, InputIter1 last1, InputIter2 first2,
+               InputIter2 last2, algorithm_internal::EqualTo /* unused */,
+               std::random_access_iterator_tag,
+               std::random_access_iterator_tag) {
+  return (last1 - first1 == last2 - first2) &&
+         std::equal(first1, last1, first2);
+}
+
+template <typename It>
+It RotateImpl(It first, It middle, It last, std::true_type) {
+  return std::rotate(first, middle, last);
+}
+
+template <typename It>
+It RotateImpl(It first, It middle, It last, std::false_type) {
+  std::rotate(first, middle, last);
+  return std::next(first, std::distance(middle, last));
+}
+
+}  // namespace algorithm_internal
+
+// equal()
+//
+// Compares the equality of two ranges specified by pairs of iterators, using
+// the given predicate, returning true iff for each corresponding iterator i1
+// and i2 in the first and second range respectively, pred(*i1, *i2) == true
+//
+// This comparison takes at most min(`last1` - `first1`, `last2` - `first2`)
+// invocations of the predicate. Additionally, if InputIter1 and InputIter2 are
+// both random-access iterators, and `last1` - `first1` != `last2` - `first2`,
+// then the predicate is never invoked and the function returns false.
+//
+// This is a C++11-compatible implementation of C++14 `std::equal`.  See
+// https://en.cppreference.com/w/cpp/algorithm/equal for more information.
+template <typename InputIter1, typename InputIter2, typename Pred>
+bool equal(InputIter1 first1, InputIter1 last1, InputIter2 first2,
+           InputIter2 last2, Pred&& pred) {
+  return algorithm_internal::EqualImpl(
+      first1, last1, first2, last2, std::forward<Pred>(pred),
+      typename std::iterator_traits<InputIter1>::iterator_category{},
+      typename std::iterator_traits<InputIter2>::iterator_category{});
+}
+
+// Overload of equal() that performs comparison of two ranges specified by pairs
+// of iterators using operator==.
+template <typename InputIter1, typename InputIter2>
+bool equal(InputIter1 first1, InputIter1 last1, InputIter2 first2,
+           InputIter2 last2) {
+  return absl::equal(first1, last1, first2, last2,
+                     algorithm_internal::EqualTo{});
+}
+
+// linear_search()
+//
+// Performs a linear search for `value` using the iterator `first` up to
+// but not including `last`, returning true if [`first`, `last`) contains an
+// element equal to `value`.
+//
+// A linear search is of O(n) complexity which is guaranteed to make at most
+// n = (`last` - `first`) comparisons. A linear search over short containers
+// may be faster than a binary search, even when the container is sorted.
+template <typename InputIterator, typename EqualityComparable>
+bool linear_search(InputIterator first, InputIterator last,
+                   const EqualityComparable& value) {
+  return std::find(first, last, value) != last;
+}
+
+// rotate()
+//
+// Performs a left rotation on a range of elements (`first`, `last`) such that
+// `middle` is now the first element. `rotate()` returns an iterator pointing to
+// the first element before rotation. This function is exactly the same as
+// `std::rotate`, but fixes a bug in gcc
+// <= 4.9 where `std::rotate` returns `void` instead of an iterator.
+//
+// The complexity of this algorithm is the same as that of `std::rotate`, but if
+// `ForwardIterator` is not a random-access iterator, then `absl::rotate`
+// performs an additional pass over the range to construct the return value.
+template <typename ForwardIterator>
+ForwardIterator rotate(ForwardIterator first, ForwardIterator middle,
+                       ForwardIterator last) {
+  return algorithm_internal::RotateImpl(
+      first, middle, last,
+      std::is_same<decltype(std::rotate(first, middle, last)),
+                   ForwardIterator>());
+}
+
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_ALGORITHM_ALGORITHM_H_
--- a/include/absl/algorithm/container.h
+++ b/include/absl/algorithm/container.h
--- a/include/absl/base/attributes.h
+++ b/include/absl/base/attributes.h
@ -0,0 +1,762 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// This header file defines macros for declaring attributes for functions,
+// types, and variables.
+//
+// These macros are used within Abseil and allow the compiler to optimize, where
+// applicable, certain function calls.
+//
+// Most macros here are exposing GCC or Clang features, and are stubbed out for
+// other compilers.
+//
+// GCC attributes documentation:
+//   https://gcc.gnu.org/onlinedocs/gcc-4.7.0/gcc/Function-Attributes.html
+//   https://gcc.gnu.org/onlinedocs/gcc-4.7.0/gcc/Variable-Attributes.html
+//   https://gcc.gnu.org/onlinedocs/gcc-4.7.0/gcc/Type-Attributes.html
+//
+// Most attributes in this file are already supported by GCC 4.7. However, some
+// of them are not supported in older version of Clang. Thus, we check
+// `__has_attribute()` first. If the check fails, we check if we are on GCC and
+// assume the attribute exists on GCC (which is verified on GCC 4.7).
+
+#ifndef ABSL_BASE_ATTRIBUTES_H_
+#define ABSL_BASE_ATTRIBUTES_H_
+
+#include "absl/base/config.h"
+
+// ABSL_HAVE_ATTRIBUTE
+//
+// A function-like feature checking macro that is a wrapper around
+// `__has_attribute`, which is defined by GCC 5+ and Clang and evaluates to a
+// nonzero constant integer if the attribute is supported or 0 if not.
+//
+// It evaluates to zero if `__has_attribute` is not defined by the compiler.
+//
+// GCC: https://gcc.gnu.org/gcc-5/changes.html
+// Clang: https://clang.llvm.org/docs/LanguageExtensions.html
+#ifdef __has_attribute
+#define ABSL_HAVE_ATTRIBUTE(x) __has_attribute(x)
+#else
+#define ABSL_HAVE_ATTRIBUTE(x) 0
+#endif
+
+// ABSL_HAVE_CPP_ATTRIBUTE
+//
+// A function-like feature checking macro that accepts C++11 style attributes.
+// It's a wrapper around `__has_cpp_attribute`, defined by ISO C++ SD-6
+// (https://en.cppreference.com/w/cpp/experimental/feature_test). If we don't
+// find `__has_cpp_attribute`, will evaluate to 0.
+#if defined(__cplusplus) && defined(__has_cpp_attribute)
+// NOTE: requiring __cplusplus above should not be necessary, but
+// works around https://bugs.llvm.org/show_bug.cgi?id=23435.
+#define ABSL_HAVE_CPP_ATTRIBUTE(x) __has_cpp_attribute(x)
+#else
+#define ABSL_HAVE_CPP_ATTRIBUTE(x) 0
+#endif
+
+// -----------------------------------------------------------------------------
+// Function Attributes
+// -----------------------------------------------------------------------------
+//
+// GCC: https://gcc.gnu.org/onlinedocs/gcc/Function-Attributes.html
+// Clang: https://clang.llvm.org/docs/AttributeReference.html
+
+// ABSL_PRINTF_ATTRIBUTE
+// ABSL_SCANF_ATTRIBUTE
+//
+// Tells the compiler to perform `printf` format string checking if the
+// compiler supports it; see the 'format' attribute in
+// <https://gcc.gnu.org/onlinedocs/gcc-4.7.0/gcc/Function-Attributes.html>.
+//
+// Note: As the GCC manual states, "[s]ince non-static C++ methods
+// have an implicit 'this' argument, the arguments of such methods
+// should be counted from two, not one."
+#if ABSL_HAVE_ATTRIBUTE(format) || (defined(__GNUC__) && !defined(__clang__))
+#define ABSL_PRINTF_ATTRIBUTE(string_index, first_to_check) \
+  __attribute__((__format__(__printf__, string_index, first_to_check)))
+#define ABSL_SCANF_ATTRIBUTE(string_index, first_to_check) \
+  __attribute__((__format__(__scanf__, string_index, first_to_check)))
+#else
+#define ABSL_PRINTF_ATTRIBUTE(string_index, first_to_check)
+#define ABSL_SCANF_ATTRIBUTE(string_index, first_to_check)
+#endif
+
+// ABSL_ATTRIBUTE_ALWAYS_INLINE
+// ABSL_ATTRIBUTE_NOINLINE
+//
+// Forces functions to either inline or not inline. Introduced in gcc 3.1.
+#if ABSL_HAVE_ATTRIBUTE(always_inline) || \
+    (defined(__GNUC__) && !defined(__clang__))
+#define ABSL_ATTRIBUTE_ALWAYS_INLINE __attribute__((always_inline))
+#define ABSL_HAVE_ATTRIBUTE_ALWAYS_INLINE 1
+#else
+#define ABSL_ATTRIBUTE_ALWAYS_INLINE
+#endif
+
+#if ABSL_HAVE_ATTRIBUTE(noinline) || (defined(__GNUC__) && !defined(__clang__))
+#define ABSL_ATTRIBUTE_NOINLINE __attribute__((noinline))
+#define ABSL_HAVE_ATTRIBUTE_NOINLINE 1
+#else
+#define ABSL_ATTRIBUTE_NOINLINE
+#endif
+
+// ABSL_ATTRIBUTE_NO_TAIL_CALL
+//
+// Prevents the compiler from optimizing away stack frames for functions which
+// end in a call to another function.
+#if ABSL_HAVE_ATTRIBUTE(disable_tail_calls)
+#define ABSL_HAVE_ATTRIBUTE_NO_TAIL_CALL 1
+#define ABSL_ATTRIBUTE_NO_TAIL_CALL __attribute__((disable_tail_calls))
+#elif defined(__GNUC__) && !defined(__clang__) && !defined(__e2k__)
+#define ABSL_HAVE_ATTRIBUTE_NO_TAIL_CALL 1
+#define ABSL_ATTRIBUTE_NO_TAIL_CALL \
+  __attribute__((optimize("no-optimize-sibling-calls")))
+#else
+#define ABSL_ATTRIBUTE_NO_TAIL_CALL
+#define ABSL_HAVE_ATTRIBUTE_NO_TAIL_CALL 0
+#endif
+
+// ABSL_ATTRIBUTE_WEAK
+//
+// Tags a function as weak for the purposes of compilation and linking.
+// Weak attributes did not work properly in LLVM's Windows backend before
+// 9.0.0, so disable them there. See https://bugs.llvm.org/show_bug.cgi?id=37598
+// for further information.
+// The MinGW compiler doesn't complain about the weak attribute until the link
+// step, presumably because Windows doesn't use ELF binaries.
+#if (ABSL_HAVE_ATTRIBUTE(weak) ||                                         \
+     (defined(__GNUC__) && !defined(__clang__))) &&                       \
+    (!defined(_WIN32) || (defined(__clang__) && __clang_major__ >= 9)) && \
+    !defined(__MINGW32__)
+#undef ABSL_ATTRIBUTE_WEAK
+#define ABSL_ATTRIBUTE_WEAK __attribute__((weak))
+#define ABSL_HAVE_ATTRIBUTE_WEAK 1
+#else
+#define ABSL_ATTRIBUTE_WEAK
+#define ABSL_HAVE_ATTRIBUTE_WEAK 0
+#endif
+
+// ABSL_ATTRIBUTE_NONNULL
+//
+// Tells the compiler either (a) that a particular function parameter
+// should be a non-null pointer, or (b) that all pointer arguments should
+// be non-null.
+//
+// Note: As the GCC manual states, "[s]ince non-static C++ methods
+// have an implicit 'this' argument, the arguments of such methods
+// should be counted from two, not one."
+//
+// Args are indexed starting at 1.
+//
+// For non-static class member functions, the implicit `this` argument
+// is arg 1, and the first explicit argument is arg 2. For static class member
+// functions, there is no implicit `this`, and the first explicit argument is
+// arg 1.
+//
+// Example:
+//
+//   /* arg_a cannot be null, but arg_b can */
+//   void Function(void* arg_a, void* arg_b) ABSL_ATTRIBUTE_NONNULL(1);
+//
+//   class C {
+//     /* arg_a cannot be null, but arg_b can */
+//     void Method(void* arg_a, void* arg_b) ABSL_ATTRIBUTE_NONNULL(2);
+//
+//     /* arg_a cannot be null, but arg_b can */
+//     static void StaticMethod(void* arg_a, void* arg_b)
+//     ABSL_ATTRIBUTE_NONNULL(1);
+//   };
+//
+// If no arguments are provided, then all pointer arguments should be non-null.
+//
+//  /* No pointer arguments may be null. */
+//  void Function(void* arg_a, void* arg_b, int arg_c) ABSL_ATTRIBUTE_NONNULL();
+//
+// NOTE: The GCC nonnull attribute actually accepts a list of arguments, but
+// ABSL_ATTRIBUTE_NONNULL does not.
+#if ABSL_HAVE_ATTRIBUTE(nonnull) || (defined(__GNUC__) && !defined(__clang__))
+#define ABSL_ATTRIBUTE_NONNULL(arg_index) __attribute__((nonnull(arg_index)))
+#else
+#define ABSL_ATTRIBUTE_NONNULL(...)
+#endif
+
+// ABSL_ATTRIBUTE_NORETURN
+//
+// Tells the compiler that a given function never returns.
+#if ABSL_HAVE_ATTRIBUTE(noreturn) || (defined(__GNUC__) && !defined(__clang__))
+#define ABSL_ATTRIBUTE_NORETURN __attribute__((noreturn))
+#elif defined(_MSC_VER)
+#define ABSL_ATTRIBUTE_NORETURN __declspec(noreturn)
+#else
+#define ABSL_ATTRIBUTE_NORETURN
+#endif
+
+// ABSL_ATTRIBUTE_NO_SANITIZE_ADDRESS
+//
+// Tells the AddressSanitizer (or other memory testing tools) to ignore a given
+// function. Useful for cases when a function reads random locations on stack,
+// calls _exit from a cloned subprocess, deliberately accesses buffer
+// out of bounds or does other scary things with memory.
+// NOTE: GCC supports AddressSanitizer(asan) since 4.8.
+// https://gcc.gnu.org/gcc-4.8/changes.html
+#if ABSL_HAVE_ATTRIBUTE(no_sanitize_address)
+#define ABSL_ATTRIBUTE_NO_SANITIZE_ADDRESS __attribute__((no_sanitize_address))
+#elif defined(_MSC_VER) && _MSC_VER >= 1928
+// https://docs.microsoft.com/en-us/cpp/cpp/no-sanitize-address
+#define ABSL_ATTRIBUTE_NO_SANITIZE_ADDRESS __declspec(no_sanitize_address)
+#else
+#define ABSL_ATTRIBUTE_NO_SANITIZE_ADDRESS
+#endif
+
+// ABSL_ATTRIBUTE_NO_SANITIZE_MEMORY
+//
+// Tells the MemorySanitizer to relax the handling of a given function. All "Use
+// of uninitialized value" warnings from such functions will be suppressed, and
+// all values loaded from memory will be considered fully initialized.  This
+// attribute is similar to the ABSL_ATTRIBUTE_NO_SANITIZE_ADDRESS attribute
+// above, but deals with initialized-ness rather than addressability issues.
+// NOTE: MemorySanitizer(msan) is supported by Clang but not GCC.
+#if ABSL_HAVE_ATTRIBUTE(no_sanitize_memory)
+#define ABSL_ATTRIBUTE_NO_SANITIZE_MEMORY __attribute__((no_sanitize_memory))
+#else
+#define ABSL_ATTRIBUTE_NO_SANITIZE_MEMORY
+#endif
+
+// ABSL_ATTRIBUTE_NO_SANITIZE_THREAD
+//
+// Tells the ThreadSanitizer to not instrument a given function.
+// NOTE: GCC supports ThreadSanitizer(tsan) since 4.8.
+// https://gcc.gnu.org/gcc-4.8/changes.html
+#if ABSL_HAVE_ATTRIBUTE(no_sanitize_thread)
+#define ABSL_ATTRIBUTE_NO_SANITIZE_THREAD __attribute__((no_sanitize_thread))
+#else
+#define ABSL_ATTRIBUTE_NO_SANITIZE_THREAD
+#endif
+
+// ABSL_ATTRIBUTE_NO_SANITIZE_UNDEFINED
+//
+// Tells the UndefinedSanitizer to ignore a given function. Useful for cases
+// where certain behavior (eg. division by zero) is being used intentionally.
+// NOTE: GCC supports UndefinedBehaviorSanitizer(ubsan) since 4.9.
+// https://gcc.gnu.org/gcc-4.9/changes.html
+#if ABSL_HAVE_ATTRIBUTE(no_sanitize_undefined)
+#define ABSL_ATTRIBUTE_NO_SANITIZE_UNDEFINED \
+  __attribute__((no_sanitize_undefined))
+#elif ABSL_HAVE_ATTRIBUTE(no_sanitize)
+#define ABSL_ATTRIBUTE_NO_SANITIZE_UNDEFINED \
+  __attribute__((no_sanitize("undefined")))
+#else
+#define ABSL_ATTRIBUTE_NO_SANITIZE_UNDEFINED
+#endif
+
+// ABSL_ATTRIBUTE_NO_SANITIZE_CFI
+//
+// Tells the ControlFlowIntegrity sanitizer to not instrument a given function.
+// See https://clang.llvm.org/docs/ControlFlowIntegrity.html for details.
+#if ABSL_HAVE_ATTRIBUTE(no_sanitize)
+#define ABSL_ATTRIBUTE_NO_SANITIZE_CFI __attribute__((no_sanitize("cfi")))
+#else
+#define ABSL_ATTRIBUTE_NO_SANITIZE_CFI
+#endif
+
+// ABSL_ATTRIBUTE_NO_SANITIZE_SAFESTACK
+//
+// Tells the SafeStack to not instrument a given function.
+// See https://clang.llvm.org/docs/SafeStack.html for details.
+#if ABSL_HAVE_ATTRIBUTE(no_sanitize)
+#define ABSL_ATTRIBUTE_NO_SANITIZE_SAFESTACK \
+  __attribute__((no_sanitize("safe-stack")))
+#else
+#define ABSL_ATTRIBUTE_NO_SANITIZE_SAFESTACK
+#endif
+
+// ABSL_ATTRIBUTE_RETURNS_NONNULL
+//
+// Tells the compiler that a particular function never returns a null pointer.
+#if ABSL_HAVE_ATTRIBUTE(returns_nonnull)
+#define ABSL_ATTRIBUTE_RETURNS_NONNULL __attribute__((returns_nonnull))
+#else
+#define ABSL_ATTRIBUTE_RETURNS_NONNULL
+#endif
+
+// ABSL_HAVE_ATTRIBUTE_SECTION
+//
+// Indicates whether labeled sections are supported. Weak symbol support is
+// a prerequisite. Labeled sections are not supported on Darwin/iOS.
+#ifdef ABSL_HAVE_ATTRIBUTE_SECTION
+#error ABSL_HAVE_ATTRIBUTE_SECTION cannot be directly set
+#elif (ABSL_HAVE_ATTRIBUTE(section) ||                \
+       (defined(__GNUC__) && !defined(__clang__))) && \
+    !defined(__APPLE__) && ABSL_HAVE_ATTRIBUTE_WEAK
+#define ABSL_HAVE_ATTRIBUTE_SECTION 1
+
+// ABSL_ATTRIBUTE_SECTION
+//
+// Tells the compiler/linker to put a given function into a section and define
+// `__start_ ## name` and `__stop_ ## name` symbols to bracket the section.
+// This functionality is supported by GNU linker.  Any function annotated with
+// `ABSL_ATTRIBUTE_SECTION` must not be inlined, or it will be placed into
+// whatever section its caller is placed into.
+//
+#ifndef ABSL_ATTRIBUTE_SECTION
+#define ABSL_ATTRIBUTE_SECTION(name) \
+  __attribute__((section(#name))) __attribute__((noinline))
+#endif
+
+// ABSL_ATTRIBUTE_SECTION_VARIABLE
+//
+// Tells the compiler/linker to put a given variable into a section and define
+// `__start_ ## name` and `__stop_ ## name` symbols to bracket the section.
+// This functionality is supported by GNU linker.
+#ifndef ABSL_ATTRIBUTE_SECTION_VARIABLE
+#ifdef _AIX
+// __attribute__((section(#name))) on AIX is achived by using the `.csect` psudo
+// op which includes an additional integer as part of its syntax indcating
+// alignment. If data fall under different alignments then you might get a
+// compilation error indicating a `Section type conflict`.
+#define ABSL_ATTRIBUTE_SECTION_VARIABLE(name)
+#else
+#define ABSL_ATTRIBUTE_SECTION_VARIABLE(name) __attribute__((section(#name)))
+#endif
+#endif
+
+// ABSL_DECLARE_ATTRIBUTE_SECTION_VARS
+//
+// A weak section declaration to be used as a global declaration
+// for ABSL_ATTRIBUTE_SECTION_START|STOP(name) to compile and link
+// even without functions with ABSL_ATTRIBUTE_SECTION(name).
+// ABSL_DEFINE_ATTRIBUTE_SECTION should be in the exactly one file; it's
+// a no-op on ELF but not on Mach-O.
+//
+#ifndef ABSL_DECLARE_ATTRIBUTE_SECTION_VARS
+#define ABSL_DECLARE_ATTRIBUTE_SECTION_VARS(name)   \
+  extern char __start_##name[] ABSL_ATTRIBUTE_WEAK; \
+  extern char __stop_##name[] ABSL_ATTRIBUTE_WEAK
+#endif
+#ifndef ABSL_DEFINE_ATTRIBUTE_SECTION_VARS
+#define ABSL_INIT_ATTRIBUTE_SECTION_VARS(name)
+#define ABSL_DEFINE_ATTRIBUTE_SECTION_VARS(name)
+#endif
+
+// ABSL_ATTRIBUTE_SECTION_START
+//
+// Returns `void*` pointers to start/end of a section of code with
+// functions having ABSL_ATTRIBUTE_SECTION(name).
+// Returns 0 if no such functions exist.
+// One must ABSL_DECLARE_ATTRIBUTE_SECTION_VARS(name) for this to compile and
+// link.
+//
+#define ABSL_ATTRIBUTE_SECTION_START(name) \
+  (reinterpret_cast<void *>(__start_##name))
+#define ABSL_ATTRIBUTE_SECTION_STOP(name) \
+  (reinterpret_cast<void *>(__stop_##name))
+
+#else  // !ABSL_HAVE_ATTRIBUTE_SECTION
+
+#define ABSL_HAVE_ATTRIBUTE_SECTION 0
+
+// provide dummy definitions
+#define ABSL_ATTRIBUTE_SECTION(name)
+#define ABSL_ATTRIBUTE_SECTION_VARIABLE(name)
+#define ABSL_INIT_ATTRIBUTE_SECTION_VARS(name)
+#define ABSL_DEFINE_ATTRIBUTE_SECTION_VARS(name)
+#define ABSL_DECLARE_ATTRIBUTE_SECTION_VARS(name)
+#define ABSL_ATTRIBUTE_SECTION_START(name) (reinterpret_cast<void *>(0))
+#define ABSL_ATTRIBUTE_SECTION_STOP(name) (reinterpret_cast<void *>(0))
+
+#endif  // ABSL_ATTRIBUTE_SECTION
+
+// ABSL_ATTRIBUTE_STACK_ALIGN_FOR_OLD_LIBC
+//
+// Support for aligning the stack on 32-bit x86.
+#if ABSL_HAVE_ATTRIBUTE(force_align_arg_pointer) || \
+    (defined(__GNUC__) && !defined(__clang__))
+#if defined(__i386__)
+#define ABSL_ATTRIBUTE_STACK_ALIGN_FOR_OLD_LIBC \
+  __attribute__((force_align_arg_pointer))
+#define ABSL_REQUIRE_STACK_ALIGN_TRAMPOLINE (0)
+#elif defined(__x86_64__)
+#define ABSL_REQUIRE_STACK_ALIGN_TRAMPOLINE (1)
+#define ABSL_ATTRIBUTE_STACK_ALIGN_FOR_OLD_LIBC
+#else  // !__i386__ && !__x86_64
+#define ABSL_REQUIRE_STACK_ALIGN_TRAMPOLINE (0)
+#define ABSL_ATTRIBUTE_STACK_ALIGN_FOR_OLD_LIBC
+#endif  // __i386__
+#else
+#define ABSL_ATTRIBUTE_STACK_ALIGN_FOR_OLD_LIBC
+#define ABSL_REQUIRE_STACK_ALIGN_TRAMPOLINE (0)
+#endif
+
+// ABSL_MUST_USE_RESULT
+//
+// Tells the compiler to warn about unused results.
+//
+// For code or headers that are assured to only build with C++17 and up, prefer
+// just using the standard `[[nodiscard]]` directly over this macro.
+//
+// When annotating a function, it must appear as the first part of the
+// declaration or definition. The compiler will warn if the return value from
+// such a function is unused:
+//
+//   ABSL_MUST_USE_RESULT Sprocket* AllocateSprocket();
+//   AllocateSprocket();  // Triggers a warning.
+//
+// When annotating a class, it is equivalent to annotating every function which
+// returns an instance.
+//
+//   class ABSL_MUST_USE_RESULT Sprocket {};
+//   Sprocket();  // Triggers a warning.
+//
+//   Sprocket MakeSprocket();
+//   MakeSprocket();  // Triggers a warning.
+//
+// Note that references and pointers are not instances:
+//
+//   Sprocket* SprocketPointer();
+//   SprocketPointer();  // Does *not* trigger a warning.
+//
+// ABSL_MUST_USE_RESULT allows using cast-to-void to suppress the unused result
+// warning. For that, warn_unused_result is used only for clang but not for gcc.
+// https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66425
+//
+// Note: past advice was to place the macro after the argument list.
+//
+// TODO(b/176172494): Use ABSL_HAVE_CPP_ATTRIBUTE(nodiscard) when all code is
+// compliant with the stricter [[nodiscard]].
+#if defined(__clang__) && ABSL_HAVE_ATTRIBUTE(warn_unused_result)
+#define ABSL_MUST_USE_RESULT __attribute__((warn_unused_result))
+#else
+#define ABSL_MUST_USE_RESULT
+#endif
+
+// ABSL_ATTRIBUTE_HOT, ABSL_ATTRIBUTE_COLD
+//
+// Tells GCC that a function is hot or cold. GCC can use this information to
+// improve static analysis, i.e. a conditional branch to a cold function
+// is likely to be not-taken.
+// This annotation is used for function declarations.
+//
+// Example:
+//
+//   int foo() ABSL_ATTRIBUTE_HOT;
+#if ABSL_HAVE_ATTRIBUTE(hot) || (defined(__GNUC__) && !defined(__clang__))
+#define ABSL_ATTRIBUTE_HOT __attribute__((hot))
+#else
+#define ABSL_ATTRIBUTE_HOT
+#endif
+
+#if ABSL_HAVE_ATTRIBUTE(cold) || (defined(__GNUC__) && !defined(__clang__))
+#define ABSL_ATTRIBUTE_COLD __attribute__((cold))
+#else
+#define ABSL_ATTRIBUTE_COLD
+#endif
+
+// ABSL_XRAY_ALWAYS_INSTRUMENT, ABSL_XRAY_NEVER_INSTRUMENT, ABSL_XRAY_LOG_ARGS
+//
+// We define the ABSL_XRAY_ALWAYS_INSTRUMENT and ABSL_XRAY_NEVER_INSTRUMENT
+// macro used as an attribute to mark functions that must always or never be
+// instrumented by XRay. Currently, this is only supported in Clang/LLVM.
+//
+// For reference on the LLVM XRay instrumentation, see
+// http://llvm.org/docs/XRay.html.
+//
+// A function with the XRAY_ALWAYS_INSTRUMENT macro attribute in its declaration
+// will always get the XRay instrumentation sleds. These sleds may introduce
+// some binary size and runtime overhead and must be used sparingly.
+//
+// These attributes only take effect when the following conditions are met:
+//
+//   * The file/target is built in at least C++11 mode, with a Clang compiler
+//     that supports XRay attributes.
+//   * The file/target is built with the -fxray-instrument flag set for the
+//     Clang/LLVM compiler.
+//   * The function is defined in the translation unit (the compiler honors the
+//     attribute in either the definition or the declaration, and must match).
+//
+// There are cases when, even when building with XRay instrumentation, users
+// might want to control specifically which functions are instrumented for a
+// particular build using special-case lists provided to the compiler. These
+// special case lists are provided to Clang via the
+// -fxray-always-instrument=... and -fxray-never-instrument=... flags. The
+// attributes in source take precedence over these special-case lists.
+//
+// To disable the XRay attributes at build-time, users may define
+// ABSL_NO_XRAY_ATTRIBUTES. Do NOT define ABSL_NO_XRAY_ATTRIBUTES on specific
+// packages/targets, as this may lead to conflicting definitions of functions at
+// link-time.
+//
+// XRay isn't currently supported on Android:
+// https://github.com/android/ndk/issues/368
+#if ABSL_HAVE_CPP_ATTRIBUTE(clang::xray_always_instrument) && \
+    !defined(ABSL_NO_XRAY_ATTRIBUTES) && !defined(__ANDROID__)
+#define ABSL_XRAY_ALWAYS_INSTRUMENT [[clang::xray_always_instrument]]
+#define ABSL_XRAY_NEVER_INSTRUMENT [[clang::xray_never_instrument]]
+#if ABSL_HAVE_CPP_ATTRIBUTE(clang::xray_log_args)
+#define ABSL_XRAY_LOG_ARGS(N) \
+  [[clang::xray_always_instrument, clang::xray_log_args(N)]]
+#else
+#define ABSL_XRAY_LOG_ARGS(N) [[clang::xray_always_instrument]]
+#endif
+#else
+#define ABSL_XRAY_ALWAYS_INSTRUMENT
+#define ABSL_XRAY_NEVER_INSTRUMENT
+#define ABSL_XRAY_LOG_ARGS(N)
+#endif
+
+// ABSL_ATTRIBUTE_REINITIALIZES
+//
+// Indicates that a member function reinitializes the entire object to a known
+// state, independent of the previous state of the object.
+//
+// The clang-tidy check bugprone-use-after-move allows member functions marked
+// with this attribute to be called on objects that have been moved from;
+// without the attribute, this would result in a use-after-move warning.
+#if ABSL_HAVE_CPP_ATTRIBUTE(clang::reinitializes)
+#define ABSL_ATTRIBUTE_REINITIALIZES [[clang::reinitializes]]
+#else
+#define ABSL_ATTRIBUTE_REINITIALIZES
+#endif
+
+// -----------------------------------------------------------------------------
+// Variable Attributes
+// -----------------------------------------------------------------------------
+
+// ABSL_ATTRIBUTE_UNUSED
+//
+// Prevents the compiler from complaining about variables that appear unused.
+//
+// For code or headers that are assured to only build with C++17 and up, prefer
+// just using the standard '[[maybe_unused]]' directly over this macro.
+//
+// Due to differences in positioning requirements between the old, compiler
+// specific __attribute__ syntax and the now standard [[maybe_unused]], this
+// macro does not attempt to take advantage of '[[maybe_unused]]'.
+#if ABSL_HAVE_ATTRIBUTE(unused) || (defined(__GNUC__) && !defined(__clang__))
+#undef ABSL_ATTRIBUTE_UNUSED
+#define ABSL_ATTRIBUTE_UNUSED __attribute__((__unused__))
+#else
+#define ABSL_ATTRIBUTE_UNUSED
+#endif
+
+// ABSL_ATTRIBUTE_INITIAL_EXEC
+//
+// Tells the compiler to use "initial-exec" mode for a thread-local variable.
+// See http://people.redhat.com/drepper/tls.pdf for the gory details.
+#if ABSL_HAVE_ATTRIBUTE(tls_model) || (defined(__GNUC__) && !defined(__clang__))
+#define ABSL_ATTRIBUTE_INITIAL_EXEC __attribute__((tls_model("initial-exec")))
+#else
+#define ABSL_ATTRIBUTE_INITIAL_EXEC
+#endif
+
+// ABSL_ATTRIBUTE_PACKED
+//
+// Instructs the compiler not to use natural alignment for a tagged data
+// structure, but instead to reduce its alignment to 1.
+//
+// Therefore, DO NOT APPLY THIS ATTRIBUTE TO STRUCTS CONTAINING ATOMICS. Doing
+// so can cause atomic variables to be mis-aligned and silently violate
+// atomicity on x86.
+//
+// This attribute can either be applied to members of a structure or to a
+// structure in its entirety. Applying this attribute (judiciously) to a
+// structure in its entirety to optimize the memory footprint of very
+// commonly-used structs is fine. Do not apply this attribute to a structure in
+// its entirety if the purpose is to control the offsets of the members in the
+// structure. Instead, apply this attribute only to structure members that need
+// it.
+//
+// When applying ABSL_ATTRIBUTE_PACKED only to specific structure members the
+// natural alignment of structure members not annotated is preserved. Aligned
+// member accesses are faster than non-aligned member accesses even if the
+// targeted microprocessor supports non-aligned accesses.
+#if ABSL_HAVE_ATTRIBUTE(packed) || (defined(__GNUC__) && !defined(__clang__))
+#define ABSL_ATTRIBUTE_PACKED __attribute__((__packed__))
+#else
+#define ABSL_ATTRIBUTE_PACKED
+#endif
+
+// ABSL_ATTRIBUTE_FUNC_ALIGN
+//
+// Tells the compiler to align the function start at least to certain
+// alignment boundary
+#if ABSL_HAVE_ATTRIBUTE(aligned) || (defined(__GNUC__) && !defined(__clang__))
+#define ABSL_ATTRIBUTE_FUNC_ALIGN(bytes) __attribute__((aligned(bytes)))
+#else
+#define ABSL_ATTRIBUTE_FUNC_ALIGN(bytes)
+#endif
+
+// ABSL_FALLTHROUGH_INTENDED
+//
+// Annotates implicit fall-through between switch labels, allowing a case to
+// indicate intentional fallthrough and turn off warnings about any lack of a
+// `break` statement. The ABSL_FALLTHROUGH_INTENDED macro should be followed by
+// a semicolon and can be used in most places where `break` can, provided that
+// no statements exist between it and the next switch label.
+//
+// Example:
+//
+//  switch (x) {
+//    case 40:
+//    case 41:
+//      if (truth_is_out_there) {
+//        ++x;
+//        ABSL_FALLTHROUGH_INTENDED;  // Use instead of/along with annotations
+//                                    // in comments
+//      } else {
+//        return x;
+//      }
+//    case 42:
+//      ...
+//
+// Notes: When supported, GCC and Clang can issue a warning on switch labels
+// with unannotated fallthrough using the warning `-Wimplicit-fallthrough`. See
+// clang documentation on language extensions for details:
+// https://clang.llvm.org/docs/AttributeReference.html#fallthrough-clang-fallthrough
+//
+// When used with unsupported compilers, the ABSL_FALLTHROUGH_INTENDED macro has
+// no effect on diagnostics. In any case this macro has no effect on runtime
+// behavior and performance of code.
+
+#ifdef ABSL_FALLTHROUGH_INTENDED
+#error "ABSL_FALLTHROUGH_INTENDED should not be defined."
+#elif ABSL_HAVE_CPP_ATTRIBUTE(fallthrough)
+#define ABSL_FALLTHROUGH_INTENDED [[fallthrough]]
+#elif ABSL_HAVE_CPP_ATTRIBUTE(clang::fallthrough)
+#define ABSL_FALLTHROUGH_INTENDED [[clang::fallthrough]]
+#elif ABSL_HAVE_CPP_ATTRIBUTE(gnu::fallthrough)
+#define ABSL_FALLTHROUGH_INTENDED [[gnu::fallthrough]]
+#else
+#define ABSL_FALLTHROUGH_INTENDED \
+  do {                            \
+  } while (0)
+#endif
+
+// ABSL_DEPRECATED()
+//
+// Marks a deprecated class, struct, enum, function, method and variable
+// declarations. The macro argument is used as a custom diagnostic message (e.g.
+// suggestion of a better alternative).
+//
+// For code or headers that are assured to only build with C++14 and up, prefer
+// just using the standard `[[deprecated("message")]]` directly over this macro.
+//
+// Examples:
+//
+//   class ABSL_DEPRECATED("Use Bar instead") Foo {...};
+//
+//   ABSL_DEPRECATED("Use Baz() instead") void Bar() {...}
+//
+//   template <typename T>
+//   ABSL_DEPRECATED("Use DoThat() instead")
+//   void DoThis();
+//
+//   enum FooEnum {
+//     kBar ABSL_DEPRECATED("Use kBaz instead"),
+//   };
+//
+// Every usage of a deprecated entity will trigger a warning when compiled with
+// GCC/Clang's `-Wdeprecated-declarations` option. Google's production toolchain
+// turns this warning off by default, instead relying on clang-tidy to report
+// new uses of deprecated code.
+#if ABSL_HAVE_ATTRIBUTE(deprecated)
+#define ABSL_DEPRECATED(message) __attribute__((deprecated(message)))
+#else
+#define ABSL_DEPRECATED(message)
+#endif
+
+// ABSL_CONST_INIT
+//
+// A variable declaration annotated with the `ABSL_CONST_INIT` attribute will
+// not compile (on supported platforms) unless the variable has a constant
+// initializer. This is useful for variables with static and thread storage
+// duration, because it guarantees that they will not suffer from the so-called
+// "static init order fiasco".
+//
+// This attribute must be placed on the initializing declaration of the
+// variable. Some compilers will give a -Wmissing-constinit warning when this
+// attribute is placed on some other declaration but missing from the
+// initializing declaration.
+//
+// In some cases (notably with thread_local variables), `ABSL_CONST_INIT` can
+// also be used in a non-initializing declaration to tell the compiler that a
+// variable is already initialized, reducing overhead that would otherwise be
+// incurred by a hidden guard variable. Thus annotating all declarations with
+// this attribute is recommended to potentially enhance optimization.
+//
+// Example:
+//
+//   class MyClass {
+//    public:
+//     ABSL_CONST_INIT static MyType my_var;
+//   };
+//
+//   ABSL_CONST_INIT MyType MyClass::my_var = MakeMyType(...);
+//
+// For code or headers that are assured to only build with C++20 and up, prefer
+// just using the standard `constinit` keyword directly over this macro.
+//
+// Note that this attribute is redundant if the variable is declared constexpr.
+#if defined(__cpp_constinit) && __cpp_constinit >= 201907L
+#define ABSL_CONST_INIT constinit
+#elif ABSL_HAVE_CPP_ATTRIBUTE(clang::require_constant_initialization)
+#define ABSL_CONST_INIT [[clang::require_constant_initialization]]
+#else
+#define ABSL_CONST_INIT
+#endif
+
+// ABSL_ATTRIBUTE_PURE_FUNCTION
+//
+// ABSL_ATTRIBUTE_PURE_FUNCTION is used to annotate declarations of "pure"
+// functions. A function is pure if its return value is only a function of its
+// arguments. The pure attribute prohibits a function from modifying the state
+// of the program that is observable by means other than inspecting the
+// function's return value. Declaring such functions with the pure attribute
+// allows the compiler to avoid emitting some calls in repeated invocations of
+// the function with the same argument values.
+//
+// Example:
+//
+//  ABSL_ATTRIBUTE_PURE_FUNCTION int64_t ToInt64Milliseconds(Duration d);
+#if ABSL_HAVE_CPP_ATTRIBUTE(gnu::pure)
+#define ABSL_ATTRIBUTE_PURE_FUNCTION [[gnu::pure]]
+#elif ABSL_HAVE_ATTRIBUTE(pure)
+#define ABSL_ATTRIBUTE_PURE_FUNCTION __attribute__((pure))
+#else
+#define ABSL_ATTRIBUTE_PURE_FUNCTION
+#endif
+
+// ABSL_ATTRIBUTE_LIFETIME_BOUND indicates that a resource owned by a function
+// parameter or implicit object parameter is retained by the return value of the
+// annotated function (or, for a parameter of a constructor, in the value of the
+// constructed object). This attribute causes warnings to be produced if a
+// temporary object does not live long enough.
+//
+// When applied to a reference parameter, the referenced object is assumed to be
+// retained by the return value of the function. When applied to a non-reference
+// parameter (for example, a pointer or a class type), all temporaries
+// referenced by the parameter are assumed to be retained by the return value of
+// the function.
+//
+// See also the upstream documentation:
+// https://clang.llvm.org/docs/AttributeReference.html#lifetimebound
+#if ABSL_HAVE_CPP_ATTRIBUTE(clang::lifetimebound)
+#define ABSL_ATTRIBUTE_LIFETIME_BOUND [[clang::lifetimebound]]
+#elif ABSL_HAVE_ATTRIBUTE(lifetimebound)
+#define ABSL_ATTRIBUTE_LIFETIME_BOUND __attribute__((lifetimebound))
+#else
+#define ABSL_ATTRIBUTE_LIFETIME_BOUND
+#endif
+
+#endif  // ABSL_BASE_ATTRIBUTES_H_
--- a/include/absl/base/call_once.h
+++ b/include/absl/base/call_once.h
@ -0,0 +1,219 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// -----------------------------------------------------------------------------
+// File: call_once.h
+// -----------------------------------------------------------------------------
+//
+// This header file provides an Abseil version of `std::call_once` for invoking
+// a given function at most once, across all threads. This Abseil version is
+// faster than the C++11 version and incorporates the C++17 argument-passing
+// fix, so that (for example) non-const references may be passed to the invoked
+// function.
+
+#ifndef ABSL_BASE_CALL_ONCE_H_
+#define ABSL_BASE_CALL_ONCE_H_
+
+#include <algorithm>
+#include <atomic>
+#include <cstdint>
+#include <type_traits>
+#include <utility>
+
+#include "absl/base/internal/invoke.h"
+#include "absl/base/internal/low_level_scheduling.h"
+#include "absl/base/internal/raw_logging.h"
+#include "absl/base/internal/scheduling_mode.h"
+#include "absl/base/internal/spinlock_wait.h"
+#include "absl/base/macros.h"
+#include "absl/base/optimization.h"
+#include "absl/base/port.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+
+class once_flag;
+
+namespace base_internal {
+std::atomic<uint32_t>* ControlWord(absl::once_flag* flag);
+}  // namespace base_internal
+
+// call_once()
+//
+// For all invocations using a given `once_flag`, invokes a given `fn` exactly
+// once across all threads. The first call to `call_once()` with a particular
+// `once_flag` argument (that does not throw an exception) will run the
+// specified function with the provided `args`; other calls with the same
+// `once_flag` argument will not run the function, but will wait
+// for the provided function to finish running (if it is still running).
+//
+// This mechanism provides a safe, simple, and fast mechanism for one-time
+// initialization in a multi-threaded process.
+//
+// Example:
+//
+// class MyInitClass {
+//  public:
+//  ...
+//  mutable absl::once_flag once_;
+//
+//  MyInitClass* init() const {
+//    absl::call_once(once_, &MyInitClass::Init, this);
+//    return ptr_;
+//  }
+//
+template <typename Callable, typename... Args>
+void call_once(absl::once_flag& flag, Callable&& fn, Args&&... args);
+
+// once_flag
+//
+// Objects of this type are used to distinguish calls to `call_once()` and
+// ensure the provided function is only invoked once across all threads. This
+// type is not copyable or movable. However, it has a `constexpr`
+// constructor, and is safe to use as a namespace-scoped global variable.
+class once_flag {
+ public:
+  constexpr once_flag() : control_(0) {}
+  once_flag(const once_flag&) = delete;
+  once_flag& operator=(const once_flag&) = delete;
+
+ private:
+  friend std::atomic<uint32_t>* base_internal::ControlWord(once_flag* flag);
+  std::atomic<uint32_t> control_;
+};
+
+//------------------------------------------------------------------------------
+// End of public interfaces.
+// Implementation details follow.
+//------------------------------------------------------------------------------
+
+namespace base_internal {
+
+// Like call_once, but uses KERNEL_ONLY scheduling. Intended to be used to
+// initialize entities used by the scheduler implementation.
+template <typename Callable, typename... Args>
+void LowLevelCallOnce(absl::once_flag* flag, Callable&& fn, Args&&... args);
+
+// Disables scheduling while on stack when scheduling mode is non-cooperative.
+// No effect for cooperative scheduling modes.
+class SchedulingHelper {
+ public:
+  explicit SchedulingHelper(base_internal::SchedulingMode mode) : mode_(mode) {
+    if (mode_ == base_internal::SCHEDULE_KERNEL_ONLY) {
+      guard_result_ = base_internal::SchedulingGuard::DisableRescheduling();
+    }
+  }
+
+  ~SchedulingHelper() {
+    if (mode_ == base_internal::SCHEDULE_KERNEL_ONLY) {
+      base_internal::SchedulingGuard::EnableRescheduling(guard_result_);
+    }
+  }
+
+ private:
+  base_internal::SchedulingMode mode_;
+  bool guard_result_;
+};
+
+// Bit patterns for call_once state machine values.  Internal implementation
+// detail, not for use by clients.
+//
+// The bit patterns are arbitrarily chosen from unlikely values, to aid in
+// debugging.  However, kOnceInit must be 0, so that a zero-initialized
+// once_flag will be valid for immediate use.
+enum {
+  kOnceInit = 0,
+  kOnceRunning = 0x65C2937B,
+  kOnceWaiter = 0x05A308D2,
+  // A very small constant is chosen for kOnceDone so that it fit in a single
+  // compare with immediate instruction for most common ISAs.  This is verified
+  // for x86, POWER and ARM.
+  kOnceDone = 221,    // Random Number
+};
+
+template <typename Callable, typename... Args>
+ABSL_ATTRIBUTE_NOINLINE
+void CallOnceImpl(std::atomic<uint32_t>* control,
+                  base_internal::SchedulingMode scheduling_mode, Callable&& fn,
+                  Args&&... args) {
+#ifndef NDEBUG
+  {
+    uint32_t old_control = control->load(std::memory_order_relaxed);
+    if (old_control != kOnceInit &&
+        old_control != kOnceRunning &&
+        old_control != kOnceWaiter &&
+        old_control != kOnceDone) {
+      ABSL_RAW_LOG(FATAL, "Unexpected value for control word: 0x%lx",
+                   static_cast<unsigned long>(old_control));  // NOLINT
+    }
+  }
+#endif  // NDEBUG
+  static const base_internal::SpinLockWaitTransition trans[] = {
+      {kOnceInit, kOnceRunning, true},
+      {kOnceRunning, kOnceWaiter, false},
+      {kOnceDone, kOnceDone, true}};
+
+  // Must do this before potentially modifying control word's state.
+  base_internal::SchedulingHelper maybe_disable_scheduling(scheduling_mode);
+  // Short circuit the simplest case to avoid procedure call overhead.
+  // The base_internal::SpinLockWait() call returns either kOnceInit or
+  // kOnceDone. If it returns kOnceDone, it must have loaded the control word
+  // with std::memory_order_acquire and seen a value of kOnceDone.
+  uint32_t old_control = kOnceInit;
+  if (control->compare_exchange_strong(old_control, kOnceRunning,
+                                       std::memory_order_relaxed) ||
+      base_internal::SpinLockWait(control, ABSL_ARRAYSIZE(trans), trans,
+                                  scheduling_mode) == kOnceInit) {
+    base_internal::invoke(std::forward<Callable>(fn),
+                          std::forward<Args>(args)...);
+    old_control =
+        control->exchange(base_internal::kOnceDone, std::memory_order_release);
+    if (old_control == base_internal::kOnceWaiter) {
+      base_internal::SpinLockWake(control, true);
+    }
+  }  // else *control is already kOnceDone
+}
+
+inline std::atomic<uint32_t>* ControlWord(once_flag* flag) {
+  return &flag->control_;
+}
+
+template <typename Callable, typename... Args>
+void LowLevelCallOnce(absl::once_flag* flag, Callable&& fn, Args&&... args) {
+  std::atomic<uint32_t>* once = base_internal::ControlWord(flag);
+  uint32_t s = once->load(std::memory_order_acquire);
+  if (ABSL_PREDICT_FALSE(s != base_internal::kOnceDone)) {
+    base_internal::CallOnceImpl(once, base_internal::SCHEDULE_KERNEL_ONLY,
+                                std::forward<Callable>(fn),
+                                std::forward<Args>(args)...);
+  }
+}
+
+}  // namespace base_internal
+
+template <typename Callable, typename... Args>
+void call_once(absl::once_flag& flag, Callable&& fn, Args&&... args) {
+  std::atomic<uint32_t>* once = base_internal::ControlWord(&flag);
+  uint32_t s = once->load(std::memory_order_acquire);
+  if (ABSL_PREDICT_FALSE(s != base_internal::kOnceDone)) {
+    base_internal::CallOnceImpl(
+        once, base_internal::SCHEDULE_COOPERATIVE_AND_KERNEL,
+        std::forward<Callable>(fn), std::forward<Args>(args)...);
+  }
+}
+
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_BASE_CALL_ONCE_H_
--- a/include/absl/base/casts.h
+++ b/include/absl/base/casts.h
@ -0,0 +1,180 @@
+//
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// -----------------------------------------------------------------------------
+// File: casts.h
+// -----------------------------------------------------------------------------
+//
+// This header file defines casting templates to fit use cases not covered by
+// the standard casts provided in the C++ standard. As with all cast operations,
+// use these with caution and only if alternatives do not exist.
+
+#ifndef ABSL_BASE_CASTS_H_
+#define ABSL_BASE_CASTS_H_
+
+#include <cstring>
+#include <memory>
+#include <type_traits>
+#include <utility>
+
+#if defined(__cpp_lib_bit_cast) && __cpp_lib_bit_cast >= 201806L
+#include <bit>  // For std::bit_cast.
+#endif  // defined(__cpp_lib_bit_cast) && __cpp_lib_bit_cast >= 201806L
+
+#include "absl/base/internal/identity.h"
+#include "absl/base/macros.h"
+#include "absl/meta/type_traits.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+
+// implicit_cast()
+//
+// Performs an implicit conversion between types following the language
+// rules for implicit conversion; if an implicit conversion is otherwise
+// allowed by the language in the given context, this function performs such an
+// implicit conversion.
+//
+// Example:
+//
+//   // If the context allows implicit conversion:
+//   From from;
+//   To to = from;
+//
+//   // Such code can be replaced by:
+//   implicit_cast<To>(from);
+//
+// An `implicit_cast()` may also be used to annotate numeric type conversions
+// that, although safe, may produce compiler warnings (such as `long` to `int`).
+// Additionally, an `implicit_cast()` is also useful within return statements to
+// indicate a specific implicit conversion is being undertaken.
+//
+// Example:
+//
+//   return implicit_cast<double>(size_in_bytes) / capacity_;
+//
+// Annotating code with `implicit_cast()` allows you to explicitly select
+// particular overloads and template instantiations, while providing a safer
+// cast than `reinterpret_cast()` or `static_cast()`.
+//
+// Additionally, an `implicit_cast()` can be used to allow upcasting within a
+// type hierarchy where incorrect use of `static_cast()` could accidentally
+// allow downcasting.
+//
+// Finally, an `implicit_cast()` can be used to perform implicit conversions
+// from unrelated types that otherwise couldn't be implicitly cast directly;
+// C++ will normally only implicitly cast "one step" in such conversions.
+//
+// That is, if C is a type which can be implicitly converted to B, with B being
+// a type that can be implicitly converted to A, an `implicit_cast()` can be
+// used to convert C to B (which the compiler can then implicitly convert to A
+// using language rules).
+//
+// Example:
+//
+//   // Assume an object C is convertible to B, which is implicitly convertible
+//   // to A
+//   A a = implicit_cast<B>(C);
+//
+// Such implicit cast chaining may be useful within template logic.
+template <typename To>
+constexpr To implicit_cast(typename absl::internal::identity_t<To> to) {
+  return to;
+}
+
+// bit_cast()
+//
+// Creates a value of the new type `Dest` whose representation is the same as
+// that of the argument, which is of (deduced) type `Source` (a "bitwise cast";
+// every bit in the value representation of the result is equal to the
+// corresponding bit in the object representation of the source). Source and
+// destination types must be of the same size, and both types must be trivially
+// copyable.
+//
+// As with most casts, use with caution. A `bit_cast()` might be needed when you
+// need to treat a value as the value of some other type, for example, to access
+// the individual bits of an object which are not normally accessible through
+// the object's type, such as for working with the binary representation of a
+// floating point value:
+//
+//   float f = 3.14159265358979;
+//   int i = bit_cast<int>(f);
+//   // i = 0x40490fdb
+//
+// Reinterpreting and accessing a value directly as a different type (as shown
+// below) usually results in undefined behavior.
+//
+// Example:
+//
+//   // WRONG
+//   float f = 3.14159265358979;
+//   int i = reinterpret_cast<int&>(f);    // Wrong
+//   int j = *reinterpret_cast<int*>(&f);  // Equally wrong
+//   int k = *bit_cast<int*>(&f);          // Equally wrong
+//
+// Reinterpret-casting results in undefined behavior according to the ISO C++
+// specification, section [basic.lval]. Roughly, this section says: if an object
+// in memory has one type, and a program accesses it with a different type, the
+// result is undefined behavior for most "different type".
+//
+// Using bit_cast on a pointer and then dereferencing it is no better than using
+// reinterpret_cast. You should only use bit_cast on the value itself.
+//
+// Such casting results in type punning: holding an object in memory of one type
+// and reading its bits back using a different type. A `bit_cast()` avoids this
+// issue by copying the object representation to a new value, which avoids
+// introducing this undefined behavior (since the original value is never
+// accessed in the wrong way).
+//
+// The requirements of `absl::bit_cast` are more strict than that of
+// `std::bit_cast` unless compiler support is available. Specifically, without
+// compiler support, this implementation also requires `Dest` to be
+// default-constructible. In C++20, `absl::bit_cast` is replaced by
+// `std::bit_cast`.
+#if defined(__cpp_lib_bit_cast) && __cpp_lib_bit_cast >= 201806L
+
+using std::bit_cast;
+
+#else  // defined(__cpp_lib_bit_cast) && __cpp_lib_bit_cast >= 201806L
+
+template <typename Dest, typename Source,
+          typename std::enable_if<
+              sizeof(Dest) == sizeof(Source) &&
+                  type_traits_internal::is_trivially_copyable<Source>::value &&
+                  type_traits_internal::is_trivially_copyable<Dest>::value
+#if !ABSL_HAVE_BUILTIN(__builtin_bit_cast)
+                  && std::is_default_constructible<Dest>::value
+#endif  // !ABSL_HAVE_BUILTIN(__builtin_bit_cast)
+              ,
+              int>::type = 0>
+#if ABSL_HAVE_BUILTIN(__builtin_bit_cast)
+inline constexpr Dest bit_cast(const Source& source) {
+  return __builtin_bit_cast(Dest, source);
+}
+#else  // ABSL_HAVE_BUILTIN(__builtin_bit_cast)
+inline Dest bit_cast(const Source& source) {
+  Dest dest;
+  memcpy(static_cast<void*>(std::addressof(dest)),
+         static_cast<const void*>(std::addressof(source)), sizeof(dest));
+  return dest;
+}
+#endif  // ABSL_HAVE_BUILTIN(__builtin_bit_cast)
+
+#endif  // defined(__cpp_lib_bit_cast) && __cpp_lib_bit_cast >= 201806L
+
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_BASE_CASTS_H_
--- a/include/absl/base/config.h
+++ b/include/absl/base/config.h
@ -0,0 +1,913 @@
+//
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// -----------------------------------------------------------------------------
+// File: config.h
+// -----------------------------------------------------------------------------
+//
+// This header file defines a set of macros for checking the presence of
+// important compiler and platform features. Such macros can be used to
+// produce portable code by parameterizing compilation based on the presence or
+// lack of a given feature.
+//
+// We define a "feature" as some interface we wish to program to: for example,
+// a library function or system call. A value of `1` indicates support for
+// that feature; any other value indicates the feature support is undefined.
+//
+// Example:
+//
+// Suppose a programmer wants to write a program that uses the 'mmap()' system
+// call. The Abseil macro for that feature (`ABSL_HAVE_MMAP`) allows you to
+// selectively include the `mmap.h` header and bracket code using that feature
+// in the macro:
+//
+//   #include "absl/base/config.h"
+//
+//   #ifdef ABSL_HAVE_MMAP
+//   #include "sys/mman.h"
+//   #endif  //ABSL_HAVE_MMAP
+//
+//   ...
+//   #ifdef ABSL_HAVE_MMAP
+//   void *ptr = mmap(...);
+//   ...
+//   #endif  // ABSL_HAVE_MMAP
+
+#ifndef ABSL_BASE_CONFIG_H_
+#define ABSL_BASE_CONFIG_H_
+
+// Included for the __GLIBC__ macro (or similar macros on other systems).
+#include <limits.h>
+
+#ifdef __cplusplus
+// Included for __GLIBCXX__, _LIBCPP_VERSION
+#include <cstddef>
+#endif  // __cplusplus
+
+// ABSL_INTERNAL_CPLUSPLUS_LANG
+//
+// MSVC does not set the value of __cplusplus correctly, but instead uses
+// _MSVC_LANG as a stand-in.
+// https://docs.microsoft.com/en-us/cpp/preprocessor/predefined-macros
+//
+// However, there are reports that MSVC even sets _MSVC_LANG incorrectly at
+// times, for example:
+// https://github.com/microsoft/vscode-cpptools/issues/1770
+// https://reviews.llvm.org/D70996
+//
+// For this reason, this symbol is considered INTERNAL and code outside of
+// Abseil must not use it.
+#if defined(_MSVC_LANG)
+#define ABSL_INTERNAL_CPLUSPLUS_LANG _MSVC_LANG
+#elif defined(__cplusplus)
+#define ABSL_INTERNAL_CPLUSPLUS_LANG __cplusplus
+#endif
+
+#if defined(__APPLE__)
+// Included for TARGET_OS_IPHONE, __IPHONE_OS_VERSION_MIN_REQUIRED,
+// __IPHONE_8_0.
+#include <Availability.h>
+#include <TargetConditionals.h>
+#endif
+
+#include "absl/base/options.h"
+#include "absl/base/policy_checks.h"
+
+// Abseil long-term support (LTS) releases will define
+// `ABSL_LTS_RELEASE_VERSION` to the integer representing the date string of the
+// LTS release version, and will define `ABSL_LTS_RELEASE_PATCH_LEVEL` to the
+// integer representing the patch-level for that release.
+//
+// For example, for LTS release version "20300401.2", this would give us
+// ABSL_LTS_RELEASE_VERSION == 20300401 && ABSL_LTS_RELEASE_PATCH_LEVEL == 2
+//
+// These symbols will not be defined in non-LTS code.
+//
+// Abseil recommends that clients live-at-head. Therefore, if you are using
+// these symbols to assert a minimum version requirement, we recommend you do it
+// as
+//
+// #if defined(ABSL_LTS_RELEASE_VERSION) && ABSL_LTS_RELEASE_VERSION < 20300401
+// #error Project foo requires Abseil LTS version >= 20300401
+// #endif
+//
+// The `defined(ABSL_LTS_RELEASE_VERSION)` part of the check excludes
+// live-at-head clients from the minimum version assertion.
+//
+// See https://abseil.io/about/releases for more information on Abseil release
+// management.
+//
+// LTS releases can be obtained from
+// https://github.com/abseil/abseil-cpp/releases.
+#define ABSL_LTS_RELEASE_VERSION 20220623
+#define ABSL_LTS_RELEASE_PATCH_LEVEL 0
+
+// Helper macro to convert a CPP variable to a string literal.
+#define ABSL_INTERNAL_DO_TOKEN_STR(x) #x
+#define ABSL_INTERNAL_TOKEN_STR(x) ABSL_INTERNAL_DO_TOKEN_STR(x)
+
+// -----------------------------------------------------------------------------
+// Abseil namespace annotations
+// -----------------------------------------------------------------------------
+
+// ABSL_NAMESPACE_BEGIN/ABSL_NAMESPACE_END
+//
+// An annotation placed at the beginning/end of each `namespace absl` scope.
+// This is used to inject an inline namespace.
+//
+// The proper way to write Abseil code in the `absl` namespace is:
+//
+// namespace absl {
+// ABSL_NAMESPACE_BEGIN
+//
+// void Foo();  // absl::Foo().
+//
+// ABSL_NAMESPACE_END
+// }  // namespace absl
+//
+// Users of Abseil should not use these macros, because users of Abseil should
+// not write `namespace absl {` in their own code for any reason.  (Abseil does
+// not support forward declarations of its own types, nor does it support
+// user-provided specialization of Abseil templates.  Code that violates these
+// rules may be broken without warning.)
+#if !defined(ABSL_OPTION_USE_INLINE_NAMESPACE) || \
+    !defined(ABSL_OPTION_INLINE_NAMESPACE_NAME)
+#error options.h is misconfigured.
+#endif
+
+// Check that ABSL_OPTION_INLINE_NAMESPACE_NAME is neither "head" nor ""
+#if defined(__cplusplus) && ABSL_OPTION_USE_INLINE_NAMESPACE == 1
+
+#define ABSL_INTERNAL_INLINE_NAMESPACE_STR \
+  ABSL_INTERNAL_TOKEN_STR(ABSL_OPTION_INLINE_NAMESPACE_NAME)
+
+static_assert(ABSL_INTERNAL_INLINE_NAMESPACE_STR[0] != '\0',
+              "options.h misconfigured: ABSL_OPTION_INLINE_NAMESPACE_NAME must "
+              "not be empty.");
+static_assert(ABSL_INTERNAL_INLINE_NAMESPACE_STR[0] != 'h' ||
+                  ABSL_INTERNAL_INLINE_NAMESPACE_STR[1] != 'e' ||
+                  ABSL_INTERNAL_INLINE_NAMESPACE_STR[2] != 'a' ||
+                  ABSL_INTERNAL_INLINE_NAMESPACE_STR[3] != 'd' ||
+                  ABSL_INTERNAL_INLINE_NAMESPACE_STR[4] != '\0',
+              "options.h misconfigured: ABSL_OPTION_INLINE_NAMESPACE_NAME must "
+              "be changed to a new, unique identifier name.");
+
+#endif
+
+#if ABSL_OPTION_USE_INLINE_NAMESPACE == 0
+#define ABSL_NAMESPACE_BEGIN
+#define ABSL_NAMESPACE_END
+#define ABSL_INTERNAL_C_SYMBOL(x) x
+#elif ABSL_OPTION_USE_INLINE_NAMESPACE == 1
+#define ABSL_NAMESPACE_BEGIN \
+  inline namespace ABSL_OPTION_INLINE_NAMESPACE_NAME {
+#define ABSL_NAMESPACE_END }
+#define ABSL_INTERNAL_C_SYMBOL_HELPER_2(x, v) x##_##v
+#define ABSL_INTERNAL_C_SYMBOL_HELPER_1(x, v) \
+  ABSL_INTERNAL_C_SYMBOL_HELPER_2(x, v)
+#define ABSL_INTERNAL_C_SYMBOL(x) \
+  ABSL_INTERNAL_C_SYMBOL_HELPER_1(x, ABSL_OPTION_INLINE_NAMESPACE_NAME)
+#else
+#error options.h is misconfigured.
+#endif
+
+// -----------------------------------------------------------------------------
+// Compiler Feature Checks
+// -----------------------------------------------------------------------------
+
+// ABSL_HAVE_BUILTIN()
+//
+// Checks whether the compiler supports a Clang Feature Checking Macro, and if
+// so, checks whether it supports the provided builtin function "x" where x
+// is one of the functions noted in
+// https://clang.llvm.org/docs/LanguageExtensions.html
+//
+// Note: Use this macro to avoid an extra level of #ifdef __has_builtin check.
+// http://releases.llvm.org/3.3/tools/clang/docs/LanguageExtensions.html
+#ifdef __has_builtin
+#define ABSL_HAVE_BUILTIN(x) __has_builtin(x)
+#else
+#define ABSL_HAVE_BUILTIN(x) 0
+#endif
+
+#ifdef __has_feature
+#define ABSL_HAVE_FEATURE(f) __has_feature(f)
+#else
+#define ABSL_HAVE_FEATURE(f) 0
+#endif
+
+// Portable check for GCC minimum version:
+// https://gcc.gnu.org/onlinedocs/cpp/Common-Predefined-Macros.html
+#if defined(__GNUC__) && defined(__GNUC_MINOR__)
+#define ABSL_INTERNAL_HAVE_MIN_GNUC_VERSION(x, y) \
+  (__GNUC__ > (x) || __GNUC__ == (x) && __GNUC_MINOR__ >= (y))
+#else
+#define ABSL_INTERNAL_HAVE_MIN_GNUC_VERSION(x, y) 0
+#endif
+
+#if defined(__clang__) && defined(__clang_major__) && defined(__clang_minor__)
+#define ABSL_INTERNAL_HAVE_MIN_CLANG_VERSION(x, y) \
+  (__clang_major__ > (x) || __clang_major__ == (x) && __clang_minor__ >= (y))
+#else
+#define ABSL_INTERNAL_HAVE_MIN_CLANG_VERSION(x, y) 0
+#endif
+
+// ABSL_HAVE_TLS is defined to 1 when __thread should be supported.
+// We assume __thread is supported on Linux or Asylo when compiled with Clang or
+// compiled against libstdc++ with _GLIBCXX_HAVE_TLS defined.
+#ifdef ABSL_HAVE_TLS
+#error ABSL_HAVE_TLS cannot be directly set
+#elif (defined(__linux__) || defined(__ASYLO__)) && \
+    (defined(__clang__) || defined(_GLIBCXX_HAVE_TLS))
+#define ABSL_HAVE_TLS 1
+#endif
+
+// ABSL_HAVE_STD_IS_TRIVIALLY_DESTRUCTIBLE
+//
+// Checks whether `std::is_trivially_destructible<T>` is supported.
+//
+// Notes: All supported compilers using libc++ support this feature, as does
+// gcc >= 4.8.1 using libstdc++, and Visual Studio.
+#ifdef ABSL_HAVE_STD_IS_TRIVIALLY_DESTRUCTIBLE
+#error ABSL_HAVE_STD_IS_TRIVIALLY_DESTRUCTIBLE cannot be directly set
+#elif defined(_LIBCPP_VERSION) || defined(_MSC_VER) || \
+    (!defined(__clang__) && defined(__GLIBCXX__) &&    \
+     ABSL_INTERNAL_HAVE_MIN_GNUC_VERSION(4, 8))
+#define ABSL_HAVE_STD_IS_TRIVIALLY_DESTRUCTIBLE 1
+#endif
+
+// ABSL_HAVE_STD_IS_TRIVIALLY_CONSTRUCTIBLE
+//
+// Checks whether `std::is_trivially_default_constructible<T>` and
+// `std::is_trivially_copy_constructible<T>` are supported.
+
+// ABSL_HAVE_STD_IS_TRIVIALLY_ASSIGNABLE
+//
+// Checks whether `std::is_trivially_copy_assignable<T>` is supported.
+
+// Notes: Clang with libc++ supports these features, as does gcc >= 7.4 with
+// libstdc++, or gcc >= 8.2 with libc++, and Visual Studio (but not NVCC).
+#if defined(ABSL_HAVE_STD_IS_TRIVIALLY_CONSTRUCTIBLE)
+#error ABSL_HAVE_STD_IS_TRIVIALLY_CONSTRUCTIBLE cannot be directly set
+#elif defined(ABSL_HAVE_STD_IS_TRIVIALLY_ASSIGNABLE)
+#error ABSL_HAVE_STD_IS_TRIVIALLY_ASSIGNABLE cannot directly set
+#elif (defined(__clang__) && defined(_LIBCPP_VERSION)) ||                    \
+    (!defined(__clang__) &&                                                  \
+     ((ABSL_INTERNAL_HAVE_MIN_GNUC_VERSION(7, 4) && defined(__GLIBCXX__)) || \
+      (ABSL_INTERNAL_HAVE_MIN_GNUC_VERSION(8, 2) &&                          \
+       defined(_LIBCPP_VERSION)))) ||                                        \
+    (defined(_MSC_VER) && !defined(__NVCC__))
+#define ABSL_HAVE_STD_IS_TRIVIALLY_CONSTRUCTIBLE 1
+#define ABSL_HAVE_STD_IS_TRIVIALLY_ASSIGNABLE 1
+#endif
+
+// ABSL_HAVE_THREAD_LOCAL
+//
+// Checks whether C++11's `thread_local` storage duration specifier is
+// supported.
+#ifdef ABSL_HAVE_THREAD_LOCAL
+#error ABSL_HAVE_THREAD_LOCAL cannot be directly set
+#elif defined(__APPLE__)
+// Notes:
+// * Xcode's clang did not support `thread_local` until version 8, and
+//   even then not for all iOS < 9.0.
+// * Xcode 9.3 started disallowing `thread_local` for 32-bit iOS simulator
+//   targeting iOS 9.x.
+// * Xcode 10 moves the deployment target check for iOS < 9.0 to link time
+//   making ABSL_HAVE_FEATURE unreliable there.
+//
+#if ABSL_HAVE_FEATURE(cxx_thread_local) && \
+    !(TARGET_OS_IPHONE && __IPHONE_OS_VERSION_MIN_REQUIRED < __IPHONE_9_0)
+#define ABSL_HAVE_THREAD_LOCAL 1
+#endif
+#else  // !defined(__APPLE__)
+#define ABSL_HAVE_THREAD_LOCAL 1
+#endif
+
+// There are platforms for which TLS should not be used even though the compiler
+// makes it seem like it's supported (Android NDK < r12b for example).
+// This is primarily because of linker problems and toolchain misconfiguration:
+// Abseil does not intend to support this indefinitely. Currently, the newest
+// toolchain that we intend to support that requires this behavior is the
+// r11 NDK - allowing for a 5 year support window on that means this option
+// is likely to be removed around June of 2021.
+// TLS isn't supported until NDK r12b per
+// https://developer.android.com/ndk/downloads/revision_history.html
+// Since NDK r16, `__NDK_MAJOR__` and `__NDK_MINOR__` are defined in
+// <android/ndk-version.h>. For NDK < r16, users should define these macros,
+// e.g. `-D__NDK_MAJOR__=11 -D__NKD_MINOR__=0` for NDK r11.
+#if defined(__ANDROID__) && defined(__clang__)
+#if __has_include(<android/ndk-version.h>)
+#include <android/ndk-version.h>
+#endif  // __has_include(<android/ndk-version.h>)
+#if defined(__ANDROID__) && defined(__clang__) && defined(__NDK_MAJOR__) && \
+    defined(__NDK_MINOR__) &&                                               \
+    ((__NDK_MAJOR__ < 12) || ((__NDK_MAJOR__ == 12) && (__NDK_MINOR__ < 1)))
+#undef ABSL_HAVE_TLS
+#undef ABSL_HAVE_THREAD_LOCAL
+#endif
+#endif  // defined(__ANDROID__) && defined(__clang__)
+
+// ABSL_HAVE_INTRINSIC_INT128
+//
+// Checks whether the __int128 compiler extension for a 128-bit integral type is
+// supported.
+//
+// Note: __SIZEOF_INT128__ is defined by Clang and GCC when __int128 is
+// supported, but we avoid using it in certain cases:
+// * On Clang:
+//   * Building using Clang for Windows, where the Clang runtime library has
+//     128-bit support only on LP64 architectures, but Windows is LLP64.
+// * On Nvidia's nvcc:
+//   * nvcc also defines __GNUC__ and __SIZEOF_INT128__, but not all versions
+//     actually support __int128.
+#ifdef ABSL_HAVE_INTRINSIC_INT128
+#error ABSL_HAVE_INTRINSIC_INT128 cannot be directly set
+#elif defined(__SIZEOF_INT128__)
+#if (defined(__clang__) && !defined(_WIN32)) || \
+    (defined(__CUDACC__) && __CUDACC_VER_MAJOR__ >= 9) ||                \
+    (defined(__GNUC__) && !defined(__clang__) && !defined(__CUDACC__))
+#define ABSL_HAVE_INTRINSIC_INT128 1
+#elif defined(__CUDACC__)
+// __CUDACC_VER__ is a full version number before CUDA 9, and is defined to a
+// string explaining that it has been removed starting with CUDA 9. We use
+// nested #ifs because there is no short-circuiting in the preprocessor.
+// NOTE: `__CUDACC__` could be undefined while `__CUDACC_VER__` is defined.
+#if __CUDACC_VER__ >= 70000
+#define ABSL_HAVE_INTRINSIC_INT128 1
+#endif  // __CUDACC_VER__ >= 70000
+#endif  // defined(__CUDACC__)
+#endif  // ABSL_HAVE_INTRINSIC_INT128
+
+// ABSL_HAVE_EXCEPTIONS
+//
+// Checks whether the compiler both supports and enables exceptions. Many
+// compilers support a "no exceptions" mode that disables exceptions.
+//
+// Generally, when ABSL_HAVE_EXCEPTIONS is not defined:
+//
+// * Code using `throw` and `try` may not compile.
+// * The `noexcept` specifier will still compile and behave as normal.
+// * The `noexcept` operator may still return `false`.
+//
+// For further details, consult the compiler's documentation.
+#ifdef ABSL_HAVE_EXCEPTIONS
+#error ABSL_HAVE_EXCEPTIONS cannot be directly set.
+#elif ABSL_INTERNAL_HAVE_MIN_CLANG_VERSION(3, 6)
+// Clang >= 3.6
+#if ABSL_HAVE_FEATURE(cxx_exceptions)
+#define ABSL_HAVE_EXCEPTIONS 1
+#endif  // ABSL_HAVE_FEATURE(cxx_exceptions)
+#elif defined(__clang__)
+// Clang < 3.6
+// http://releases.llvm.org/3.6.0/tools/clang/docs/ReleaseNotes.html#the-exceptions-macro
+#if defined(__EXCEPTIONS) && ABSL_HAVE_FEATURE(cxx_exceptions)
+#define ABSL_HAVE_EXCEPTIONS 1
+#endif  // defined(__EXCEPTIONS) && ABSL_HAVE_FEATURE(cxx_exceptions)
+// Handle remaining special cases and default to exceptions being supported.
+#elif !(defined(__GNUC__) && (__GNUC__ < 5) && !defined(__EXCEPTIONS)) && \
+    !(ABSL_INTERNAL_HAVE_MIN_GNUC_VERSION(5, 0) &&                        \
+      !defined(__cpp_exceptions)) &&                                      \
+    !(defined(_MSC_VER) && !defined(_CPPUNWIND))
+#define ABSL_HAVE_EXCEPTIONS 1
+#endif
+
+// -----------------------------------------------------------------------------
+// Platform Feature Checks
+// -----------------------------------------------------------------------------
+
+// Currently supported operating systems and associated preprocessor
+// symbols:
+//
+//   Linux and Linux-derived           __linux__
+//   Android                           __ANDROID__ (implies __linux__)
+//   Linux (non-Android)               __linux__ && !__ANDROID__
+//   Darwin (macOS and iOS)            __APPLE__
+//   Akaros (http://akaros.org)        __ros__
+//   Windows                           _WIN32
+//   NaCL                              __native_client__
+//   AsmJS                             __asmjs__
+//   WebAssembly                       __wasm__
+//   Fuchsia                           __Fuchsia__
+//
+// Note that since Android defines both __ANDROID__ and __linux__, one
+// may probe for either Linux or Android by simply testing for __linux__.
+
+// ABSL_HAVE_MMAP
+//
+// Checks whether the platform has an mmap(2) implementation as defined in
+// POSIX.1-2001.
+#ifdef ABSL_HAVE_MMAP
+#error ABSL_HAVE_MMAP cannot be directly set
+#elif defined(__linux__) || defined(__APPLE__) || defined(__FreeBSD__) || \
+    defined(_AIX) || defined(__ros__) || defined(__native_client__) ||    \
+    defined(__asmjs__) || defined(__wasm__) || defined(__Fuchsia__) ||    \
+    defined(__sun) || defined(__ASYLO__) || defined(__myriad2__) ||       \
+    defined(__HAIKU__) || defined(__OpenBSD__) || defined(__NetBSD__) ||  \
+    defined(__QNX__)
+#define ABSL_HAVE_MMAP 1
+#endif
+
+// ABSL_HAVE_PTHREAD_GETSCHEDPARAM
+//
+// Checks whether the platform implements the pthread_(get|set)schedparam(3)
+// functions as defined in POSIX.1-2001.
+#ifdef ABSL_HAVE_PTHREAD_GETSCHEDPARAM
+#error ABSL_HAVE_PTHREAD_GETSCHEDPARAM cannot be directly set
+#elif defined(__linux__) || defined(__APPLE__) || defined(__FreeBSD__) || \
+    defined(_AIX) || defined(__ros__) || defined(__OpenBSD__) ||          \
+    defined(__NetBSD__)
+#define ABSL_HAVE_PTHREAD_GETSCHEDPARAM 1
+#endif
+
+// ABSL_HAVE_SCHED_GETCPU
+//
+// Checks whether sched_getcpu is available.
+#ifdef ABSL_HAVE_SCHED_GETCPU
+#error ABSL_HAVE_SCHED_GETCPU cannot be directly set
+#elif defined(__linux__)
+#define ABSL_HAVE_SCHED_GETCPU 1
+#endif
+
+// ABSL_HAVE_SCHED_YIELD
+//
+// Checks whether the platform implements sched_yield(2) as defined in
+// POSIX.1-2001.
+#ifdef ABSL_HAVE_SCHED_YIELD
+#error ABSL_HAVE_SCHED_YIELD cannot be directly set
+#elif defined(__linux__) || defined(__ros__) || defined(__native_client__)
+#define ABSL_HAVE_SCHED_YIELD 1
+#endif
+
+// ABSL_HAVE_SEMAPHORE_H
+//
+// Checks whether the platform supports the <semaphore.h> header and sem_init(3)
+// family of functions as standardized in POSIX.1-2001.
+//
+// Note: While Apple provides <semaphore.h> for both iOS and macOS, it is
+// explicitly deprecated and will cause build failures if enabled for those
+// platforms.  We side-step the issue by not defining it here for Apple
+// platforms.
+#ifdef ABSL_HAVE_SEMAPHORE_H
+#error ABSL_HAVE_SEMAPHORE_H cannot be directly set
+#elif defined(__linux__) || defined(__ros__)
+#define ABSL_HAVE_SEMAPHORE_H 1
+#endif
+
+// ABSL_HAVE_ALARM
+//
+// Checks whether the platform supports the <signal.h> header and alarm(2)
+// function as standardized in POSIX.1-2001.
+#ifdef ABSL_HAVE_ALARM
+#error ABSL_HAVE_ALARM cannot be directly set
+#elif defined(__GOOGLE_GRTE_VERSION__)
+// feature tests for Google's GRTE
+#define ABSL_HAVE_ALARM 1
+#elif defined(__GLIBC__)
+// feature test for glibc
+#define ABSL_HAVE_ALARM 1
+#elif defined(_MSC_VER)
+// feature tests for Microsoft's library
+#elif defined(__MINGW32__)
+// mingw32 doesn't provide alarm(2):
+// https://osdn.net/projects/mingw/scm/git/mingw-org-wsl/blobs/5.2-trunk/mingwrt/include/unistd.h
+// mingw-w64 provides a no-op implementation:
+// https://sourceforge.net/p/mingw-w64/mingw-w64/ci/master/tree/mingw-w64-crt/misc/alarm.c
+#elif defined(__EMSCRIPTEN__)
+// emscripten doesn't support signals
+#elif defined(__Fuchsia__)
+// Signals don't exist on fuchsia.
+#elif defined(__native_client__)
+#else
+// other standard libraries
+#define ABSL_HAVE_ALARM 1
+#endif
+
+// ABSL_IS_LITTLE_ENDIAN
+// ABSL_IS_BIG_ENDIAN
+//
+// Checks the endianness of the platform.
+//
+// Notes: uses the built in endian macros provided by GCC (since 4.6) and
+// Clang (since 3.2); see
+// https://gcc.gnu.org/onlinedocs/cpp/Common-Predefined-Macros.html.
+// Otherwise, if _WIN32, assume little endian. Otherwise, bail with an error.
+#if defined(ABSL_IS_BIG_ENDIAN)
+#error "ABSL_IS_BIG_ENDIAN cannot be directly set."
+#endif
+#if defined(ABSL_IS_LITTLE_ENDIAN)
+#error "ABSL_IS_LITTLE_ENDIAN cannot be directly set."
+#endif
+
+#if (defined(__BYTE_ORDER__) && defined(__ORDER_LITTLE_ENDIAN__) && \
+     __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__)
+#define ABSL_IS_LITTLE_ENDIAN 1
+#elif defined(__BYTE_ORDER__) && defined(__ORDER_BIG_ENDIAN__) && \
+    __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
+#define ABSL_IS_BIG_ENDIAN 1
+#elif defined(_WIN32)
+#define ABSL_IS_LITTLE_ENDIAN 1
+#else
+#error "absl endian detection needs to be set up for your compiler"
+#endif
+
+// macOS < 10.13 and iOS < 11 don't let you use <any>, <optional>, or <variant>
+// even though the headers exist and are publicly noted to work, because the
+// libc++ shared library shipped on the system doesn't have the requisite
+// exported symbols.  See https://github.com/abseil/abseil-cpp/issues/207 and
+// https://developer.apple.com/documentation/xcode_release_notes/xcode_10_release_notes
+//
+// libc++ spells out the availability requirements in the file
+// llvm-project/libcxx/include/__config via the #define
+// _LIBCPP_AVAILABILITY_BAD_OPTIONAL_ACCESS.
+//
+// Unfortunately, Apple initially mis-stated the requirements as macOS < 10.14
+// and iOS < 12 in the libc++ headers. This was corrected by
+// https://github.com/llvm/llvm-project/commit/7fb40e1569dd66292b647f4501b85517e9247953
+// which subsequently made it into the XCode 12.5 release. We need to match the
+// old (incorrect) conditions when built with old XCode, but can use the
+// corrected earlier versions with new XCode.
+#if defined(__APPLE__) && defined(_LIBCPP_VERSION) &&               \
+    ((_LIBCPP_VERSION >= 11000 && /* XCode 12.5 or later: */        \
+      ((defined(__ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__) &&   \
+        __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ < 101300) ||  \
+       (defined(__ENVIRONMENT_IPHONE_OS_VERSION_MIN_REQUIRED__) &&  \
+        __ENVIRONMENT_IPHONE_OS_VERSION_MIN_REQUIRED__ < 110000) || \
+       (defined(__ENVIRONMENT_WATCH_OS_VERSION_MIN_REQUIRED__) &&   \
+        __ENVIRONMENT_WATCH_OS_VERSION_MIN_REQUIRED__ < 40000) ||   \
+       (defined(__ENVIRONMENT_TV_OS_VERSION_MIN_REQUIRED__) &&      \
+        __ENVIRONMENT_TV_OS_VERSION_MIN_REQUIRED__ < 110000))) ||   \
+     (_LIBCPP_VERSION < 11000 && /* Pre-XCode 12.5: */              \
+      ((defined(__ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__) &&   \
+        __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ < 101400) ||  \
+       (defined(__ENVIRONMENT_IPHONE_OS_VERSION_MIN_REQUIRED__) &&  \
+        __ENVIRONMENT_IPHONE_OS_VERSION_MIN_REQUIRED__ < 120000) || \
+       (defined(__ENVIRONMENT_WATCH_OS_VERSION_MIN_REQUIRED__) &&   \
+        __ENVIRONMENT_WATCH_OS_VERSION_MIN_REQUIRED__ < 50000) ||   \
+       (defined(__ENVIRONMENT_TV_OS_VERSION_MIN_REQUIRED__) &&      \
+        __ENVIRONMENT_TV_OS_VERSION_MIN_REQUIRED__ < 120000))))
+#define ABSL_INTERNAL_APPLE_CXX17_TYPES_UNAVAILABLE 1
+#else
+#define ABSL_INTERNAL_APPLE_CXX17_TYPES_UNAVAILABLE 0
+#endif
+
+// ABSL_HAVE_STD_ANY
+//
+// Checks whether C++17 std::any is available by checking whether <any> exists.
+#ifdef ABSL_HAVE_STD_ANY
+#error "ABSL_HAVE_STD_ANY cannot be directly set."
+#endif
+
+#ifdef __has_include
+#if __has_include(<any>) && defined(__cplusplus) && __cplusplus >= 201703L && \
+    !ABSL_INTERNAL_APPLE_CXX17_TYPES_UNAVAILABLE
+#define ABSL_HAVE_STD_ANY 1
+#endif
+#endif
+
+// ABSL_HAVE_STD_OPTIONAL
+//
+// Checks whether C++17 std::optional is available.
+#ifdef ABSL_HAVE_STD_OPTIONAL
+#error "ABSL_HAVE_STD_OPTIONAL cannot be directly set."
+#endif
+
+#ifdef __has_include
+#if __has_include(<optional>) && defined(__cplusplus) && \
+    __cplusplus >= 201703L && !ABSL_INTERNAL_APPLE_CXX17_TYPES_UNAVAILABLE
+#define ABSL_HAVE_STD_OPTIONAL 1
+#endif
+#endif
+
+// ABSL_HAVE_STD_VARIANT
+//
+// Checks whether C++17 std::variant is available.
+#ifdef ABSL_HAVE_STD_VARIANT
+#error "ABSL_HAVE_STD_VARIANT cannot be directly set."
+#endif
+
+#ifdef __has_include
+#if __has_include(<variant>) && defined(__cplusplus) && \
+    __cplusplus >= 201703L && !ABSL_INTERNAL_APPLE_CXX17_TYPES_UNAVAILABLE
+#define ABSL_HAVE_STD_VARIANT 1
+#endif
+#endif
+
+// ABSL_HAVE_STD_STRING_VIEW
+//
+// Checks whether C++17 std::string_view is available.
+#ifdef ABSL_HAVE_STD_STRING_VIEW
+#error "ABSL_HAVE_STD_STRING_VIEW cannot be directly set."
+#endif
+
+#ifdef __has_include
+#if __has_include(<string_view>) && defined(__cplusplus) && \
+    __cplusplus >= 201703L
+#define ABSL_HAVE_STD_STRING_VIEW 1
+#endif
+#endif
+
+// For MSVC, `__has_include` is supported in VS 2017 15.3, which is later than
+// the support for <optional>, <any>, <string_view>, <variant>. So we use
+// _MSC_VER to check whether we have VS 2017 RTM (when <optional>, <any>,
+// <string_view>, <variant> is implemented) or higher. Also, `__cplusplus` is
+// not correctly set by MSVC, so we use `_MSVC_LANG` to check the language
+// version.
+// TODO(zhangxy): fix tests before enabling aliasing for `std::any`.
+#if defined(_MSC_VER) && _MSC_VER >= 1910 &&         \
+    ((defined(_MSVC_LANG) && _MSVC_LANG > 201402) || \
+     (defined(__cplusplus) && __cplusplus > 201402))
+// #define ABSL_HAVE_STD_ANY 1
+#define ABSL_HAVE_STD_OPTIONAL 1
+#define ABSL_HAVE_STD_VARIANT 1
+#define ABSL_HAVE_STD_STRING_VIEW 1
+#endif
+
+// ABSL_USES_STD_ANY
+//
+// Indicates whether absl::any is an alias for std::any.
+#if !defined(ABSL_OPTION_USE_STD_ANY)
+#error options.h is misconfigured.
+#elif ABSL_OPTION_USE_STD_ANY == 0 || \
+    (ABSL_OPTION_USE_STD_ANY == 2 && !defined(ABSL_HAVE_STD_ANY))
+#undef ABSL_USES_STD_ANY
+#elif ABSL_OPTION_USE_STD_ANY == 1 || \
+    (ABSL_OPTION_USE_STD_ANY == 2 && defined(ABSL_HAVE_STD_ANY))
+#define ABSL_USES_STD_ANY 1
+#else
+#error options.h is misconfigured.
+#endif
+
+// ABSL_USES_STD_OPTIONAL
+//
+// Indicates whether absl::optional is an alias for std::optional.
+#if !defined(ABSL_OPTION_USE_STD_OPTIONAL)
+#error options.h is misconfigured.
+#elif ABSL_OPTION_USE_STD_OPTIONAL == 0 || \
+    (ABSL_OPTION_USE_STD_OPTIONAL == 2 && !defined(ABSL_HAVE_STD_OPTIONAL))
+#undef ABSL_USES_STD_OPTIONAL
+#elif ABSL_OPTION_USE_STD_OPTIONAL == 1 || \
+    (ABSL_OPTION_USE_STD_OPTIONAL == 2 && defined(ABSL_HAVE_STD_OPTIONAL))
+#define ABSL_USES_STD_OPTIONAL 1
+#else
+#error options.h is misconfigured.
+#endif
+
+// ABSL_USES_STD_VARIANT
+//
+// Indicates whether absl::variant is an alias for std::variant.
+#if !defined(ABSL_OPTION_USE_STD_VARIANT)
+#error options.h is misconfigured.
+#elif ABSL_OPTION_USE_STD_VARIANT == 0 || \
+    (ABSL_OPTION_USE_STD_VARIANT == 2 && !defined(ABSL_HAVE_STD_VARIANT))
+#undef ABSL_USES_STD_VARIANT
+#elif ABSL_OPTION_USE_STD_VARIANT == 1 || \
+    (ABSL_OPTION_USE_STD_VARIANT == 2 && defined(ABSL_HAVE_STD_VARIANT))
+#define ABSL_USES_STD_VARIANT 1
+#else
+#error options.h is misconfigured.
+#endif
+
+// ABSL_USES_STD_STRING_VIEW
+//
+// Indicates whether absl::string_view is an alias for std::string_view.
+#if !defined(ABSL_OPTION_USE_STD_STRING_VIEW)
+#error options.h is misconfigured.
+#elif ABSL_OPTION_USE_STD_STRING_VIEW == 0 || \
+    (ABSL_OPTION_USE_STD_STRING_VIEW == 2 &&  \
+     !defined(ABSL_HAVE_STD_STRING_VIEW))
+#undef ABSL_USES_STD_STRING_VIEW
+#elif ABSL_OPTION_USE_STD_STRING_VIEW == 1 || \
+    (ABSL_OPTION_USE_STD_STRING_VIEW == 2 &&  \
+     defined(ABSL_HAVE_STD_STRING_VIEW))
+#define ABSL_USES_STD_STRING_VIEW 1
+#else
+#error options.h is misconfigured.
+#endif
+
+// In debug mode, MSVC 2017's std::variant throws a EXCEPTION_ACCESS_VIOLATION
+// SEH exception from emplace for variant<SomeStruct> when constructing the
+// struct can throw. This defeats some of variant_test and
+// variant_exception_safety_test.
+#if defined(_MSC_VER) && _MSC_VER >= 1700 && defined(_DEBUG)
+#define ABSL_INTERNAL_MSVC_2017_DBG_MODE
+#endif
+
+// ABSL_INTERNAL_MANGLED_NS
+// ABSL_INTERNAL_MANGLED_BACKREFERENCE
+//
+// Internal macros for building up mangled names in our internal fork of CCTZ.
+// This implementation detail is only needed and provided for the MSVC build.
+//
+// These macros both expand to string literals.  ABSL_INTERNAL_MANGLED_NS is
+// the mangled spelling of the `absl` namespace, and
+// ABSL_INTERNAL_MANGLED_BACKREFERENCE is a back-reference integer representing
+// the proper count to skip past the CCTZ fork namespace names.  (This number
+// is one larger when there is an inline namespace name to skip.)
+#if defined(_MSC_VER)
+#if ABSL_OPTION_USE_INLINE_NAMESPACE == 0
+#define ABSL_INTERNAL_MANGLED_NS "absl"
+#define ABSL_INTERNAL_MANGLED_BACKREFERENCE "5"
+#else
+#define ABSL_INTERNAL_MANGLED_NS \
+  ABSL_INTERNAL_TOKEN_STR(ABSL_OPTION_INLINE_NAMESPACE_NAME) "@absl"
+#define ABSL_INTERNAL_MANGLED_BACKREFERENCE "6"
+#endif
+#endif
+
+// ABSL_DLL
+//
+// When building Abseil as a DLL, this macro expands to `__declspec(dllexport)`
+// so we can annotate symbols appropriately as being exported. When used in
+// headers consuming a DLL, this macro expands to `__declspec(dllimport)` so
+// that consumers know the symbol is defined inside the DLL. In all other cases,
+// the macro expands to nothing.
+#if defined(_MSC_VER)
+#if defined(ABSL_BUILD_DLL)
+#define ABSL_DLL __declspec(dllexport)
+#elif defined(ABSL_CONSUME_DLL)
+#define ABSL_DLL __declspec(dllimport)
+#else
+#define ABSL_DLL
+#endif
+#else
+#define ABSL_DLL
+#endif  // defined(_MSC_VER)
+
+// ABSL_HAVE_MEMORY_SANITIZER
+//
+// MemorySanitizer (MSan) is a detector of uninitialized reads. It consists of
+// a compiler instrumentation module and a run-time library.
+#ifdef ABSL_HAVE_MEMORY_SANITIZER
+#error "ABSL_HAVE_MEMORY_SANITIZER cannot be directly set."
+#elif !defined(__native_client__) && ABSL_HAVE_FEATURE(memory_sanitizer)
+#define ABSL_HAVE_MEMORY_SANITIZER 1
+#endif
+
+// ABSL_HAVE_THREAD_SANITIZER
+//
+// ThreadSanitizer (TSan) is a fast data race detector.
+#ifdef ABSL_HAVE_THREAD_SANITIZER
+#error "ABSL_HAVE_THREAD_SANITIZER cannot be directly set."
+#elif defined(__SANITIZE_THREAD__)
+#define ABSL_HAVE_THREAD_SANITIZER 1
+#elif ABSL_HAVE_FEATURE(thread_sanitizer)
+#define ABSL_HAVE_THREAD_SANITIZER 1
+#endif
+
+// ABSL_HAVE_ADDRESS_SANITIZER
+//
+// AddressSanitizer (ASan) is a fast memory error detector.
+#ifdef ABSL_HAVE_ADDRESS_SANITIZER
+#error "ABSL_HAVE_ADDRESS_SANITIZER cannot be directly set."
+#elif defined(__SANITIZE_ADDRESS__)
+#define ABSL_HAVE_ADDRESS_SANITIZER 1
+#elif ABSL_HAVE_FEATURE(address_sanitizer)
+#define ABSL_HAVE_ADDRESS_SANITIZER 1
+#endif
+
+// ABSL_HAVE_HWADDRESS_SANITIZER
+//
+// Hardware-Assisted AddressSanitizer (or HWASAN) is even faster than asan
+// memory error detector which can use CPU features like ARM TBI, Intel LAM or
+// AMD UAI.
+#ifdef ABSL_HAVE_HWADDRESS_SANITIZER
+#error "ABSL_HAVE_HWADDRESS_SANITIZER cannot be directly set."
+#elif defined(__SANITIZE_HWADDRESS__)
+#define ABSL_HAVE_HWADDRESS_SANITIZER 1
+#elif ABSL_HAVE_FEATURE(hwaddress_sanitizer)
+#define ABSL_HAVE_HWADDRESS_SANITIZER 1
+#endif
+
+// ABSL_HAVE_LEAK_SANITIZER
+//
+// LeakSanitizer (or lsan) is a detector of memory leaks.
+// https://clang.llvm.org/docs/LeakSanitizer.html
+// https://github.com/google/sanitizers/wiki/AddressSanitizerLeakSanitizer
+//
+// The macro ABSL_HAVE_LEAK_SANITIZER can be used to detect at compile-time
+// whether the LeakSanitizer is potentially available. However, just because the
+// LeakSanitizer is available does not mean it is active. Use the
+// always-available run-time interface in //absl/debugging/leak_check.h for
+// interacting with LeakSanitizer.
+#ifdef ABSL_HAVE_LEAK_SANITIZER
+#error "ABSL_HAVE_LEAK_SANITIZER cannot be directly set."
+#elif defined(LEAK_SANITIZER)
+// GCC provides no method for detecting the presense of the standalone
+// LeakSanitizer (-fsanitize=leak), so GCC users of -fsanitize=leak should also
+// use -DLEAK_SANITIZER.
+#define ABSL_HAVE_LEAK_SANITIZER 1
+// Clang standalone LeakSanitizer (-fsanitize=leak)
+#elif ABSL_HAVE_FEATURE(leak_sanitizer)
+#define ABSL_HAVE_LEAK_SANITIZER 1
+#elif defined(ABSL_HAVE_ADDRESS_SANITIZER)
+// GCC or Clang using the LeakSanitizer integrated into AddressSanitizer.
+#define ABSL_HAVE_LEAK_SANITIZER 1
+#endif
+
+// ABSL_HAVE_CLASS_TEMPLATE_ARGUMENT_DEDUCTION
+//
+// Class template argument deduction is a language feature added in C++17.
+#ifdef ABSL_HAVE_CLASS_TEMPLATE_ARGUMENT_DEDUCTION
+#error "ABSL_HAVE_CLASS_TEMPLATE_ARGUMENT_DEDUCTION cannot be directly set."
+#elif defined(__cpp_deduction_guides)
+#define ABSL_HAVE_CLASS_TEMPLATE_ARGUMENT_DEDUCTION 1
+#endif
+
+// ABSL_INTERNAL_NEED_REDUNDANT_CONSTEXPR_DECL
+//
+// Prior to C++17, static constexpr variables defined in classes required a
+// separate definition outside of the class body, for example:
+//
+// class Foo {
+//   static constexpr int kBar = 0;
+// };
+// constexpr int Foo::kBar;
+//
+// In C++17, these variables defined in classes are considered inline variables,
+// and the extra declaration is redundant. Since some compilers warn on the
+// extra declarations, ABSL_INTERNAL_NEED_REDUNDANT_CONSTEXPR_DECL can be used
+// conditionally ignore them:
+//
+// #ifdef ABSL_INTERNAL_NEED_REDUNDANT_CONSTEXPR_DECL
+// constexpr int Foo::kBar;
+// #endif
+#if defined(ABSL_INTERNAL_CPLUSPLUS_LANG) && \
+    ABSL_INTERNAL_CPLUSPLUS_LANG < 201703L
+#define ABSL_INTERNAL_NEED_REDUNDANT_CONSTEXPR_DECL 1
+#endif
+
+// `ABSL_INTERNAL_HAS_RTTI` determines whether abseil is being compiled with
+// RTTI support.
+#ifdef ABSL_INTERNAL_HAS_RTTI
+#error ABSL_INTERNAL_HAS_RTTI cannot be directly set
+#elif !defined(__GNUC__) || defined(__GXX_RTTI)
+#define ABSL_INTERNAL_HAS_RTTI 1
+#endif  // !defined(__GNUC__) || defined(__GXX_RTTI)
+
+// ABSL_INTERNAL_HAVE_SSE is used for compile-time detection of SSE support.
+// See https://gcc.gnu.org/onlinedocs/gcc/x86-Options.html for an overview of
+// which architectures support the various x86 instruction sets.
+#ifdef ABSL_INTERNAL_HAVE_SSE
+#error ABSL_INTERNAL_HAVE_SSE cannot be directly set
+#elif defined(__SSE__)
+#define ABSL_INTERNAL_HAVE_SSE 1
+#elif defined(_M_X64) || (defined(_M_IX86_FP) && _M_IX86_FP >= 1)
+// MSVC only defines _M_IX86_FP for x86 32-bit code, and _M_IX86_FP >= 1
+// indicates that at least SSE was targeted with the /arch:SSE option.
+// All x86-64 processors support SSE, so support can be assumed.
+// https://docs.microsoft.com/en-us/cpp/preprocessor/predefined-macros
+#define ABSL_INTERNAL_HAVE_SSE 1
+#endif
+
+// ABSL_INTERNAL_HAVE_SSE2 is used for compile-time detection of SSE2 support.
+// See https://gcc.gnu.org/onlinedocs/gcc/x86-Options.html for an overview of
+// which architectures support the various x86 instruction sets.
+#ifdef ABSL_INTERNAL_HAVE_SSE2
+#error ABSL_INTERNAL_HAVE_SSE2 cannot be directly set
+#elif defined(__SSE2__)
+#define ABSL_INTERNAL_HAVE_SSE2 1
+#elif defined(_M_X64) || (defined(_M_IX86_FP) && _M_IX86_FP >= 2)
+// MSVC only defines _M_IX86_FP for x86 32-bit code, and _M_IX86_FP >= 2
+// indicates that at least SSE2 was targeted with the /arch:SSE2 option.
+// All x86-64 processors support SSE2, so support can be assumed.
+// https://docs.microsoft.com/en-us/cpp/preprocessor/predefined-macros
+#define ABSL_INTERNAL_HAVE_SSE2 1
+#endif
+
+// ABSL_INTERNAL_HAVE_SSSE3 is used for compile-time detection of SSSE3 support.
+// See https://gcc.gnu.org/onlinedocs/gcc/x86-Options.html for an overview of
+// which architectures support the various x86 instruction sets.
+//
+// MSVC does not have a mode that targets SSSE3 at compile-time. To use SSSE3
+// with MSVC requires either assuming that the code will only every run on CPUs
+// that support SSSE3, otherwise __cpuid() can be used to detect support at
+// runtime and fallback to a non-SSSE3 implementation when SSSE3 is unsupported
+// by the CPU.
+#ifdef ABSL_INTERNAL_HAVE_SSSE3
+#error ABSL_INTERNAL_HAVE_SSSE3 cannot be directly set
+#elif defined(__SSSE3__)
+#define ABSL_INTERNAL_HAVE_SSSE3 1
+#endif
+
+// ABSL_INTERNAL_HAVE_ARM_NEON is used for compile-time detection of NEON (ARM
+// SIMD).
+#ifdef ABSL_INTERNAL_HAVE_ARM_NEON
+#error ABSL_INTERNAL_HAVE_ARM_NEON cannot be directly set
+#elif defined(__ARM_NEON)
+#define ABSL_INTERNAL_HAVE_ARM_NEON 1
+#endif
+
+#endif  // ABSL_BASE_CONFIG_H_
--- a/include/absl/base/const_init.h
+++ b/include/absl/base/const_init.h
@ -0,0 +1,76 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// -----------------------------------------------------------------------------
+// kConstInit
+// -----------------------------------------------------------------------------
+//
+// A constructor tag used to mark an object as safe for use as a global
+// variable, avoiding the usual lifetime issues that can affect globals.
+
+#ifndef ABSL_BASE_CONST_INIT_H_
+#define ABSL_BASE_CONST_INIT_H_
+
+#include "absl/base/config.h"
+
+// In general, objects with static storage duration (such as global variables)
+// can trigger tricky object lifetime situations.  Attempting to access them
+// from the constructors or destructors of other global objects can result in
+// undefined behavior, unless their constructors and destructors are designed
+// with this issue in mind.
+//
+// The normal way to deal with this issue in C++11 is to use constant
+// initialization and trivial destructors.
+//
+// Constant initialization is guaranteed to occur before any other code
+// executes.  Constructors that are declared 'constexpr' are eligible for
+// constant initialization.  You can annotate a variable declaration with the
+// ABSL_CONST_INIT macro to express this intent.  For compilers that support
+// it, this annotation will cause a compilation error for declarations that
+// aren't subject to constant initialization (perhaps because a runtime value
+// was passed as a constructor argument).
+//
+// On program shutdown, lifetime issues can be avoided on global objects by
+// ensuring that they contain  trivial destructors.  A class has a trivial
+// destructor unless it has a user-defined destructor, a virtual method or base
+// class, or a data member or base class with a non-trivial destructor of its
+// own.  Objects with static storage duration and a trivial destructor are not
+// cleaned up on program shutdown, and are thus safe to access from other code
+// running during shutdown.
+//
+// For a few core Abseil classes, we make a best effort to allow for safe global
+// instances, even though these classes have non-trivial destructors.  These
+// objects can be created with the absl::kConstInit tag.  For example:
+//   ABSL_CONST_INIT absl::Mutex global_mutex(absl::kConstInit);
+//
+// The line above declares a global variable of type absl::Mutex which can be
+// accessed at any point during startup or shutdown.  global_mutex's destructor
+// will still run, but will not invalidate the object.  Note that C++ specifies
+// that accessing an object after its destructor has run results in undefined
+// behavior, but this pattern works on the toolchains we support.
+//
+// The absl::kConstInit tag should only be used to define objects with static
+// or thread_local storage duration.
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+
+enum ConstInitType {
+  kConstInit,
+};
+
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_BASE_CONST_INIT_H_
--- a/include/absl/base/dynamic_annotations.h
+++ b/include/absl/base/dynamic_annotations.h
@ -0,0 +1,471 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// This file defines dynamic annotations for use with dynamic analysis tool
+// such as valgrind, PIN, etc.
+//
+// Dynamic annotation is a source code annotation that affects the generated
+// code (that is, the annotation is not a comment). Each such annotation is
+// attached to a particular instruction and/or to a particular object (address)
+// in the program.
+//
+// The annotations that should be used by users are macros in all upper-case
+// (e.g., ABSL_ANNOTATE_THREAD_NAME).
+//
+// Actual implementation of these macros may differ depending on the dynamic
+// analysis tool being used.
+//
+// This file supports the following configurations:
+// - Dynamic Annotations enabled (with static thread-safety warnings disabled).
+//   In this case, macros expand to functions implemented by Thread Sanitizer,
+//   when building with TSan. When not provided an external implementation,
+//   dynamic_annotations.cc provides no-op implementations.
+//
+// - Static Clang thread-safety warnings enabled.
+//   When building with a Clang compiler that supports thread-safety warnings,
+//   a subset of annotations can be statically-checked at compile-time. We
+//   expand these macros to static-inline functions that can be analyzed for
+//   thread-safety, but afterwards elided when building the final binary.
+//
+// - All annotations are disabled.
+//   If neither Dynamic Annotations nor Clang thread-safety warnings are
+//   enabled, then all annotation-macros expand to empty.
+
+#ifndef ABSL_BASE_DYNAMIC_ANNOTATIONS_H_
+#define ABSL_BASE_DYNAMIC_ANNOTATIONS_H_
+
+#include <stddef.h>
+
+#include "absl/base/attributes.h"
+#include "absl/base/config.h"
+#ifdef __cplusplus
+#include "absl/base/macros.h"
+#endif
+
+// TODO(rogeeff): Remove after the backward compatibility period.
+#include "absl/base/internal/dynamic_annotations.h"  // IWYU pragma: export
+
+// -------------------------------------------------------------------------
+// Decide which features are enabled.
+
+#ifdef ABSL_HAVE_THREAD_SANITIZER
+
+#define ABSL_INTERNAL_RACE_ANNOTATIONS_ENABLED 1
+#define ABSL_INTERNAL_READS_ANNOTATIONS_ENABLED 1
+#define ABSL_INTERNAL_WRITES_ANNOTATIONS_ENABLED 1
+#define ABSL_INTERNAL_ANNOTALYSIS_ENABLED 0
+#define ABSL_INTERNAL_READS_WRITES_ANNOTATIONS_ENABLED 1
+
+#else
+
+#define ABSL_INTERNAL_RACE_ANNOTATIONS_ENABLED 0
+#define ABSL_INTERNAL_READS_ANNOTATIONS_ENABLED 0
+#define ABSL_INTERNAL_WRITES_ANNOTATIONS_ENABLED 0
+
+// Clang provides limited support for static thread-safety analysis through a
+// feature called Annotalysis. We configure macro-definitions according to
+// whether Annotalysis support is available. When running in opt-mode, GCC
+// will issue a warning, if these attributes are compiled. Only include them
+// when compiling using Clang.
+
+#if defined(__clang__)
+#define ABSL_INTERNAL_ANNOTALYSIS_ENABLED 1
+#if !defined(SWIG)
+#define ABSL_INTERNAL_IGNORE_READS_ATTRIBUTE_ENABLED 1
+#endif
+#else
+#define ABSL_INTERNAL_ANNOTALYSIS_ENABLED 0
+#endif
+
+// Read/write annotations are enabled in Annotalysis mode; disabled otherwise.
+#define ABSL_INTERNAL_READS_WRITES_ANNOTATIONS_ENABLED \
+  ABSL_INTERNAL_ANNOTALYSIS_ENABLED
+
+#endif  // ABSL_HAVE_THREAD_SANITIZER
+
+#ifdef __cplusplus
+#define ABSL_INTERNAL_BEGIN_EXTERN_C extern "C" {
+#define ABSL_INTERNAL_END_EXTERN_C }  // extern "C"
+#define ABSL_INTERNAL_GLOBAL_SCOPED(F) ::F
+#define ABSL_INTERNAL_STATIC_INLINE inline
+#else
+#define ABSL_INTERNAL_BEGIN_EXTERN_C  // empty
+#define ABSL_INTERNAL_END_EXTERN_C    // empty
+#define ABSL_INTERNAL_GLOBAL_SCOPED(F) F
+#define ABSL_INTERNAL_STATIC_INLINE static inline
+#endif
+
+// -------------------------------------------------------------------------
+// Define race annotations.
+
+#if ABSL_INTERNAL_RACE_ANNOTATIONS_ENABLED == 1
+// Some of the symbols used in this section (e.g. AnnotateBenignRaceSized) are
+// defined by the compiler-based santizer implementation, not by the Abseil
+// library. Therefore they do not use ABSL_INTERNAL_C_SYMBOL.
+
+// -------------------------------------------------------------
+// Annotations that suppress errors. It is usually better to express the
+// program's synchronization using the other annotations, but these can be used
+// when all else fails.
+
+// Report that we may have a benign race at `pointer`, with size
+// "sizeof(*(pointer))". `pointer` must be a non-void* pointer. Insert at the
+// point where `pointer` has been allocated, preferably close to the point
+// where the race happens. See also ABSL_ANNOTATE_BENIGN_RACE_STATIC.
+#define ABSL_ANNOTATE_BENIGN_RACE(pointer, description) \
+  ABSL_INTERNAL_GLOBAL_SCOPED(AnnotateBenignRaceSized)  \
+  (__FILE__, __LINE__, pointer, sizeof(*(pointer)), description)
+
+// Same as ABSL_ANNOTATE_BENIGN_RACE(`address`, `description`), but applies to
+// the memory range [`address`, `address`+`size`).
+#define ABSL_ANNOTATE_BENIGN_RACE_SIZED(address, size, description) \
+  ABSL_INTERNAL_GLOBAL_SCOPED(AnnotateBenignRaceSized)              \
+  (__FILE__, __LINE__, address, size, description)
+
+// Enable (`enable`!=0) or disable (`enable`==0) race detection for all threads.
+// This annotation could be useful if you want to skip expensive race analysis
+// during some period of program execution, e.g. during initialization.
+#define ABSL_ANNOTATE_ENABLE_RACE_DETECTION(enable)        \
+  ABSL_INTERNAL_GLOBAL_SCOPED(AnnotateEnableRaceDetection) \
+  (__FILE__, __LINE__, enable)
+
+// -------------------------------------------------------------
+// Annotations useful for debugging.
+
+// Report the current thread `name` to a race detector.
+#define ABSL_ANNOTATE_THREAD_NAME(name) \
+  ABSL_INTERNAL_GLOBAL_SCOPED(AnnotateThreadName)(__FILE__, __LINE__, name)
+
+// -------------------------------------------------------------
+// Annotations useful when implementing locks. They are not normally needed by
+// modules that merely use locks. The `lock` argument is a pointer to the lock
+// object.
+
+// Report that a lock has been created at address `lock`.
+#define ABSL_ANNOTATE_RWLOCK_CREATE(lock) \
+  ABSL_INTERNAL_GLOBAL_SCOPED(AnnotateRWLockCreate)(__FILE__, __LINE__, lock)
+
+// Report that a linker initialized lock has been created at address `lock`.
+#ifdef ABSL_HAVE_THREAD_SANITIZER
+#define ABSL_ANNOTATE_RWLOCK_CREATE_STATIC(lock)          \
+  ABSL_INTERNAL_GLOBAL_SCOPED(AnnotateRWLockCreateStatic) \
+  (__FILE__, __LINE__, lock)
+#else
+#define ABSL_ANNOTATE_RWLOCK_CREATE_STATIC(lock) \
+  ABSL_ANNOTATE_RWLOCK_CREATE(lock)
+#endif
+
+// Report that the lock at address `lock` is about to be destroyed.
+#define ABSL_ANNOTATE_RWLOCK_DESTROY(lock) \
+  ABSL_INTERNAL_GLOBAL_SCOPED(AnnotateRWLockDestroy)(__FILE__, __LINE__, lock)
+
+// Report that the lock at address `lock` has been acquired.
+// `is_w`=1 for writer lock, `is_w`=0 for reader lock.
+#define ABSL_ANNOTATE_RWLOCK_ACQUIRED(lock, is_w)     \
+  ABSL_INTERNAL_GLOBAL_SCOPED(AnnotateRWLockAcquired) \
+  (__FILE__, __LINE__, lock, is_w)
+
+// Report that the lock at address `lock` is about to be released.
+// `is_w`=1 for writer lock, `is_w`=0 for reader lock.
+#define ABSL_ANNOTATE_RWLOCK_RELEASED(lock, is_w)     \
+  ABSL_INTERNAL_GLOBAL_SCOPED(AnnotateRWLockReleased) \
+  (__FILE__, __LINE__, lock, is_w)
+
+// Apply ABSL_ANNOTATE_BENIGN_RACE_SIZED to a static variable `static_var`.
+#define ABSL_ANNOTATE_BENIGN_RACE_STATIC(static_var, description)      \
+  namespace {                                                          \
+  class static_var##_annotator {                                       \
+   public:                                                             \
+    static_var##_annotator() {                                         \
+      ABSL_ANNOTATE_BENIGN_RACE_SIZED(&static_var, sizeof(static_var), \
+                                      #static_var ": " description);   \
+    }                                                                  \
+  };                                                                   \
+  static static_var##_annotator the##static_var##_annotator;           \
+  }  // namespace
+
+// Function prototypes of annotations provided by the compiler-based sanitizer
+// implementation.
+ABSL_INTERNAL_BEGIN_EXTERN_C
+void AnnotateRWLockCreate(const char* file, int line,
+                          const volatile void* lock);
+void AnnotateRWLockCreateStatic(const char* file, int line,
+                                const volatile void* lock);
+void AnnotateRWLockDestroy(const char* file, int line,
+                           const volatile void* lock);
+void AnnotateRWLockAcquired(const char* file, int line,
+                            const volatile void* lock, long is_w);  // NOLINT
+void AnnotateRWLockReleased(const char* file, int line,
+                            const volatile void* lock, long is_w);  // NOLINT
+void AnnotateBenignRace(const char* file, int line,
+                        const volatile void* address, const char* description);
+void AnnotateBenignRaceSized(const char* file, int line,
+                             const volatile void* address, size_t size,
+                             const char* description);
+void AnnotateThreadName(const char* file, int line, const char* name);
+void AnnotateEnableRaceDetection(const char* file, int line, int enable);
+ABSL_INTERNAL_END_EXTERN_C
+
+#else  // ABSL_INTERNAL_RACE_ANNOTATIONS_ENABLED == 0
+
+#define ABSL_ANNOTATE_RWLOCK_CREATE(lock)                            // empty
+#define ABSL_ANNOTATE_RWLOCK_CREATE_STATIC(lock)                     // empty
+#define ABSL_ANNOTATE_RWLOCK_DESTROY(lock)                           // empty
+#define ABSL_ANNOTATE_RWLOCK_ACQUIRED(lock, is_w)                    // empty
+#define ABSL_ANNOTATE_RWLOCK_RELEASED(lock, is_w)                    // empty
+#define ABSL_ANNOTATE_BENIGN_RACE(address, description)              // empty
+#define ABSL_ANNOTATE_BENIGN_RACE_SIZED(address, size, description)  // empty
+#define ABSL_ANNOTATE_THREAD_NAME(name)                              // empty
+#define ABSL_ANNOTATE_ENABLE_RACE_DETECTION(enable)                  // empty
+#define ABSL_ANNOTATE_BENIGN_RACE_STATIC(static_var, description)    // empty
+
+#endif  // ABSL_INTERNAL_RACE_ANNOTATIONS_ENABLED
+
+// -------------------------------------------------------------------------
+// Define memory annotations.
+
+#ifdef ABSL_HAVE_MEMORY_SANITIZER
+
+#include <sanitizer/msan_interface.h>
+
+#define ABSL_ANNOTATE_MEMORY_IS_INITIALIZED(address, size) \
+  __msan_unpoison(address, size)
+
+#define ABSL_ANNOTATE_MEMORY_IS_UNINITIALIZED(address, size) \
+  __msan_allocated_memory(address, size)
+
+#else  // !defined(ABSL_HAVE_MEMORY_SANITIZER)
+
+// TODO(rogeeff): remove this branch
+#ifdef ABSL_HAVE_THREAD_SANITIZER
+#define ABSL_ANNOTATE_MEMORY_IS_INITIALIZED(address, size) \
+  do {                                                     \
+    (void)(address);                                       \
+    (void)(size);                                          \
+  } while (0)
+#define ABSL_ANNOTATE_MEMORY_IS_UNINITIALIZED(address, size) \
+  do {                                                       \
+    (void)(address);                                         \
+    (void)(size);                                            \
+  } while (0)
+#else
+
+#define ABSL_ANNOTATE_MEMORY_IS_INITIALIZED(address, size)    // empty
+#define ABSL_ANNOTATE_MEMORY_IS_UNINITIALIZED(address, size)  // empty
+
+#endif
+
+#endif  // ABSL_HAVE_MEMORY_SANITIZER
+
+// -------------------------------------------------------------------------
+// Define IGNORE_READS_BEGIN/_END attributes.
+
+#if defined(ABSL_INTERNAL_IGNORE_READS_ATTRIBUTE_ENABLED)
+
+#define ABSL_INTERNAL_IGNORE_READS_BEGIN_ATTRIBUTE \
+  __attribute((exclusive_lock_function("*")))
+#define ABSL_INTERNAL_IGNORE_READS_END_ATTRIBUTE \
+  __attribute((unlock_function("*")))
+
+#else  // !defined(ABSL_INTERNAL_IGNORE_READS_ATTRIBUTE_ENABLED)
+
+#define ABSL_INTERNAL_IGNORE_READS_BEGIN_ATTRIBUTE  // empty
+#define ABSL_INTERNAL_IGNORE_READS_END_ATTRIBUTE    // empty
+
+#endif  // defined(ABSL_INTERNAL_IGNORE_READS_ATTRIBUTE_ENABLED)
+
+// -------------------------------------------------------------------------
+// Define IGNORE_READS_BEGIN/_END annotations.
+
+#if ABSL_INTERNAL_READS_ANNOTATIONS_ENABLED == 1
+// Some of the symbols used in this section (e.g. AnnotateIgnoreReadsBegin) are
+// defined by the compiler-based implementation, not by the Abseil
+// library. Therefore they do not use ABSL_INTERNAL_C_SYMBOL.
+
+// Request the analysis tool to ignore all reads in the current thread until
+// ABSL_ANNOTATE_IGNORE_READS_END is called. Useful to ignore intentional racey
+// reads, while still checking other reads and all writes.
+// See also ABSL_ANNOTATE_UNPROTECTED_READ.
+#define ABSL_ANNOTATE_IGNORE_READS_BEGIN()              \
+  ABSL_INTERNAL_GLOBAL_SCOPED(AnnotateIgnoreReadsBegin) \
+  (__FILE__, __LINE__)
+
+// Stop ignoring reads.
+#define ABSL_ANNOTATE_IGNORE_READS_END()              \
+  ABSL_INTERNAL_GLOBAL_SCOPED(AnnotateIgnoreReadsEnd) \
+  (__FILE__, __LINE__)
+
+// Function prototypes of annotations provided by the compiler-based sanitizer
+// implementation.
+ABSL_INTERNAL_BEGIN_EXTERN_C
+void AnnotateIgnoreReadsBegin(const char* file, int line)
+    ABSL_INTERNAL_IGNORE_READS_BEGIN_ATTRIBUTE;
+void AnnotateIgnoreReadsEnd(const char* file,
+                            int line) ABSL_INTERNAL_IGNORE_READS_END_ATTRIBUTE;
+ABSL_INTERNAL_END_EXTERN_C
+
+#elif defined(ABSL_INTERNAL_ANNOTALYSIS_ENABLED)
+
+// When Annotalysis is enabled without Dynamic Annotations, the use of
+// static-inline functions allows the annotations to be read at compile-time,
+// while still letting the compiler elide the functions from the final build.
+//
+// TODO(delesley) -- The exclusive lock here ignores writes as well, but
+// allows IGNORE_READS_AND_WRITES to work properly.
+
+#define ABSL_ANNOTATE_IGNORE_READS_BEGIN()                          \
+  ABSL_INTERNAL_GLOBAL_SCOPED(                                      \
+      ABSL_INTERNAL_C_SYMBOL(AbslInternalAnnotateIgnoreReadsBegin)) \
+  ()
+
+#define ABSL_ANNOTATE_IGNORE_READS_END()                          \
+  ABSL_INTERNAL_GLOBAL_SCOPED(                                    \
+      ABSL_INTERNAL_C_SYMBOL(AbslInternalAnnotateIgnoreReadsEnd)) \
+  ()
+
+ABSL_INTERNAL_STATIC_INLINE void ABSL_INTERNAL_C_SYMBOL(
+    AbslInternalAnnotateIgnoreReadsBegin)()
+    ABSL_INTERNAL_IGNORE_READS_BEGIN_ATTRIBUTE {}
+
+ABSL_INTERNAL_STATIC_INLINE void ABSL_INTERNAL_C_SYMBOL(
+    AbslInternalAnnotateIgnoreReadsEnd)()
+    ABSL_INTERNAL_IGNORE_READS_END_ATTRIBUTE {}
+
+#else
+
+#define ABSL_ANNOTATE_IGNORE_READS_BEGIN()  // empty
+#define ABSL_ANNOTATE_IGNORE_READS_END()    // empty
+
+#endif
+
+// -------------------------------------------------------------------------
+// Define IGNORE_WRITES_BEGIN/_END annotations.
+
+#if ABSL_INTERNAL_WRITES_ANNOTATIONS_ENABLED == 1
+
+// Similar to ABSL_ANNOTATE_IGNORE_READS_BEGIN, but ignore writes instead.
+#define ABSL_ANNOTATE_IGNORE_WRITES_BEGIN() \
+  ABSL_INTERNAL_GLOBAL_SCOPED(AnnotateIgnoreWritesBegin)(__FILE__, __LINE__)
+
+// Stop ignoring writes.
+#define ABSL_ANNOTATE_IGNORE_WRITES_END() \
+  ABSL_INTERNAL_GLOBAL_SCOPED(AnnotateIgnoreWritesEnd)(__FILE__, __LINE__)
+
+// Function prototypes of annotations provided by the compiler-based sanitizer
+// implementation.
+ABSL_INTERNAL_BEGIN_EXTERN_C
+void AnnotateIgnoreWritesBegin(const char* file, int line);
+void AnnotateIgnoreWritesEnd(const char* file, int line);
+ABSL_INTERNAL_END_EXTERN_C
+
+#else
+
+#define ABSL_ANNOTATE_IGNORE_WRITES_BEGIN()  // empty
+#define ABSL_ANNOTATE_IGNORE_WRITES_END()    // empty
+
+#endif
+
+// -------------------------------------------------------------------------
+// Define the ABSL_ANNOTATE_IGNORE_READS_AND_WRITES_* annotations using the more
+// primitive annotations defined above.
+//
+//     Instead of doing
+//        ABSL_ANNOTATE_IGNORE_READS_BEGIN();
+//        ... = x;
+//        ABSL_ANNOTATE_IGNORE_READS_END();
+//     one can use
+//        ... = ABSL_ANNOTATE_UNPROTECTED_READ(x);
+
+#if defined(ABSL_INTERNAL_READS_WRITES_ANNOTATIONS_ENABLED)
+
+// Start ignoring all memory accesses (both reads and writes).
+#define ABSL_ANNOTATE_IGNORE_READS_AND_WRITES_BEGIN() \
+  do {                                                \
+    ABSL_ANNOTATE_IGNORE_READS_BEGIN();               \
+    ABSL_ANNOTATE_IGNORE_WRITES_BEGIN();              \
+  } while (0)
+
+// Stop ignoring both reads and writes.
+#define ABSL_ANNOTATE_IGNORE_READS_AND_WRITES_END() \
+  do {                                              \
+    ABSL_ANNOTATE_IGNORE_WRITES_END();              \
+    ABSL_ANNOTATE_IGNORE_READS_END();               \
+  } while (0)
+
+#ifdef __cplusplus
+// ABSL_ANNOTATE_UNPROTECTED_READ is the preferred way to annotate racey reads.
+#define ABSL_ANNOTATE_UNPROTECTED_READ(x) \
+  absl::base_internal::AnnotateUnprotectedRead(x)
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace base_internal {
+
+template <typename T>
+inline T AnnotateUnprotectedRead(const volatile T& x) {  // NOLINT
+  ABSL_ANNOTATE_IGNORE_READS_BEGIN();
+  T res = x;
+  ABSL_ANNOTATE_IGNORE_READS_END();
+  return res;
+}
+
+}  // namespace base_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+#endif
+
+#else
+
+#define ABSL_ANNOTATE_IGNORE_READS_AND_WRITES_BEGIN()  // empty
+#define ABSL_ANNOTATE_IGNORE_READS_AND_WRITES_END()    // empty
+#define ABSL_ANNOTATE_UNPROTECTED_READ(x) (x)
+
+#endif
+
+// -------------------------------------------------------------------------
+// Address sanitizer annotations
+
+#ifdef ABSL_HAVE_ADDRESS_SANITIZER
+// Describe the current state of a contiguous container such as e.g.
+// std::vector or std::string. For more details see
+// sanitizer/common_interface_defs.h, which is provided by the compiler.
+#include <sanitizer/common_interface_defs.h>
+
+#define ABSL_ANNOTATE_CONTIGUOUS_CONTAINER(beg, end, old_mid, new_mid) \
+  __sanitizer_annotate_contiguous_container(beg, end, old_mid, new_mid)
+#define ABSL_ADDRESS_SANITIZER_REDZONE(name) \
+  struct {                                   \
+    alignas(8) char x[8];                    \
+  } name
+
+#else
+
+#define ABSL_ANNOTATE_CONTIGUOUS_CONTAINER(beg, end, old_mid, new_mid)  // empty
+#define ABSL_ADDRESS_SANITIZER_REDZONE(name) static_assert(true, "")
+
+#endif  // ABSL_HAVE_ADDRESS_SANITIZER
+
+// -------------------------------------------------------------------------
+// Undefine the macros intended only for this file.
+
+#undef ABSL_INTERNAL_RACE_ANNOTATIONS_ENABLED
+#undef ABSL_INTERNAL_READS_ANNOTATIONS_ENABLED
+#undef ABSL_INTERNAL_WRITES_ANNOTATIONS_ENABLED
+#undef ABSL_INTERNAL_ANNOTALYSIS_ENABLED
+#undef ABSL_INTERNAL_READS_WRITES_ANNOTATIONS_ENABLED
+#undef ABSL_INTERNAL_BEGIN_EXTERN_C
+#undef ABSL_INTERNAL_END_EXTERN_C
+#undef ABSL_INTERNAL_STATIC_INLINE
+
+#endif  // ABSL_BASE_DYNAMIC_ANNOTATIONS_H_
--- a/include/absl/base/internal/atomic_hook.h
+++ b/include/absl/base/internal/atomic_hook.h
@ -0,0 +1,200 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef ABSL_BASE_INTERNAL_ATOMIC_HOOK_H_
+#define ABSL_BASE_INTERNAL_ATOMIC_HOOK_H_
+
+#include <atomic>
+#include <cassert>
+#include <cstdint>
+#include <utility>
+
+#include "absl/base/attributes.h"
+#include "absl/base/config.h"
+
+#if defined(_MSC_VER) && !defined(__clang__)
+#define ABSL_HAVE_WORKING_CONSTEXPR_STATIC_INIT 0
+#else
+#define ABSL_HAVE_WORKING_CONSTEXPR_STATIC_INIT 1
+#endif
+
+#if defined(_MSC_VER)
+#define ABSL_HAVE_WORKING_ATOMIC_POINTER 0
+#else
+#define ABSL_HAVE_WORKING_ATOMIC_POINTER 1
+#endif
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace base_internal {
+
+template <typename T>
+class AtomicHook;
+
+// To workaround AtomicHook not being constant-initializable on some platforms,
+// prefer to annotate instances with `ABSL_INTERNAL_ATOMIC_HOOK_ATTRIBUTES`
+// instead of `ABSL_CONST_INIT`.
+#if ABSL_HAVE_WORKING_CONSTEXPR_STATIC_INIT
+#define ABSL_INTERNAL_ATOMIC_HOOK_ATTRIBUTES ABSL_CONST_INIT
+#else
+#define ABSL_INTERNAL_ATOMIC_HOOK_ATTRIBUTES
+#endif
+
+// `AtomicHook` is a helper class, templatized on a raw function pointer type,
+// for implementing Abseil customization hooks.  It is a callable object that
+// dispatches to the registered hook.  Objects of type `AtomicHook` must have
+// static or thread storage duration.
+//
+// A default constructed object performs a no-op (and returns a default
+// constructed object) if no hook has been registered.
+//
+// Hooks can be pre-registered via constant initialization, for example:
+//
+// ABSL_INTERNAL_ATOMIC_HOOK_ATTRIBUTES static AtomicHook<void(*)()>
+//     my_hook(DefaultAction);
+//
+// and then changed at runtime via a call to `Store()`.
+//
+// Reads and writes guarantee memory_order_acquire/memory_order_release
+// semantics.
+template <typename ReturnType, typename... Args>
+class AtomicHook<ReturnType (*)(Args...)> {
+ public:
+  using FnPtr = ReturnType (*)(Args...);
+
+  // Constructs an object that by default performs a no-op (and
+  // returns a default constructed object) when no hook as been registered.
+  constexpr AtomicHook() : AtomicHook(DummyFunction) {}
+
+  // Constructs an object that by default dispatches to/returns the
+  // pre-registered default_fn when no hook has been registered at runtime.
+#if ABSL_HAVE_WORKING_ATOMIC_POINTER && ABSL_HAVE_WORKING_CONSTEXPR_STATIC_INIT
+  explicit constexpr AtomicHook(FnPtr default_fn)
+      : hook_(default_fn), default_fn_(default_fn) {}
+#elif ABSL_HAVE_WORKING_CONSTEXPR_STATIC_INIT
+  explicit constexpr AtomicHook(FnPtr default_fn)
+      : hook_(kUninitialized), default_fn_(default_fn) {}
+#else
+  // As of January 2020, on all known versions of MSVC this constructor runs in
+  // the global constructor sequence.  If `Store()` is called by a dynamic
+  // initializer, we want to preserve the value, even if this constructor runs
+  // after the call to `Store()`.  If not, `hook_` will be
+  // zero-initialized by the linker and we have no need to set it.
+  // https://developercommunity.visualstudio.com/content/problem/336946/class-with-constexpr-constructor-not-using-static.html
+  explicit constexpr AtomicHook(FnPtr default_fn)
+      : /* hook_(deliberately omitted), */ default_fn_(default_fn) {
+    static_assert(kUninitialized == 0, "here we rely on zero-initialization");
+  }
+#endif
+
+  // Stores the provided function pointer as the value for this hook.
+  //
+  // This is intended to be called once.  Multiple calls are legal only if the
+  // same function pointer is provided for each call.  The store is implemented
+  // as a memory_order_release operation, and read accesses are implemented as
+  // memory_order_acquire.
+  void Store(FnPtr fn) {
+    bool success = DoStore(fn);
+    static_cast<void>(success);
+    assert(success);
+  }
+
+  // Invokes the registered callback.  If no callback has yet been registered, a
+  // default-constructed object of the appropriate type is returned instead.
+  template <typename... CallArgs>
+  ReturnType operator()(CallArgs&&... args) const {
+    return DoLoad()(std::forward<CallArgs>(args)...);
+  }
+
+  // Returns the registered callback, or nullptr if none has been registered.
+  // Useful if client code needs to conditionalize behavior based on whether a
+  // callback was registered.
+  //
+  // Note that atomic_hook.Load()() and atomic_hook() have different semantics:
+  // operator()() will perform a no-op if no callback was registered, while
+  // Load()() will dereference a null function pointer.  Prefer operator()() to
+  // Load()() unless you must conditionalize behavior on whether a hook was
+  // registered.
+  FnPtr Load() const {
+    FnPtr ptr = DoLoad();
+    return (ptr == DummyFunction) ? nullptr : ptr;
+  }
+
+ private:
+  static ReturnType DummyFunction(Args...) {
+    return ReturnType();
+  }
+
+  // Current versions of MSVC (as of September 2017) have a broken
+  // implementation of std::atomic<T*>:  Its constructor attempts to do the
+  // equivalent of a reinterpret_cast in a constexpr context, which is not
+  // allowed.
+  //
+  // This causes an issue when building with LLVM under Windows.  To avoid this,
+  // we use a less-efficient, intptr_t-based implementation on Windows.
+#if ABSL_HAVE_WORKING_ATOMIC_POINTER
+  // Return the stored value, or DummyFunction if no value has been stored.
+  FnPtr DoLoad() const { return hook_.load(std::memory_order_acquire); }
+
+  // Store the given value.  Returns false if a different value was already
+  // stored to this object.
+  bool DoStore(FnPtr fn) {
+    assert(fn);
+    FnPtr expected = default_fn_;
+    const bool store_succeeded = hook_.compare_exchange_strong(
+        expected, fn, std::memory_order_acq_rel, std::memory_order_acquire);
+    const bool same_value_already_stored = (expected == fn);
+    return store_succeeded || same_value_already_stored;
+  }
+
+  std::atomic<FnPtr> hook_;
+#else  // !ABSL_HAVE_WORKING_ATOMIC_POINTER
+  // Use a sentinel value unlikely to be the address of an actual function.
+  static constexpr intptr_t kUninitialized = 0;
+
+  static_assert(sizeof(intptr_t) >= sizeof(FnPtr),
+                "intptr_t can't contain a function pointer");
+
+  FnPtr DoLoad() const {
+    const intptr_t value = hook_.load(std::memory_order_acquire);
+    if (value == kUninitialized) {
+      return default_fn_;
+    }
+    return reinterpret_cast<FnPtr>(value);
+  }
+
+  bool DoStore(FnPtr fn) {
+    assert(fn);
+    const auto value = reinterpret_cast<intptr_t>(fn);
+    intptr_t expected = kUninitialized;
+    const bool store_succeeded = hook_.compare_exchange_strong(
+        expected, value, std::memory_order_acq_rel, std::memory_order_acquire);
+    const bool same_value_already_stored = (expected == value);
+    return store_succeeded || same_value_already_stored;
+  }
+
+  std::atomic<intptr_t> hook_;
+#endif
+
+  const FnPtr default_fn_;
+};
+
+#undef ABSL_HAVE_WORKING_ATOMIC_POINTER
+#undef ABSL_HAVE_WORKING_CONSTEXPR_STATIC_INIT
+
+}  // namespace base_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_BASE_INTERNAL_ATOMIC_HOOK_H_
--- a/include/absl/base/internal/atomic_hook_test_helper.h
+++ b/include/absl/base/internal/atomic_hook_test_helper.h
@ -0,0 +1,34 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef ABSL_BASE_ATOMIC_HOOK_TEST_HELPER_H_
+#define ABSL_BASE_ATOMIC_HOOK_TEST_HELPER_H_
+
+#include "absl/base/internal/atomic_hook.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace atomic_hook_internal {
+
+using VoidF = void (*)();
+extern absl::base_internal::AtomicHook<VoidF> func;
+extern int default_func_calls;
+void DefaultFunc();
+void RegisterFunc(VoidF func);
+
+}  // namespace atomic_hook_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_BASE_ATOMIC_HOOK_TEST_HELPER_H_
--- a/include/absl/base/internal/cycleclock.h
+++ b/include/absl/base/internal/cycleclock.h
@ -0,0 +1,159 @@
+//
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+// -----------------------------------------------------------------------------
+// File: cycleclock.h
+// -----------------------------------------------------------------------------
+//
+// This header file defines a `CycleClock`, which yields the value and frequency
+// of a cycle counter that increments at a rate that is approximately constant.
+//
+// NOTE:
+//
+// The cycle counter frequency is not necessarily related to the core clock
+// frequency and should not be treated as such. That is, `CycleClock` cycles are
+// not necessarily "CPU cycles" and code should not rely on that behavior, even
+// if experimentally observed.
+//
+// An arbitrary offset may have been added to the counter at power on.
+//
+// On some platforms, the rate and offset of the counter may differ
+// slightly when read from different CPUs of a multiprocessor. Usually,
+// we try to ensure that the operating system adjusts values periodically
+// so that values agree approximately.   If you need stronger guarantees,
+// consider using alternate interfaces.
+//
+// The CPU is not required to maintain the ordering of a cycle counter read
+// with respect to surrounding instructions.
+
+#ifndef ABSL_BASE_INTERNAL_CYCLECLOCK_H_
+#define ABSL_BASE_INTERNAL_CYCLECLOCK_H_
+
+#include <atomic>
+#include <cstdint>
+
+#include "absl/base/attributes.h"
+#include "absl/base/config.h"
+#include "absl/base/internal/unscaledcycleclock.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace base_internal {
+
+using CycleClockSourceFunc = int64_t (*)();
+
+// -----------------------------------------------------------------------------
+// CycleClock
+// -----------------------------------------------------------------------------
+class CycleClock {
+ public:
+  // CycleClock::Now()
+  //
+  // Returns the value of a cycle counter that counts at a rate that is
+  // approximately constant.
+  static int64_t Now();
+
+  // CycleClock::Frequency()
+  //
+  // Returns the amount by which `CycleClock::Now()` increases per second. Note
+  // that this value may not necessarily match the core CPU clock frequency.
+  static double Frequency();
+
+ private:
+#if ABSL_USE_UNSCALED_CYCLECLOCK
+  static CycleClockSourceFunc LoadCycleClockSource();
+
+#ifdef NDEBUG
+#ifdef ABSL_INTERNAL_UNSCALED_CYCLECLOCK_FREQUENCY_IS_CPU_FREQUENCY
+  // Not debug mode and the UnscaledCycleClock frequency is the CPU
+  // frequency.  Scale the CycleClock to prevent overflow if someone
+  // tries to represent the time as cycles since the Unix epoch.
+  static constexpr int32_t kShift = 1;
+#else
+  // Not debug mode and the UnscaledCycleClock isn't operating at the
+  // raw CPU frequency. There is no need to do any scaling, so don't
+  // needlessly sacrifice precision.
+  static constexpr int32_t kShift = 0;
+#endif
+#else   // NDEBUG
+  // In debug mode use a different shift to discourage depending on a
+  // particular shift value.
+  static constexpr int32_t kShift = 2;
+#endif  // NDEBUG
+
+  static constexpr double kFrequencyScale = 1.0 / (1 << kShift);
+  ABSL_CONST_INIT static std::atomic<CycleClockSourceFunc> cycle_clock_source_;
+#endif  //  ABSL_USE_UNSCALED_CYCLECLOC
+
+  CycleClock() = delete;  // no instances
+  CycleClock(const CycleClock&) = delete;
+  CycleClock& operator=(const CycleClock&) = delete;
+
+  friend class CycleClockSource;
+};
+
+class CycleClockSource {
+ private:
+  // CycleClockSource::Register()
+  //
+  // Register a function that provides an alternate source for the unscaled CPU
+  // cycle count value. The source function must be async signal safe, must not
+  // call CycleClock::Now(), and must have a frequency that matches that of the
+  // unscaled clock used by CycleClock. A nullptr value resets CycleClock to use
+  // the default source.
+  static void Register(CycleClockSourceFunc source);
+};
+
+#if ABSL_USE_UNSCALED_CYCLECLOCK
+
+inline CycleClockSourceFunc CycleClock::LoadCycleClockSource() {
+#if !defined(__x86_64__)
+  // Optimize for the common case (no callback) by first doing a relaxed load;
+  // this is significantly faster on non-x86 platforms.
+  if (cycle_clock_source_.load(std::memory_order_relaxed) == nullptr) {
+    return nullptr;
+  }
+#endif  // !defined(__x86_64__)
+
+  // This corresponds to the store(std::memory_order_release) in
+  // CycleClockSource::Register, and makes sure that any updates made prior to
+  // registering the callback are visible to this thread before the callback
+  // is invoked.
+  return cycle_clock_source_.load(std::memory_order_acquire);
+}
+
+// Accessing globals in inlined code in Window DLLs is problematic.
+#ifndef _WIN32
+inline int64_t CycleClock::Now() {
+  auto fn = LoadCycleClockSource();
+  if (fn == nullptr) {
+    return base_internal::UnscaledCycleClock::Now() >> kShift;
+  }
+  return fn() >> kShift;
+}
+#endif
+
+inline double CycleClock::Frequency() {
+  return kFrequencyScale * base_internal::UnscaledCycleClock::Frequency();
+}
+
+#endif  // ABSL_USE_UNSCALED_CYCLECLOCK
+
+}  // namespace base_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_BASE_INTERNAL_CYCLECLOCK_H_
--- a/include/absl/base/internal/direct_mmap.h
+++ b/include/absl/base/internal/direct_mmap.h
@ -0,0 +1,169 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// Functions for directly invoking mmap() via syscall, avoiding the case where
+// mmap() has been locally overridden.
+
+#ifndef ABSL_BASE_INTERNAL_DIRECT_MMAP_H_
+#define ABSL_BASE_INTERNAL_DIRECT_MMAP_H_
+
+#include "absl/base/config.h"
+
+#ifdef ABSL_HAVE_MMAP
+
+#include <sys/mman.h>
+
+#ifdef __linux__
+
+#include <sys/types.h>
+#ifdef __BIONIC__
+#include <sys/syscall.h>
+#else
+#include <syscall.h>
+#endif
+
+#include <linux/unistd.h>
+#include <unistd.h>
+#include <cerrno>
+#include <cstdarg>
+#include <cstdint>
+
+#ifdef __mips__
+// Include definitions of the ABI currently in use.
+#if defined(__BIONIC__) || !defined(__GLIBC__)
+// Android doesn't have sgidefs.h, but does have asm/sgidefs.h, which has the
+// definitions we need.
+#include <asm/sgidefs.h>
+#else
+#include <sgidefs.h>
+#endif  // __BIONIC__ || !__GLIBC__
+#endif  // __mips__
+
+// SYS_mmap and SYS_munmap are not defined in Android.
+#ifdef __BIONIC__
+extern "C" void* __mmap2(void*, size_t, int, int, int, size_t);
+#if defined(__NR_mmap) && !defined(SYS_mmap)
+#define SYS_mmap __NR_mmap
+#endif
+#ifndef SYS_munmap
+#define SYS_munmap __NR_munmap
+#endif
+#endif  // __BIONIC__
+
+#if defined(__NR_mmap2) && !defined(SYS_mmap2)
+#define SYS_mmap2 __NR_mmap2
+#endif
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace base_internal {
+
+// Platform specific logic extracted from
+// https://chromium.googlesource.com/linux-syscall-support/+/master/linux_syscall_support.h
+inline void* DirectMmap(void* start, size_t length, int prot, int flags, int fd,
+                        off64_t offset) noexcept {
+#if defined(__i386__) || defined(__ARM_ARCH_3__) || defined(__ARM_EABI__) || \
+    defined(__m68k__) || defined(__sh__) ||                                  \
+    (defined(__hppa__) && !defined(__LP64__)) ||                             \
+    (defined(__mips__) && _MIPS_SIM == _MIPS_SIM_ABI32) ||                   \
+    (defined(__PPC__) && !defined(__PPC64__)) ||                             \
+    (defined(__riscv) && __riscv_xlen == 32) ||                              \
+    (defined(__s390__) && !defined(__s390x__)) ||                            \
+    (defined(__sparc__) && !defined(__arch64__))
+  // On these architectures, implement mmap with mmap2.
+  static int pagesize = 0;
+  if (pagesize == 0) {
+#if defined(__wasm__) || defined(__asmjs__)
+    pagesize = getpagesize();
+#else
+    pagesize = sysconf(_SC_PAGESIZE);
+#endif
+  }
+  if (offset < 0 || offset % pagesize != 0) {
+    errno = EINVAL;
+    return MAP_FAILED;
+  }
+#ifdef __BIONIC__
+  // SYS_mmap2 has problems on Android API level <= 16.
+  // Workaround by invoking __mmap2() instead.
+  return __mmap2(start, length, prot, flags, fd, offset / pagesize);
+#else
+  return reinterpret_cast<void*>(
+      syscall(SYS_mmap2, start, length, prot, flags, fd,
+              static_cast<off_t>(offset / pagesize)));
+#endif
+#elif defined(__s390x__)
+  // On s390x, mmap() arguments are passed in memory.
+  unsigned long buf[6] = {reinterpret_cast<unsigned long>(start),  // NOLINT
+                          static_cast<unsigned long>(length),      // NOLINT
+                          static_cast<unsigned long>(prot),        // NOLINT
+                          static_cast<unsigned long>(flags),       // NOLINT
+                          static_cast<unsigned long>(fd),          // NOLINT
+                          static_cast<unsigned long>(offset)};     // NOLINT
+  return reinterpret_cast<void*>(syscall(SYS_mmap, buf));
+#elif defined(__x86_64__)
+// The x32 ABI has 32 bit longs, but the syscall interface is 64 bit.
+// We need to explicitly cast to an unsigned 64 bit type to avoid implicit
+// sign extension.  We can't cast pointers directly because those are
+// 32 bits, and gcc will dump ugly warnings about casting from a pointer
+// to an integer of a different size. We also need to make sure __off64_t
+// isn't truncated to 32-bits under x32.
+#define MMAP_SYSCALL_ARG(x) ((uint64_t)(uintptr_t)(x))
+  return reinterpret_cast<void*>(
+      syscall(SYS_mmap, MMAP_SYSCALL_ARG(start), MMAP_SYSCALL_ARG(length),
+              MMAP_SYSCALL_ARG(prot), MMAP_SYSCALL_ARG(flags),
+              MMAP_SYSCALL_ARG(fd), static_cast<uint64_t>(offset)));
+#undef MMAP_SYSCALL_ARG
+#else  // Remaining 64-bit aritectures.
+  static_assert(sizeof(unsigned long) == 8, "Platform is not 64-bit");
+  return reinterpret_cast<void*>(
+      syscall(SYS_mmap, start, length, prot, flags, fd, offset));
+#endif
+}
+
+inline int DirectMunmap(void* start, size_t length) {
+  return static_cast<int>(syscall(SYS_munmap, start, length));
+}
+
+}  // namespace base_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#else  // !__linux__
+
+// For non-linux platforms where we have mmap, just dispatch directly to the
+// actual mmap()/munmap() methods.
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace base_internal {
+
+inline void* DirectMmap(void* start, size_t length, int prot, int flags, int fd,
+                        off_t offset) {
+  return mmap(start, length, prot, flags, fd, offset);
+}
+
+inline int DirectMunmap(void* start, size_t length) {
+  return munmap(start, length);
+}
+
+}  // namespace base_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // __linux__
+
+#endif  // ABSL_HAVE_MMAP
+
+#endif  // ABSL_BASE_INTERNAL_DIRECT_MMAP_H_
--- a/include/absl/base/internal/dynamic_annotations.h
+++ b/include/absl/base/internal/dynamic_annotations.h
@ -0,0 +1,398 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// This file defines dynamic annotations for use with dynamic analysis tool
+// such as valgrind, PIN, etc.
+//
+// Dynamic annotation is a source code annotation that affects the generated
+// code (that is, the annotation is not a comment). Each such annotation is
+// attached to a particular instruction and/or to a particular object (address)
+// in the program.
+//
+// The annotations that should be used by users are macros in all upper-case
+// (e.g., ANNOTATE_THREAD_NAME).
+//
+// Actual implementation of these macros may differ depending on the dynamic
+// analysis tool being used.
+//
+// This file supports the following configurations:
+// - Dynamic Annotations enabled (with static thread-safety warnings disabled).
+//   In this case, macros expand to functions implemented by Thread Sanitizer,
+//   when building with TSan. When not provided an external implementation,
+//   dynamic_annotations.cc provides no-op implementations.
+//
+// - Static Clang thread-safety warnings enabled.
+//   When building with a Clang compiler that supports thread-safety warnings,
+//   a subset of annotations can be statically-checked at compile-time. We
+//   expand these macros to static-inline functions that can be analyzed for
+//   thread-safety, but afterwards elided when building the final binary.
+//
+// - All annotations are disabled.
+//   If neither Dynamic Annotations nor Clang thread-safety warnings are
+//   enabled, then all annotation-macros expand to empty.
+
+#ifndef ABSL_BASE_INTERNAL_DYNAMIC_ANNOTATIONS_H_
+#define ABSL_BASE_INTERNAL_DYNAMIC_ANNOTATIONS_H_
+
+#include <stddef.h>
+
+#include "absl/base/config.h"
+
+// -------------------------------------------------------------------------
+// Decide which features are enabled
+
+#ifndef DYNAMIC_ANNOTATIONS_ENABLED
+#define DYNAMIC_ANNOTATIONS_ENABLED 0
+#endif
+
+#if defined(__clang__) && !defined(SWIG)
+#define ABSL_INTERNAL_IGNORE_READS_ATTRIBUTE_ENABLED 1
+#endif
+
+#if DYNAMIC_ANNOTATIONS_ENABLED != 0
+
+#define ABSL_INTERNAL_RACE_ANNOTATIONS_ENABLED 1
+#define ABSL_INTERNAL_READS_ANNOTATIONS_ENABLED 1
+#define ABSL_INTERNAL_WRITES_ANNOTATIONS_ENABLED 1
+#define ABSL_INTERNAL_ANNOTALYSIS_ENABLED 0
+#define ABSL_INTERNAL_READS_WRITES_ANNOTATIONS_ENABLED 1
+
+#else
+
+#define ABSL_INTERNAL_RACE_ANNOTATIONS_ENABLED 0
+#define ABSL_INTERNAL_READS_ANNOTATIONS_ENABLED 0
+#define ABSL_INTERNAL_WRITES_ANNOTATIONS_ENABLED 0
+
+// Clang provides limited support for static thread-safety analysis through a
+// feature called Annotalysis. We configure macro-definitions according to
+// whether Annotalysis support is available. When running in opt-mode, GCC
+// will issue a warning, if these attributes are compiled. Only include them
+// when compiling using Clang.
+
+// ANNOTALYSIS_ENABLED == 1 when IGNORE_READ_ATTRIBUTE_ENABLED == 1
+#define ABSL_INTERNAL_ANNOTALYSIS_ENABLED \
+  defined(ABSL_INTERNAL_IGNORE_READS_ATTRIBUTE_ENABLED)
+// Read/write annotations are enabled in Annotalysis mode; disabled otherwise.
+#define ABSL_INTERNAL_READS_WRITES_ANNOTATIONS_ENABLED \
+  ABSL_INTERNAL_ANNOTALYSIS_ENABLED
+#endif
+
+// Memory annotations are also made available to LLVM's Memory Sanitizer
+#if defined(ABSL_HAVE_MEMORY_SANITIZER) && !defined(__native_client__)
+#define ABSL_INTERNAL_MEMORY_ANNOTATIONS_ENABLED 1
+#endif
+
+#ifndef ABSL_INTERNAL_MEMORY_ANNOTATIONS_ENABLED
+#define ABSL_INTERNAL_MEMORY_ANNOTATIONS_ENABLED 0
+#endif
+
+#ifdef __cplusplus
+#define ABSL_INTERNAL_BEGIN_EXTERN_C extern "C" {
+#define ABSL_INTERNAL_END_EXTERN_C }  // extern "C"
+#define ABSL_INTERNAL_GLOBAL_SCOPED(F) ::F
+#define ABSL_INTERNAL_STATIC_INLINE inline
+#else
+#define ABSL_INTERNAL_BEGIN_EXTERN_C  // empty
+#define ABSL_INTERNAL_END_EXTERN_C    // empty
+#define ABSL_INTERNAL_GLOBAL_SCOPED(F) F
+#define ABSL_INTERNAL_STATIC_INLINE static inline
+#endif
+
+// -------------------------------------------------------------------------
+// Define race annotations.
+
+#if ABSL_INTERNAL_RACE_ANNOTATIONS_ENABLED == 1
+
+// -------------------------------------------------------------
+// Annotations that suppress errors. It is usually better to express the
+// program's synchronization using the other annotations, but these can be used
+// when all else fails.
+
+// Report that we may have a benign race at `pointer`, with size
+// "sizeof(*(pointer))". `pointer` must be a non-void* pointer. Insert at the
+// point where `pointer` has been allocated, preferably close to the point
+// where the race happens. See also ANNOTATE_BENIGN_RACE_STATIC.
+#define ANNOTATE_BENIGN_RACE(pointer, description)     \
+  ABSL_INTERNAL_GLOBAL_SCOPED(AnnotateBenignRaceSized) \
+  (__FILE__, __LINE__, pointer, sizeof(*(pointer)), description)
+
+// Same as ANNOTATE_BENIGN_RACE(`address`, `description`), but applies to
+// the memory range [`address`, `address`+`size`).
+#define ANNOTATE_BENIGN_RACE_SIZED(address, size, description) \
+  ABSL_INTERNAL_GLOBAL_SCOPED(AnnotateBenignRaceSized)         \
+  (__FILE__, __LINE__, address, size, description)
+
+// Enable (`enable`!=0) or disable (`enable`==0) race detection for all threads.
+// This annotation could be useful if you want to skip expensive race analysis
+// during some period of program execution, e.g. during initialization.
+#define ANNOTATE_ENABLE_RACE_DETECTION(enable)             \
+  ABSL_INTERNAL_GLOBAL_SCOPED(AnnotateEnableRaceDetection) \
+  (__FILE__, __LINE__, enable)
+
+// -------------------------------------------------------------
+// Annotations useful for debugging.
+
+// Report the current thread `name` to a race detector.
+#define ANNOTATE_THREAD_NAME(name) \
+  ABSL_INTERNAL_GLOBAL_SCOPED(AnnotateThreadName)(__FILE__, __LINE__, name)
+
+// -------------------------------------------------------------
+// Annotations useful when implementing locks. They are not normally needed by
+// modules that merely use locks. The `lock` argument is a pointer to the lock
+// object.
+
+// Report that a lock has been created at address `lock`.
+#define ANNOTATE_RWLOCK_CREATE(lock) \
+  ABSL_INTERNAL_GLOBAL_SCOPED(AnnotateRWLockCreate)(__FILE__, __LINE__, lock)
+
+// Report that a linker initialized lock has been created at address `lock`.
+#ifdef ABSL_HAVE_THREAD_SANITIZER
+#define ANNOTATE_RWLOCK_CREATE_STATIC(lock)               \
+  ABSL_INTERNAL_GLOBAL_SCOPED(AnnotateRWLockCreateStatic) \
+  (__FILE__, __LINE__, lock)
+#else
+#define ANNOTATE_RWLOCK_CREATE_STATIC(lock) ANNOTATE_RWLOCK_CREATE(lock)
+#endif
+
+// Report that the lock at address `lock` is about to be destroyed.
+#define ANNOTATE_RWLOCK_DESTROY(lock) \
+  ABSL_INTERNAL_GLOBAL_SCOPED(AnnotateRWLockDestroy)(__FILE__, __LINE__, lock)
+
+// Report that the lock at address `lock` has been acquired.
+// `is_w`=1 for writer lock, `is_w`=0 for reader lock.
+#define ANNOTATE_RWLOCK_ACQUIRED(lock, is_w)          \
+  ABSL_INTERNAL_GLOBAL_SCOPED(AnnotateRWLockAcquired) \
+  (__FILE__, __LINE__, lock, is_w)
+
+// Report that the lock at address `lock` is about to be released.
+// `is_w`=1 for writer lock, `is_w`=0 for reader lock.
+#define ANNOTATE_RWLOCK_RELEASED(lock, is_w)          \
+  ABSL_INTERNAL_GLOBAL_SCOPED(AnnotateRWLockReleased) \
+  (__FILE__, __LINE__, lock, is_w)
+
+// Apply ANNOTATE_BENIGN_RACE_SIZED to a static variable `static_var`.
+#define ANNOTATE_BENIGN_RACE_STATIC(static_var, description)      \
+  namespace {                                                     \
+  class static_var##_annotator {                                  \
+   public:                                                        \
+    static_var##_annotator() {                                    \
+      ANNOTATE_BENIGN_RACE_SIZED(&static_var, sizeof(static_var), \
+                                 #static_var ": " description);   \
+    }                                                             \
+  };                                                              \
+  static static_var##_annotator the##static_var##_annotator;      \
+  }  // namespace
+
+#else  // ABSL_INTERNAL_RACE_ANNOTATIONS_ENABLED == 0
+
+#define ANNOTATE_RWLOCK_CREATE(lock)                            // empty
+#define ANNOTATE_RWLOCK_CREATE_STATIC(lock)                     // empty
+#define ANNOTATE_RWLOCK_DESTROY(lock)                           // empty
+#define ANNOTATE_RWLOCK_ACQUIRED(lock, is_w)                    // empty
+#define ANNOTATE_RWLOCK_RELEASED(lock, is_w)                    // empty
+#define ANNOTATE_BENIGN_RACE(address, description)              // empty
+#define ANNOTATE_BENIGN_RACE_SIZED(address, size, description)  // empty
+#define ANNOTATE_THREAD_NAME(name)                              // empty
+#define ANNOTATE_ENABLE_RACE_DETECTION(enable)                  // empty
+#define ANNOTATE_BENIGN_RACE_STATIC(static_var, description)    // empty
+
+#endif  // ABSL_INTERNAL_RACE_ANNOTATIONS_ENABLED
+
+// -------------------------------------------------------------------------
+// Define memory annotations.
+
+#if ABSL_INTERNAL_MEMORY_ANNOTATIONS_ENABLED == 1
+
+#include <sanitizer/msan_interface.h>
+
+#define ANNOTATE_MEMORY_IS_INITIALIZED(address, size) \
+  __msan_unpoison(address, size)
+
+#define ANNOTATE_MEMORY_IS_UNINITIALIZED(address, size) \
+  __msan_allocated_memory(address, size)
+
+#else  // ABSL_INTERNAL_MEMORY_ANNOTATIONS_ENABLED == 0
+
+#if DYNAMIC_ANNOTATIONS_ENABLED == 1
+#define ANNOTATE_MEMORY_IS_INITIALIZED(address, size) \
+  do {                                                \
+    (void)(address);                                  \
+    (void)(size);                                     \
+  } while (0)
+#define ANNOTATE_MEMORY_IS_UNINITIALIZED(address, size) \
+  do {                                                  \
+    (void)(address);                                    \
+    (void)(size);                                       \
+  } while (0)
+#else
+#define ANNOTATE_MEMORY_IS_INITIALIZED(address, size)    // empty
+#define ANNOTATE_MEMORY_IS_UNINITIALIZED(address, size)  // empty
+#endif
+
+#endif  // ABSL_INTERNAL_MEMORY_ANNOTATIONS_ENABLED
+
+// -------------------------------------------------------------------------
+// Define IGNORE_READS_BEGIN/_END attributes.
+
+#if defined(ABSL_INTERNAL_IGNORE_READS_ATTRIBUTE_ENABLED)
+
+#define ABSL_INTERNAL_IGNORE_READS_BEGIN_ATTRIBUTE \
+  __attribute((exclusive_lock_function("*")))
+#define ABSL_INTERNAL_IGNORE_READS_END_ATTRIBUTE \
+  __attribute((unlock_function("*")))
+
+#else  // !defined(ABSL_INTERNAL_IGNORE_READS_ATTRIBUTE_ENABLED)
+
+#define ABSL_INTERNAL_IGNORE_READS_BEGIN_ATTRIBUTE  // empty
+#define ABSL_INTERNAL_IGNORE_READS_END_ATTRIBUTE    // empty
+
+#endif  // defined(ABSL_INTERNAL_IGNORE_READS_ATTRIBUTE_ENABLED)
+
+// -------------------------------------------------------------------------
+// Define IGNORE_READS_BEGIN/_END annotations.
+
+#if ABSL_INTERNAL_READS_ANNOTATIONS_ENABLED == 1
+
+// Request the analysis tool to ignore all reads in the current thread until
+// ANNOTATE_IGNORE_READS_END is called. Useful to ignore intentional racey
+// reads, while still checking other reads and all writes.
+// See also ANNOTATE_UNPROTECTED_READ.
+#define ANNOTATE_IGNORE_READS_BEGIN() \
+  ABSL_INTERNAL_GLOBAL_SCOPED(AnnotateIgnoreReadsBegin)(__FILE__, __LINE__)
+
+// Stop ignoring reads.
+#define ANNOTATE_IGNORE_READS_END() \
+  ABSL_INTERNAL_GLOBAL_SCOPED(AnnotateIgnoreReadsEnd)(__FILE__, __LINE__)
+
+#elif defined(ABSL_INTERNAL_ANNOTALYSIS_ENABLED)
+
+// When Annotalysis is enabled without Dynamic Annotations, the use of
+// static-inline functions allows the annotations to be read at compile-time,
+// while still letting the compiler elide the functions from the final build.
+//
+// TODO(delesley) -- The exclusive lock here ignores writes as well, but
+// allows IGNORE_READS_AND_WRITES to work properly.
+
+#define ANNOTATE_IGNORE_READS_BEGIN() \
+  ABSL_INTERNAL_GLOBAL_SCOPED(AbslInternalAnnotateIgnoreReadsBegin)()
+
+#define ANNOTATE_IGNORE_READS_END() \
+  ABSL_INTERNAL_GLOBAL_SCOPED(AbslInternalAnnotateIgnoreReadsEnd)()
+
+#else
+
+#define ANNOTATE_IGNORE_READS_BEGIN()  // empty
+#define ANNOTATE_IGNORE_READS_END()    // empty
+
+#endif
+
+// -------------------------------------------------------------------------
+// Define IGNORE_WRITES_BEGIN/_END annotations.
+
+#if ABSL_INTERNAL_WRITES_ANNOTATIONS_ENABLED == 1
+
+// Similar to ANNOTATE_IGNORE_READS_BEGIN, but ignore writes instead.
+#define ANNOTATE_IGNORE_WRITES_BEGIN() \
+  ABSL_INTERNAL_GLOBAL_SCOPED(AnnotateIgnoreWritesBegin)(__FILE__, __LINE__)
+
+// Stop ignoring writes.
+#define ANNOTATE_IGNORE_WRITES_END() \
+  ABSL_INTERNAL_GLOBAL_SCOPED(AnnotateIgnoreWritesEnd)(__FILE__, __LINE__)
+
+#else
+
+#define ANNOTATE_IGNORE_WRITES_BEGIN()  // empty
+#define ANNOTATE_IGNORE_WRITES_END()    // empty
+
+#endif
+
+// -------------------------------------------------------------------------
+// Define the ANNOTATE_IGNORE_READS_AND_WRITES_* annotations using the more
+// primitive annotations defined above.
+//
+//     Instead of doing
+//        ANNOTATE_IGNORE_READS_BEGIN();
+//        ... = x;
+//        ANNOTATE_IGNORE_READS_END();
+//     one can use
+//        ... = ANNOTATE_UNPROTECTED_READ(x);
+
+#if defined(ABSL_INTERNAL_READS_WRITES_ANNOTATIONS_ENABLED)
+
+// Start ignoring all memory accesses (both reads and writes).
+#define ANNOTATE_IGNORE_READS_AND_WRITES_BEGIN() \
+  do {                                           \
+    ANNOTATE_IGNORE_READS_BEGIN();               \
+    ANNOTATE_IGNORE_WRITES_BEGIN();              \
+  } while (0)
+
+// Stop ignoring both reads and writes.
+#define ANNOTATE_IGNORE_READS_AND_WRITES_END() \
+  do {                                         \
+    ANNOTATE_IGNORE_WRITES_END();              \
+    ANNOTATE_IGNORE_READS_END();               \
+  } while (0)
+
+#ifdef __cplusplus
+// ANNOTATE_UNPROTECTED_READ is the preferred way to annotate racey reads.
+#define ANNOTATE_UNPROTECTED_READ(x) \
+  absl::base_internal::AnnotateUnprotectedRead(x)
+
+#endif
+
+#else
+
+#define ANNOTATE_IGNORE_READS_AND_WRITES_BEGIN()  // empty
+#define ANNOTATE_IGNORE_READS_AND_WRITES_END()    // empty
+#define ANNOTATE_UNPROTECTED_READ(x) (x)
+
+#endif
+
+// -------------------------------------------------------------------------
+// Address sanitizer annotations
+
+#ifdef ABSL_HAVE_ADDRESS_SANITIZER
+// Describe the current state of a contiguous container such as e.g.
+// std::vector or std::string. For more details see
+// sanitizer/common_interface_defs.h, which is provided by the compiler.
+#include <sanitizer/common_interface_defs.h>
+
+#define ANNOTATE_CONTIGUOUS_CONTAINER(beg, end, old_mid, new_mid) \
+  __sanitizer_annotate_contiguous_container(beg, end, old_mid, new_mid)
+#define ADDRESS_SANITIZER_REDZONE(name)    \
+  struct {                                 \
+    char x[8] __attribute__((aligned(8))); \
+  } name
+
+#else
+
+#define ANNOTATE_CONTIGUOUS_CONTAINER(beg, end, old_mid, new_mid)
+#define ADDRESS_SANITIZER_REDZONE(name) static_assert(true, "")
+
+#endif  // ABSL_HAVE_ADDRESS_SANITIZER
+
+// -------------------------------------------------------------------------
+// Undefine the macros intended only for this file.
+
+#undef ABSL_INTERNAL_RACE_ANNOTATIONS_ENABLED
+#undef ABSL_INTERNAL_MEMORY_ANNOTATIONS_ENABLED
+#undef ABSL_INTERNAL_READS_ANNOTATIONS_ENABLED
+#undef ABSL_INTERNAL_WRITES_ANNOTATIONS_ENABLED
+#undef ABSL_INTERNAL_ANNOTALYSIS_ENABLED
+#undef ABSL_INTERNAL_READS_WRITES_ANNOTATIONS_ENABLED
+#undef ABSL_INTERNAL_BEGIN_EXTERN_C
+#undef ABSL_INTERNAL_END_EXTERN_C
+#undef ABSL_INTERNAL_STATIC_INLINE
+
+#endif  // ABSL_BASE_INTERNAL_DYNAMIC_ANNOTATIONS_H_
--- a/include/absl/base/internal/endian.h
+++ b/include/absl/base/internal/endian.h
@ -0,0 +1,282 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+#ifndef ABSL_BASE_INTERNAL_ENDIAN_H_
+#define ABSL_BASE_INTERNAL_ENDIAN_H_
+
+#include <cstdint>
+#include <cstdlib>
+
+#include "absl/base/casts.h"
+#include "absl/base/config.h"
+#include "absl/base/internal/unaligned_access.h"
+#include "absl/base/port.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+
+inline uint64_t gbswap_64(uint64_t host_int) {
+#if ABSL_HAVE_BUILTIN(__builtin_bswap64) || defined(__GNUC__)
+  return __builtin_bswap64(host_int);
+#elif defined(_MSC_VER)
+  return _byteswap_uint64(host_int);
+#else
+  return (((host_int & uint64_t{0xFF}) << 56) |
+          ((host_int & uint64_t{0xFF00}) << 40) |
+          ((host_int & uint64_t{0xFF0000}) << 24) |
+          ((host_int & uint64_t{0xFF000000}) << 8) |
+          ((host_int & uint64_t{0xFF00000000}) >> 8) |
+          ((host_int & uint64_t{0xFF0000000000}) >> 24) |
+          ((host_int & uint64_t{0xFF000000000000}) >> 40) |
+          ((host_int & uint64_t{0xFF00000000000000}) >> 56));
+#endif
+}
+
+inline uint32_t gbswap_32(uint32_t host_int) {
+#if ABSL_HAVE_BUILTIN(__builtin_bswap32) || defined(__GNUC__)
+  return __builtin_bswap32(host_int);
+#elif defined(_MSC_VER)
+  return _byteswap_ulong(host_int);
+#else
+  return (((host_int & uint32_t{0xFF}) << 24) |
+          ((host_int & uint32_t{0xFF00}) << 8) |
+          ((host_int & uint32_t{0xFF0000}) >> 8) |
+          ((host_int & uint32_t{0xFF000000}) >> 24));
+#endif
+}
+
+inline uint16_t gbswap_16(uint16_t host_int) {
+#if ABSL_HAVE_BUILTIN(__builtin_bswap16) || defined(__GNUC__)
+  return __builtin_bswap16(host_int);
+#elif defined(_MSC_VER)
+  return _byteswap_ushort(host_int);
+#else
+  return (((host_int & uint16_t{0xFF}) << 8) |
+          ((host_int & uint16_t{0xFF00}) >> 8));
+#endif
+}
+
+#ifdef ABSL_IS_LITTLE_ENDIAN
+
+// Portable definitions for htonl (host-to-network) and friends on little-endian
+// architectures.
+inline uint16_t ghtons(uint16_t x) { return gbswap_16(x); }
+inline uint32_t ghtonl(uint32_t x) { return gbswap_32(x); }
+inline uint64_t ghtonll(uint64_t x) { return gbswap_64(x); }
+
+#elif defined ABSL_IS_BIG_ENDIAN
+
+// Portable definitions for htonl (host-to-network) etc on big-endian
+// architectures. These definitions are simpler since the host byte order is the
+// same as network byte order.
+inline uint16_t ghtons(uint16_t x) { return x; }
+inline uint32_t ghtonl(uint32_t x) { return x; }
+inline uint64_t ghtonll(uint64_t x) { return x; }
+
+#else
+#error \
+    "Unsupported byte order: Either ABSL_IS_BIG_ENDIAN or " \
+       "ABSL_IS_LITTLE_ENDIAN must be defined"
+#endif  // byte order
+
+inline uint16_t gntohs(uint16_t x) { return ghtons(x); }
+inline uint32_t gntohl(uint32_t x) { return ghtonl(x); }
+inline uint64_t gntohll(uint64_t x) { return ghtonll(x); }
+
+// Utilities to convert numbers between the current hosts's native byte
+// order and little-endian byte order
+//
+// Load/Store methods are alignment safe
+namespace little_endian {
+// Conversion functions.
+#ifdef ABSL_IS_LITTLE_ENDIAN
+
+inline uint16_t FromHost16(uint16_t x) { return x; }
+inline uint16_t ToHost16(uint16_t x) { return x; }
+
+inline uint32_t FromHost32(uint32_t x) { return x; }
+inline uint32_t ToHost32(uint32_t x) { return x; }
+
+inline uint64_t FromHost64(uint64_t x) { return x; }
+inline uint64_t ToHost64(uint64_t x) { return x; }
+
+inline constexpr bool IsLittleEndian() { return true; }
+
+#elif defined ABSL_IS_BIG_ENDIAN
+
+inline uint16_t FromHost16(uint16_t x) { return gbswap_16(x); }
+inline uint16_t ToHost16(uint16_t x) { return gbswap_16(x); }
+
+inline uint32_t FromHost32(uint32_t x) { return gbswap_32(x); }
+inline uint32_t ToHost32(uint32_t x) { return gbswap_32(x); }
+
+inline uint64_t FromHost64(uint64_t x) { return gbswap_64(x); }
+inline uint64_t ToHost64(uint64_t x) { return gbswap_64(x); }
+
+inline constexpr bool IsLittleEndian() { return false; }
+
+#endif /* ENDIAN */
+
+inline uint8_t FromHost(uint8_t x) { return x; }
+inline uint16_t FromHost(uint16_t x) { return FromHost16(x); }
+inline uint32_t FromHost(uint32_t x) { return FromHost32(x); }
+inline uint64_t FromHost(uint64_t x) { return FromHost64(x); }
+inline uint8_t ToHost(uint8_t x) { return x; }
+inline uint16_t ToHost(uint16_t x) { return ToHost16(x); }
+inline uint32_t ToHost(uint32_t x) { return ToHost32(x); }
+inline uint64_t ToHost(uint64_t x) { return ToHost64(x); }
+
+inline int8_t FromHost(int8_t x) { return x; }
+inline int16_t FromHost(int16_t x) {
+  return bit_cast<int16_t>(FromHost16(bit_cast<uint16_t>(x)));
+}
+inline int32_t FromHost(int32_t x) {
+  return bit_cast<int32_t>(FromHost32(bit_cast<uint32_t>(x)));
+}
+inline int64_t FromHost(int64_t x) {
+  return bit_cast<int64_t>(FromHost64(bit_cast<uint64_t>(x)));
+}
+inline int8_t ToHost(int8_t x) { return x; }
+inline int16_t ToHost(int16_t x) {
+  return bit_cast<int16_t>(ToHost16(bit_cast<uint16_t>(x)));
+}
+inline int32_t ToHost(int32_t x) {
+  return bit_cast<int32_t>(ToHost32(bit_cast<uint32_t>(x)));
+}
+inline int64_t ToHost(int64_t x) {
+  return bit_cast<int64_t>(ToHost64(bit_cast<uint64_t>(x)));
+}
+
+// Functions to do unaligned loads and stores in little-endian order.
+inline uint16_t Load16(const void *p) {
+  return ToHost16(ABSL_INTERNAL_UNALIGNED_LOAD16(p));
+}
+
+inline void Store16(void *p, uint16_t v) {
+  ABSL_INTERNAL_UNALIGNED_STORE16(p, FromHost16(v));
+}
+
+inline uint32_t Load32(const void *p) {
+  return ToHost32(ABSL_INTERNAL_UNALIGNED_LOAD32(p));
+}
+
+inline void Store32(void *p, uint32_t v) {
+  ABSL_INTERNAL_UNALIGNED_STORE32(p, FromHost32(v));
+}
+
+inline uint64_t Load64(const void *p) {
+  return ToHost64(ABSL_INTERNAL_UNALIGNED_LOAD64(p));
+}
+
+inline void Store64(void *p, uint64_t v) {
+  ABSL_INTERNAL_UNALIGNED_STORE64(p, FromHost64(v));
+}
+
+}  // namespace little_endian
+
+// Utilities to convert numbers between the current hosts's native byte
+// order and big-endian byte order (same as network byte order)
+//
+// Load/Store methods are alignment safe
+namespace big_endian {
+#ifdef ABSL_IS_LITTLE_ENDIAN
+
+inline uint16_t FromHost16(uint16_t x) { return gbswap_16(x); }
+inline uint16_t ToHost16(uint16_t x) { return gbswap_16(x); }
+
+inline uint32_t FromHost32(uint32_t x) { return gbswap_32(x); }
+inline uint32_t ToHost32(uint32_t x) { return gbswap_32(x); }
+
+inline uint64_t FromHost64(uint64_t x) { return gbswap_64(x); }
+inline uint64_t ToHost64(uint64_t x) { return gbswap_64(x); }
+
+inline constexpr bool IsLittleEndian() { return true; }
+
+#elif defined ABSL_IS_BIG_ENDIAN
+
+inline uint16_t FromHost16(uint16_t x) { return x; }
+inline uint16_t ToHost16(uint16_t x) { return x; }
+
+inline uint32_t FromHost32(uint32_t x) { return x; }
+inline uint32_t ToHost32(uint32_t x) { return x; }
+
+inline uint64_t FromHost64(uint64_t x) { return x; }
+inline uint64_t ToHost64(uint64_t x) { return x; }
+
+inline constexpr bool IsLittleEndian() { return false; }
+
+#endif /* ENDIAN */
+
+inline uint8_t FromHost(uint8_t x) { return x; }
+inline uint16_t FromHost(uint16_t x) { return FromHost16(x); }
+inline uint32_t FromHost(uint32_t x) { return FromHost32(x); }
+inline uint64_t FromHost(uint64_t x) { return FromHost64(x); }
+inline uint8_t ToHost(uint8_t x) { return x; }
+inline uint16_t ToHost(uint16_t x) { return ToHost16(x); }
+inline uint32_t ToHost(uint32_t x) { return ToHost32(x); }
+inline uint64_t ToHost(uint64_t x) { return ToHost64(x); }
+
+inline int8_t FromHost(int8_t x) { return x; }
+inline int16_t FromHost(int16_t x) {
+  return bit_cast<int16_t>(FromHost16(bit_cast<uint16_t>(x)));
+}
+inline int32_t FromHost(int32_t x) {
+  return bit_cast<int32_t>(FromHost32(bit_cast<uint32_t>(x)));
+}
+inline int64_t FromHost(int64_t x) {
+  return bit_cast<int64_t>(FromHost64(bit_cast<uint64_t>(x)));
+}
+inline int8_t ToHost(int8_t x) { return x; }
+inline int16_t ToHost(int16_t x) {
+  return bit_cast<int16_t>(ToHost16(bit_cast<uint16_t>(x)));
+}
+inline int32_t ToHost(int32_t x) {
+  return bit_cast<int32_t>(ToHost32(bit_cast<uint32_t>(x)));
+}
+inline int64_t ToHost(int64_t x) {
+  return bit_cast<int64_t>(ToHost64(bit_cast<uint64_t>(x)));
+}
+
+// Functions to do unaligned loads and stores in big-endian order.
+inline uint16_t Load16(const void *p) {
+  return ToHost16(ABSL_INTERNAL_UNALIGNED_LOAD16(p));
+}
+
+inline void Store16(void *p, uint16_t v) {
+  ABSL_INTERNAL_UNALIGNED_STORE16(p, FromHost16(v));
+}
+
+inline uint32_t Load32(const void *p) {
+  return ToHost32(ABSL_INTERNAL_UNALIGNED_LOAD32(p));
+}
+
+inline void Store32(void *p, uint32_t v) {
+  ABSL_INTERNAL_UNALIGNED_STORE32(p, FromHost32(v));
+}
+
+inline uint64_t Load64(const void *p) {
+  return ToHost64(ABSL_INTERNAL_UNALIGNED_LOAD64(p));
+}
+
+inline void Store64(void *p, uint64_t v) {
+  ABSL_INTERNAL_UNALIGNED_STORE64(p, FromHost64(v));
+}
+
+}  // namespace big_endian
+
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_BASE_INTERNAL_ENDIAN_H_
--- a/include/absl/base/internal/errno_saver.h
+++ b/include/absl/base/internal/errno_saver.h
@ -0,0 +1,43 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef ABSL_BASE_INTERNAL_ERRNO_SAVER_H_
+#define ABSL_BASE_INTERNAL_ERRNO_SAVER_H_
+
+#include <cerrno>
+
+#include "absl/base/config.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace base_internal {
+
+// `ErrnoSaver` captures the value of `errno` upon construction and restores it
+// upon deletion.  It is used in low-level code and must be super fast.  Do not
+// add instrumentation, even in debug modes.
+class ErrnoSaver {
+ public:
+  ErrnoSaver() : saved_errno_(errno) {}
+  ~ErrnoSaver() { errno = saved_errno_; }
+  int operator()() const { return saved_errno_; }
+
+ private:
+  const int saved_errno_;
+};
+
+}  // namespace base_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_BASE_INTERNAL_ERRNO_SAVER_H_
--- a/include/absl/base/internal/exception_safety_testing.h
+++ b/include/absl/base/internal/exception_safety_testing.h
--- a/include/absl/base/internal/exception_testing.h
+++ b/include/absl/base/internal/exception_testing.h
@ -0,0 +1,42 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Testing utilities for ABSL types which throw exceptions.
+
+#ifndef ABSL_BASE_INTERNAL_EXCEPTION_TESTING_H_
+#define ABSL_BASE_INTERNAL_EXCEPTION_TESTING_H_
+
+#include "gtest/gtest.h"
+#include "absl/base/config.h"
+
+// ABSL_BASE_INTERNAL_EXPECT_FAIL tests either for a specified thrown exception
+// if exceptions are enabled, or for death with a specified text in the error
+// message
+#ifdef ABSL_HAVE_EXCEPTIONS
+
+#define ABSL_BASE_INTERNAL_EXPECT_FAIL(expr, exception_t, text) \
+  EXPECT_THROW(expr, exception_t)
+
+#elif defined(__ANDROID__)
+// Android asserts do not log anywhere that gtest can currently inspect.
+// So we expect exit, but cannot match the message.
+#define ABSL_BASE_INTERNAL_EXPECT_FAIL(expr, exception_t, text) \
+  EXPECT_DEATH(expr, ".*")
+#else
+#define ABSL_BASE_INTERNAL_EXPECT_FAIL(expr, exception_t, text) \
+  EXPECT_DEATH_IF_SUPPORTED(expr, text)
+
+#endif
+
+#endif  // ABSL_BASE_INTERNAL_EXCEPTION_TESTING_H_
--- a/include/absl/base/internal/fast_type_id.h
+++ b/include/absl/base/internal/fast_type_id.h
@ -0,0 +1,50 @@
+//
+// Copyright 2020 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+#ifndef ABSL_BASE_INTERNAL_FAST_TYPE_ID_H_
+#define ABSL_BASE_INTERNAL_FAST_TYPE_ID_H_
+
+#include "absl/base/config.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace base_internal {
+
+template <typename Type>
+struct FastTypeTag {
+  constexpr static char dummy_var = 0;
+};
+
+#ifdef ABSL_INTERNAL_NEED_REDUNDANT_CONSTEXPR_DECL
+template <typename Type>
+constexpr char FastTypeTag<Type>::dummy_var;
+#endif
+
+// FastTypeId<Type>() evaluates at compile/link-time to a unique pointer for the
+// passed-in type. These are meant to be good match for keys into maps or
+// straight up comparisons.
+using FastTypeIdType = const void*;
+
+template <typename Type>
+constexpr inline FastTypeIdType FastTypeId() {
+  return &FastTypeTag<Type>::dummy_var;
+}
+
+}  // namespace base_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_BASE_INTERNAL_FAST_TYPE_ID_H_
--- a/include/absl/base/internal/hide_ptr.h
+++ b/include/absl/base/internal/hide_ptr.h
@ -0,0 +1,51 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef ABSL_BASE_INTERNAL_HIDE_PTR_H_
+#define ABSL_BASE_INTERNAL_HIDE_PTR_H_
+
+#include <cstdint>
+
+#include "absl/base/config.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace base_internal {
+
+// Arbitrary value with high bits set. Xor'ing with it is unlikely
+// to map one valid pointer to another valid pointer.
+constexpr uintptr_t HideMask() {
+  return (uintptr_t{0xF03A5F7BU} << (sizeof(uintptr_t) - 4) * 8) | 0xF03A5F7BU;
+}
+
+// Hide a pointer from the leak checker. For internal use only.
+// Differs from absl::IgnoreLeak(ptr) in that absl::IgnoreLeak(ptr) causes ptr
+// and all objects reachable from ptr to be ignored by the leak checker.
+template <class T>
+inline uintptr_t HidePtr(T* ptr) {
+  return reinterpret_cast<uintptr_t>(ptr) ^ HideMask();
+}
+
+// Return a pointer that has been hidden from the leak checker.
+// For internal use only.
+template <class T>
+inline T* UnhidePtr(uintptr_t hidden) {
+  return reinterpret_cast<T*>(hidden ^ HideMask());
+}
+
+}  // namespace base_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_BASE_INTERNAL_HIDE_PTR_H_
--- a/include/absl/base/internal/identity.h
+++ b/include/absl/base/internal/identity.h
@ -0,0 +1,37 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+#ifndef ABSL_BASE_INTERNAL_IDENTITY_H_
+#define ABSL_BASE_INTERNAL_IDENTITY_H_
+
+#include "absl/base/config.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace internal {
+
+template <typename T>
+struct identity {
+  typedef T type;
+};
+
+template <typename T>
+using identity_t = typename identity<T>::type;
+
+}  // namespace internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_BASE_INTERNAL_IDENTITY_H_
--- a/include/absl/base/internal/inline_variable.h
+++ b/include/absl/base/internal/inline_variable.h
@ -0,0 +1,107 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef ABSL_BASE_INTERNAL_INLINE_VARIABLE_EMULATION_H_
+#define ABSL_BASE_INTERNAL_INLINE_VARIABLE_EMULATION_H_
+
+#include <type_traits>
+
+#include "absl/base/internal/identity.h"
+
+// File:
+//   This file define a macro that allows the creation of or emulation of C++17
+//   inline variables based on whether or not the feature is supported.
+
+////////////////////////////////////////////////////////////////////////////////
+// Macro: ABSL_INTERNAL_INLINE_CONSTEXPR(type, name, init)
+//
+// Description:
+//   Expands to the equivalent of an inline constexpr instance of the specified
+//   `type` and `name`, initialized to the value `init`. If the compiler being
+//   used is detected as supporting actual inline variables as a language
+//   feature, then the macro expands to an actual inline variable definition.
+//
+// Requires:
+//   `type` is a type that is usable in an extern variable declaration.
+//
+// Requires: `name` is a valid identifier
+//
+// Requires:
+//   `init` is an expression that can be used in the following definition:
+//     constexpr type name = init;
+//
+// Usage:
+//
+//   // Equivalent to: `inline constexpr size_t variant_npos = -1;`
+//   ABSL_INTERNAL_INLINE_CONSTEXPR(size_t, variant_npos, -1);
+//
+// Differences in implementation:
+//   For a direct, language-level inline variable, decltype(name) will be the
+//   type that was specified along with const qualification, whereas for
+//   emulated inline variables, decltype(name) may be different (in practice
+//   it will likely be a reference type).
+////////////////////////////////////////////////////////////////////////////////
+
+#ifdef __cpp_inline_variables
+
+// Clang's -Wmissing-variable-declarations option erroneously warned that
+// inline constexpr objects need to be pre-declared. This has now been fixed,
+// but we will need to support this workaround for people building with older
+// versions of clang.
+//
+// Bug: https://bugs.llvm.org/show_bug.cgi?id=35862
+//
+// Note:
+//   identity_t is used here so that the const and name are in the
+//   appropriate place for pointer types, reference types, function pointer
+//   types, etc..
+#if defined(__clang__)
+#define ABSL_INTERNAL_EXTERN_DECL(type, name) \
+  extern const ::absl::internal::identity_t<type> name;
+#else  // Otherwise, just define the macro to do nothing.
+#define ABSL_INTERNAL_EXTERN_DECL(type, name)
+#endif  // defined(__clang__)
+
+// See above comment at top of file for details.
+#define ABSL_INTERNAL_INLINE_CONSTEXPR(type, name, init) \
+  ABSL_INTERNAL_EXTERN_DECL(type, name)                  \
+  inline constexpr ::absl::internal::identity_t<type> name = init
+
+#else
+
+// See above comment at top of file for details.
+//
+// Note:
+//   identity_t is used here so that the const and name are in the
+//   appropriate place for pointer types, reference types, function pointer
+//   types, etc..
+#define ABSL_INTERNAL_INLINE_CONSTEXPR(var_type, name, init)                  \
+  template <class /*AbslInternalDummy*/ = void>                               \
+  struct AbslInternalInlineVariableHolder##name {                             \
+    static constexpr ::absl::internal::identity_t<var_type> kInstance = init; \
+  };                                                                          \
+                                                                              \
+  template <class AbslInternalDummy>                                          \
+  constexpr ::absl::internal::identity_t<var_type>                            \
+      AbslInternalInlineVariableHolder##name<AbslInternalDummy>::kInstance;   \
+                                                                              \
+  static constexpr const ::absl::internal::identity_t<var_type>&              \
+      name = /* NOLINT */                                                     \
+      AbslInternalInlineVariableHolder##name<>::kInstance;                    \
+  static_assert(sizeof(void (*)(decltype(name))) != 0,                        \
+                "Silence unused variable warnings.")
+
+#endif  // __cpp_inline_variables
+
+#endif  // ABSL_BASE_INTERNAL_INLINE_VARIABLE_EMULATION_H_
--- a/include/absl/base/internal/inline_variable_testing.h
+++ b/include/absl/base/internal/inline_variable_testing.h
@ -0,0 +1,46 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef ABSL_BASE_INLINE_VARIABLE_TESTING_H_
+#define ABSL_BASE_INLINE_VARIABLE_TESTING_H_
+
+#include "absl/base/internal/inline_variable.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace inline_variable_testing_internal {
+
+struct Foo {
+  int value = 5;
+};
+
+ABSL_INTERNAL_INLINE_CONSTEXPR(Foo, inline_variable_foo, {});
+ABSL_INTERNAL_INLINE_CONSTEXPR(Foo, other_inline_variable_foo, {});
+
+ABSL_INTERNAL_INLINE_CONSTEXPR(int, inline_variable_int, 5);
+ABSL_INTERNAL_INLINE_CONSTEXPR(int, other_inline_variable_int, 5);
+
+ABSL_INTERNAL_INLINE_CONSTEXPR(void(*)(), inline_variable_fun_ptr, nullptr);
+
+const Foo& get_foo_a();
+const Foo& get_foo_b();
+
+const int& get_int_a();
+const int& get_int_b();
+
+}  // namespace inline_variable_testing_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_BASE_INLINE_VARIABLE_TESTING_H_
--- a/include/absl/base/internal/invoke.h
+++ b/include/absl/base/internal/invoke.h
@ -0,0 +1,241 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// absl::base_internal::invoke(f, args...) is an implementation of
+// INVOKE(f, args...) from section [func.require] of the C++ standard.
+// When compiled as C++17 and later versions, it is implemented as an alias of
+// std::invoke.
+//
+// [func.require]
+// Define INVOKE (f, t1, t2, ..., tN) as follows:
+// 1. (t1.*f)(t2, ..., tN) when f is a pointer to a member function of a class T
+//    and t1 is an object of type T or a reference to an object of type T or a
+//    reference to an object of a type derived from T;
+// 2. ((*t1).*f)(t2, ..., tN) when f is a pointer to a member function of a
+//    class T and t1 is not one of the types described in the previous item;
+// 3. t1.*f when N == 1 and f is a pointer to member data of a class T and t1 is
+//    an object of type T or a reference to an object of type T or a reference
+//    to an object of a type derived from T;
+// 4. (*t1).*f when N == 1 and f is a pointer to member data of a class T and t1
+//    is not one of the types described in the previous item;
+// 5. f(t1, t2, ..., tN) in all other cases.
+//
+// The implementation is SFINAE-friendly: substitution failure within invoke()
+// isn't an error.
+
+#ifndef ABSL_BASE_INTERNAL_INVOKE_H_
+#define ABSL_BASE_INTERNAL_INVOKE_H_
+
+#include "absl/base/config.h"
+
+#if ABSL_INTERNAL_CPLUSPLUS_LANG >= 201703L
+
+#include <functional>
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace base_internal {
+
+using std::invoke;
+using std::invoke_result_t;
+using std::is_invocable_r;
+
+}  // namespace base_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#else  // ABSL_INTERNAL_CPLUSPLUS_LANG >= 201703L
+
+#include <algorithm>
+#include <type_traits>
+#include <utility>
+
+#include "absl/meta/type_traits.h"
+
+// The following code is internal implementation detail.  See the comment at the
+// top of this file for the API documentation.
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace base_internal {
+
+// The five classes below each implement one of the clauses from the definition
+// of INVOKE. The inner class template Accept<F, Args...> checks whether the
+// clause is applicable; static function template Invoke(f, args...) does the
+// invocation.
+//
+// By separating the clause selection logic from invocation we make sure that
+// Invoke() does exactly what the standard says.
+
+template <typename Derived>
+struct StrippedAccept {
+  template <typename... Args>
+  struct Accept : Derived::template AcceptImpl<typename std::remove_cv<
+                      typename std::remove_reference<Args>::type>::type...> {};
+};
+
+// (t1.*f)(t2, ..., tN) when f is a pointer to a member function of a class T
+// and t1 is an object of type T or a reference to an object of type T or a
+// reference to an object of a type derived from T.
+struct MemFunAndRef : StrippedAccept<MemFunAndRef> {
+  template <typename... Args>
+  struct AcceptImpl : std::false_type {};
+
+  template <typename MemFunType, typename C, typename Obj, typename... Args>
+  struct AcceptImpl<MemFunType C::*, Obj, Args...>
+      : std::integral_constant<bool, std::is_base_of<C, Obj>::value &&
+                                         absl::is_function<MemFunType>::value> {
+  };
+
+  template <typename MemFun, typename Obj, typename... Args>
+  static decltype((std::declval<Obj>().*
+                   std::declval<MemFun>())(std::declval<Args>()...))
+  Invoke(MemFun&& mem_fun, Obj&& obj, Args&&... args) {
+// Ignore bogus GCC warnings on this line.
+// See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101436 for similar example.
+#if ABSL_INTERNAL_HAVE_MIN_GNUC_VERSION(11, 0)
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Warray-bounds"
+#pragma GCC diagnostic ignored "-Wmaybe-uninitialized"
+#endif
+    return (std::forward<Obj>(obj).*
+            std::forward<MemFun>(mem_fun))(std::forward<Args>(args)...);
+#if ABSL_INTERNAL_HAVE_MIN_GNUC_VERSION(11, 0)
+#pragma GCC diagnostic pop
+#endif
+  }
+};
+
+// ((*t1).*f)(t2, ..., tN) when f is a pointer to a member function of a
+// class T and t1 is not one of the types described in the previous item.
+struct MemFunAndPtr : StrippedAccept<MemFunAndPtr> {
+  template <typename... Args>
+  struct AcceptImpl : std::false_type {};
+
+  template <typename MemFunType, typename C, typename Ptr, typename... Args>
+  struct AcceptImpl<MemFunType C::*, Ptr, Args...>
+      : std::integral_constant<bool, !std::is_base_of<C, Ptr>::value &&
+                                         absl::is_function<MemFunType>::value> {
+  };
+
+  template <typename MemFun, typename Ptr, typename... Args>
+  static decltype(((*std::declval<Ptr>()).*
+                   std::declval<MemFun>())(std::declval<Args>()...))
+  Invoke(MemFun&& mem_fun, Ptr&& ptr, Args&&... args) {
+    return ((*std::forward<Ptr>(ptr)).*
+            std::forward<MemFun>(mem_fun))(std::forward<Args>(args)...);
+  }
+};
+
+// t1.*f when N == 1 and f is a pointer to member data of a class T and t1 is
+// an object of type T or a reference to an object of type T or a reference
+// to an object of a type derived from T.
+struct DataMemAndRef : StrippedAccept<DataMemAndRef> {
+  template <typename... Args>
+  struct AcceptImpl : std::false_type {};
+
+  template <typename R, typename C, typename Obj>
+  struct AcceptImpl<R C::*, Obj>
+      : std::integral_constant<bool, std::is_base_of<C, Obj>::value &&
+                                         !absl::is_function<R>::value> {};
+
+  template <typename DataMem, typename Ref>
+  static decltype(std::declval<Ref>().*std::declval<DataMem>()) Invoke(
+      DataMem&& data_mem, Ref&& ref) {
+    return std::forward<Ref>(ref).*std::forward<DataMem>(data_mem);
+  }
+};
+
+// (*t1).*f when N == 1 and f is a pointer to member data of a class T and t1
+// is not one of the types described in the previous item.
+struct DataMemAndPtr : StrippedAccept<DataMemAndPtr> {
+  template <typename... Args>
+  struct AcceptImpl : std::false_type {};
+
+  template <typename R, typename C, typename Ptr>
+  struct AcceptImpl<R C::*, Ptr>
+      : std::integral_constant<bool, !std::is_base_of<C, Ptr>::value &&
+                                         !absl::is_function<R>::value> {};
+
+  template <typename DataMem, typename Ptr>
+  static decltype((*std::declval<Ptr>()).*std::declval<DataMem>()) Invoke(
+      DataMem&& data_mem, Ptr&& ptr) {
+    return (*std::forward<Ptr>(ptr)).*std::forward<DataMem>(data_mem);
+  }
+};
+
+// f(t1, t2, ..., tN) in all other cases.
+struct Callable {
+  // Callable doesn't have Accept because it's the last clause that gets picked
+  // when none of the previous clauses are applicable.
+  template <typename F, typename... Args>
+  static decltype(std::declval<F>()(std::declval<Args>()...)) Invoke(
+      F&& f, Args&&... args) {
+    return std::forward<F>(f)(std::forward<Args>(args)...);
+  }
+};
+
+// Resolves to the first matching clause.
+template <typename... Args>
+struct Invoker {
+  typedef typename std::conditional<
+      MemFunAndRef::Accept<Args...>::value, MemFunAndRef,
+      typename std::conditional<
+          MemFunAndPtr::Accept<Args...>::value, MemFunAndPtr,
+          typename std::conditional<
+              DataMemAndRef::Accept<Args...>::value, DataMemAndRef,
+              typename std::conditional<DataMemAndPtr::Accept<Args...>::value,
+                                        DataMemAndPtr, Callable>::type>::type>::
+          type>::type type;
+};
+
+// The result type of Invoke<F, Args...>.
+template <typename F, typename... Args>
+using invoke_result_t = decltype(Invoker<F, Args...>::type::Invoke(
+    std::declval<F>(), std::declval<Args>()...));
+
+// Invoke(f, args...) is an implementation of INVOKE(f, args...) from section
+// [func.require] of the C++ standard.
+template <typename F, typename... Args>
+invoke_result_t<F, Args...> invoke(F&& f, Args&&... args) {
+  return Invoker<F, Args...>::type::Invoke(std::forward<F>(f),
+                                           std::forward<Args>(args)...);
+}
+
+template <typename AlwaysVoid, typename, typename, typename...>
+struct IsInvocableRImpl : std::false_type {};
+
+template <typename R, typename F, typename... Args>
+struct IsInvocableRImpl<
+    absl::void_t<absl::base_internal::invoke_result_t<F, Args...> >, R, F,
+    Args...>
+    : std::integral_constant<
+          bool,
+          std::is_convertible<absl::base_internal::invoke_result_t<F, Args...>,
+                              R>::value ||
+              std::is_void<R>::value> {};
+
+// Type trait whose member `value` is true if invoking `F` with `Args` is valid,
+// and either the return type is convertible to `R`, or `R` is void.
+// C++11-compatible version of `std::is_invocable_r`.
+template <typename R, typename F, typename... Args>
+using is_invocable_r = IsInvocableRImpl<void, R, F, Args...>;
+
+}  // namespace base_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_INTERNAL_CPLUSPLUS_LANG >= 201703L
+
+#endif  // ABSL_BASE_INTERNAL_INVOKE_H_
--- a/include/absl/base/internal/low_level_alloc.h
+++ b/include/absl/base/internal/low_level_alloc.h
@ -0,0 +1,126 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+#ifndef ABSL_BASE_INTERNAL_LOW_LEVEL_ALLOC_H_
+#define ABSL_BASE_INTERNAL_LOW_LEVEL_ALLOC_H_
+
+// A simple thread-safe memory allocator that does not depend on
+// mutexes or thread-specific data.  It is intended to be used
+// sparingly, and only when malloc() would introduce an unwanted
+// dependency, such as inside the heap-checker, or the Mutex
+// implementation.
+
+// IWYU pragma: private, include "base/low_level_alloc.h"
+
+#include <sys/types.h>
+
+#include <cstdint>
+
+#include "absl/base/attributes.h"
+#include "absl/base/config.h"
+
+// LowLevelAlloc requires that the platform support low-level
+// allocation of virtual memory. Platforms lacking this cannot use
+// LowLevelAlloc.
+#ifdef ABSL_LOW_LEVEL_ALLOC_MISSING
+#error ABSL_LOW_LEVEL_ALLOC_MISSING cannot be directly set
+#elif !defined(ABSL_HAVE_MMAP) && !defined(_WIN32)
+#define ABSL_LOW_LEVEL_ALLOC_MISSING 1
+#endif
+
+// Using LowLevelAlloc with kAsyncSignalSafe isn't supported on Windows or
+// asm.js / WebAssembly.
+// See https://kripken.github.io/emscripten-site/docs/porting/pthreads.html
+// for more information.
+#ifdef ABSL_LOW_LEVEL_ALLOC_ASYNC_SIGNAL_SAFE_MISSING
+#error ABSL_LOW_LEVEL_ALLOC_ASYNC_SIGNAL_SAFE_MISSING cannot be directly set
+#elif defined(_WIN32) || defined(__asmjs__) || defined(__wasm__)
+#define ABSL_LOW_LEVEL_ALLOC_ASYNC_SIGNAL_SAFE_MISSING 1
+#endif
+
+#include <cstddef>
+
+#include "absl/base/port.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace base_internal {
+
+class LowLevelAlloc {
+ public:
+  struct Arena;       // an arena from which memory may be allocated
+
+  // Returns a pointer to a block of at least "request" bytes
+  // that have been newly allocated from the specific arena.
+  // for Alloc() call the DefaultArena() is used.
+  // Returns 0 if passed request==0.
+  // Does not return 0 under other circumstances; it crashes if memory
+  // is not available.
+  static void *Alloc(size_t request) ABSL_ATTRIBUTE_SECTION(malloc_hook);
+  static void *AllocWithArena(size_t request, Arena *arena)
+      ABSL_ATTRIBUTE_SECTION(malloc_hook);
+
+  // Deallocates a region of memory that was previously allocated with
+  // Alloc().   Does nothing if passed 0.   "s" must be either 0,
+  // or must have been returned from a call to Alloc() and not yet passed to
+  // Free() since that call to Alloc().  The space is returned to the arena
+  // from which it was allocated.
+  static void Free(void *s) ABSL_ATTRIBUTE_SECTION(malloc_hook);
+
+  // ABSL_ATTRIBUTE_SECTION(malloc_hook) for Alloc* and Free
+  // are to put all callers of MallocHook::Invoke* in this module
+  // into special section,
+  // so that MallocHook::GetCallerStackTrace can function accurately.
+
+  // Create a new arena.
+  // The root metadata for the new arena is allocated in the
+  // meta_data_arena; the DefaultArena() can be passed for meta_data_arena.
+  // These values may be ored into flags:
+  enum {
+    // Report calls to Alloc() and Free() via the MallocHook interface.
+    // Set in the DefaultArena.
+    kCallMallocHook = 0x0001,
+
+#ifndef ABSL_LOW_LEVEL_ALLOC_ASYNC_SIGNAL_SAFE_MISSING
+    // Make calls to Alloc(), Free() be async-signal-safe. Not set in
+    // DefaultArena(). Not supported on all platforms.
+    kAsyncSignalSafe = 0x0002,
+#endif
+  };
+  // Construct a new arena.  The allocation of the underlying metadata honors
+  // the provided flags.  For example, the call NewArena(kAsyncSignalSafe)
+  // is itself async-signal-safe, as well as generatating an arena that provides
+  // async-signal-safe Alloc/Free.
+  static Arena *NewArena(int32_t flags);
+
+  // Destroys an arena allocated by NewArena and returns true,
+  // provided no allocated blocks remain in the arena.
+  // If allocated blocks remain in the arena, does nothing and
+  // returns false.
+  // It is illegal to attempt to destroy the DefaultArena().
+  static bool DeleteArena(Arena *arena);
+
+  // The default arena that always exists.
+  static Arena *DefaultArena();
+
+ private:
+  LowLevelAlloc();      // no instances
+};
+
+}  // namespace base_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_BASE_INTERNAL_LOW_LEVEL_ALLOC_H_
--- a/include/absl/base/internal/low_level_scheduling.h
+++ b/include/absl/base/internal/low_level_scheduling.h
@ -0,0 +1,134 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// Core interfaces and definitions used by by low-level interfaces such as
+// SpinLock.
+
+#ifndef ABSL_BASE_INTERNAL_LOW_LEVEL_SCHEDULING_H_
+#define ABSL_BASE_INTERNAL_LOW_LEVEL_SCHEDULING_H_
+
+#include "absl/base/internal/raw_logging.h"
+#include "absl/base/internal/scheduling_mode.h"
+#include "absl/base/macros.h"
+
+// The following two declarations exist so SchedulingGuard may friend them with
+// the appropriate language linkage.  These callbacks allow libc internals, such
+// as function level statics, to schedule cooperatively when locking.
+extern "C" bool __google_disable_rescheduling(void);
+extern "C" void __google_enable_rescheduling(bool disable_result);
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+class CondVar;
+class Mutex;
+
+namespace synchronization_internal {
+int MutexDelay(int32_t c, int mode);
+}  // namespace synchronization_internal
+
+namespace base_internal {
+
+class SchedulingHelper;  // To allow use of SchedulingGuard.
+class SpinLock;          // To allow use of SchedulingGuard.
+
+// SchedulingGuard
+// Provides guard semantics that may be used to disable cooperative rescheduling
+// of the calling thread within specific program blocks.  This is used to
+// protect resources (e.g. low-level SpinLocks or Domain code) that cooperative
+// scheduling depends on.
+//
+// Domain implementations capable of rescheduling in reaction to involuntary
+// kernel thread actions (e.g blocking due to a pagefault or syscall) must
+// guarantee that an annotated thread is not allowed to (cooperatively)
+// reschedule until the annotated region is complete.
+//
+// It is an error to attempt to use a cooperatively scheduled resource (e.g.
+// Mutex) within a rescheduling-disabled region.
+//
+// All methods are async-signal safe.
+class SchedulingGuard {
+ public:
+  // Returns true iff the calling thread may be cooperatively rescheduled.
+  static bool ReschedulingIsAllowed();
+  SchedulingGuard(const SchedulingGuard&) = delete;
+  SchedulingGuard& operator=(const SchedulingGuard&) = delete;
+
+ private:
+  // Disable cooperative rescheduling of the calling thread.  It may still
+  // initiate scheduling operations (e.g. wake-ups), however, it may not itself
+  // reschedule.  Nestable.  The returned result is opaque, clients should not
+  // attempt to interpret it.
+  // REQUIRES: Result must be passed to a pairing EnableScheduling().
+  static bool DisableRescheduling();
+
+  // Marks the end of a rescheduling disabled region, previously started by
+  // DisableRescheduling().
+  // REQUIRES: Pairs with innermost call (and result) of DisableRescheduling().
+  static void EnableRescheduling(bool disable_result);
+
+  // A scoped helper for {Disable, Enable}Rescheduling().
+  // REQUIRES: destructor must run in same thread as constructor.
+  struct ScopedDisable {
+    ScopedDisable() { disabled = SchedulingGuard::DisableRescheduling(); }
+    ~ScopedDisable() { SchedulingGuard::EnableRescheduling(disabled); }
+
+    bool disabled;
+  };
+
+  // A scoped helper to enable rescheduling temporarily.
+  // REQUIRES: destructor must run in same thread as constructor.
+  class ScopedEnable {
+   public:
+    ScopedEnable();
+    ~ScopedEnable();
+
+   private:
+    int scheduling_disabled_depth_;
+  };
+
+  // Access to SchedulingGuard is explicitly permitted.
+  friend class absl::CondVar;
+  friend class absl::Mutex;
+  friend class SchedulingHelper;
+  friend class SpinLock;
+  friend int absl::synchronization_internal::MutexDelay(int32_t c, int mode);
+};
+
+//------------------------------------------------------------------------------
+// End of public interfaces.
+//------------------------------------------------------------------------------
+
+inline bool SchedulingGuard::ReschedulingIsAllowed() {
+  return false;
+}
+
+inline bool SchedulingGuard::DisableRescheduling() {
+  return false;
+}
+
+inline void SchedulingGuard::EnableRescheduling(bool /* disable_result */) {
+  return;
+}
+
+inline SchedulingGuard::ScopedEnable::ScopedEnable()
+    : scheduling_disabled_depth_(0) {}
+inline SchedulingGuard::ScopedEnable::~ScopedEnable() {
+  ABSL_RAW_CHECK(scheduling_disabled_depth_ == 0, "disable unused warning");
+}
+
+}  // namespace base_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_BASE_INTERNAL_LOW_LEVEL_SCHEDULING_H_
--- a/include/absl/base/internal/per_thread_tls.h
+++ b/include/absl/base/internal/per_thread_tls.h
@ -0,0 +1,52 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef ABSL_BASE_INTERNAL_PER_THREAD_TLS_H_
+#define ABSL_BASE_INTERNAL_PER_THREAD_TLS_H_
+
+// This header defines two macros:
+//
+// If the platform supports thread-local storage:
+//
+// * ABSL_PER_THREAD_TLS_KEYWORD is the C keyword needed to declare a
+//   thread-local variable
+// * ABSL_PER_THREAD_TLS is 1
+//
+// Otherwise:
+//
+// * ABSL_PER_THREAD_TLS_KEYWORD is empty
+// * ABSL_PER_THREAD_TLS is 0
+//
+// Microsoft C supports thread-local storage.
+// GCC supports it if the appropriate version of glibc is available,
+// which the programmer can indicate by defining ABSL_HAVE_TLS
+
+#include "absl/base/port.h"  // For ABSL_HAVE_TLS
+
+#if defined(ABSL_PER_THREAD_TLS)
+#error ABSL_PER_THREAD_TLS cannot be directly set
+#elif defined(ABSL_PER_THREAD_TLS_KEYWORD)
+#error ABSL_PER_THREAD_TLS_KEYWORD cannot be directly set
+#elif defined(ABSL_HAVE_TLS)
+#define ABSL_PER_THREAD_TLS_KEYWORD __thread
+#define ABSL_PER_THREAD_TLS 1
+#elif defined(_MSC_VER)
+#define ABSL_PER_THREAD_TLS_KEYWORD __declspec(thread)
+#define ABSL_PER_THREAD_TLS 1
+#else
+#define ABSL_PER_THREAD_TLS_KEYWORD
+#define ABSL_PER_THREAD_TLS 0
+#endif
+
+#endif  // ABSL_BASE_INTERNAL_PER_THREAD_TLS_H_
--- a/include/absl/base/internal/prefetch.h
+++ b/include/absl/base/internal/prefetch.h
@ -0,0 +1,138 @@
+// Copyright 2022 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef ABSL_BASE_INTERNAL_PREFETCH_H_
+#define ABSL_BASE_INTERNAL_PREFETCH_H_
+
+#include "absl/base/config.h"
+
+#ifdef __SSE__
+#include <xmmintrin.h>
+#endif
+
+#if defined(_MSC_VER) && defined(ABSL_INTERNAL_HAVE_SSE)
+#include <intrin.h>
+#pragma intrinsic(_mm_prefetch)
+#endif
+
+// Compatibility wrappers around __builtin_prefetch, to prefetch data
+// for read if supported by the toolchain.
+
+// Move data into the cache before it is read, or "prefetch" it.
+//
+// The value of `addr` is the address of the memory to prefetch. If
+// the target and compiler support it, data prefetch instructions are
+// generated. If the prefetch is done some time before the memory is
+// read, it may be in the cache by the time the read occurs.
+//
+// The function names specify the temporal locality heuristic applied,
+// using the names of Intel prefetch instructions:
+//
+//   T0 - high degree of temporal locality; data should be left in as
+//        many levels of the cache possible
+//   T1 - moderate degree of temporal locality
+//   T2 - low degree of temporal locality
+//   Nta - no temporal locality, data need not be left in the cache
+//         after the read
+//
+// Incorrect or gratuitous use of these functions can degrade
+// performance, so use them only when representative benchmarks show
+// an improvement.
+//
+// Example usage:
+//
+//   absl::base_internal::PrefetchT0(addr);
+//
+// Currently, the different prefetch calls behave on some Intel
+// architectures as follows:
+//
+//                 SNB..SKL   SKX
+// PrefetchT0()   L1/L2/L3  L1/L2
+// PrefetchT1()      L2/L3     L2
+// PrefetchT2()      L2/L3     L2
+// PrefetchNta()  L1/--/L3  L1*
+//
+// * On SKX PrefetchNta() will bring the line into L1 but will evict
+//   from L3 cache. This might result in surprising behavior.
+//
+// SNB = Sandy Bridge, SKL = Skylake, SKX = Skylake Xeon.
+//
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace base_internal {
+
+void PrefetchT0(const void* addr);
+void PrefetchT1(const void* addr);
+void PrefetchT2(const void* addr);
+void PrefetchNta(const void* addr);
+
+// Implementation details follow.
+
+#if ABSL_HAVE_BUILTIN(__builtin_prefetch) || defined(__GNUC__)
+
+#define ABSL_INTERNAL_HAVE_PREFETCH 1
+
+// See __builtin_prefetch:
+// https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html.
+//
+// These functions speculatively load for read only. This is
+// safe for all currently supported platforms. However, prefetch for
+// store may have problems depending on the target platform.
+//
+inline void PrefetchT0(const void* addr) {
+  // Note: this uses prefetcht0 on Intel.
+  __builtin_prefetch(addr, 0, 3);
+}
+inline void PrefetchT1(const void* addr) {
+  // Note: this uses prefetcht1 on Intel.
+  __builtin_prefetch(addr, 0, 2);
+}
+inline void PrefetchT2(const void* addr) {
+  // Note: this uses prefetcht2 on Intel.
+  __builtin_prefetch(addr, 0, 1);
+}
+inline void PrefetchNta(const void* addr) {
+  // Note: this uses prefetchtnta on Intel.
+  __builtin_prefetch(addr, 0, 0);
+}
+
+#elif defined(ABSL_INTERNAL_HAVE_SSE)
+
+#define ABSL_INTERNAL_HAVE_PREFETCH 1
+
+inline void PrefetchT0(const void* addr) {
+  _mm_prefetch(reinterpret_cast<const char*>(addr), _MM_HINT_T0);
+}
+inline void PrefetchT1(const void* addr) {
+  _mm_prefetch(reinterpret_cast<const char*>(addr), _MM_HINT_T1);
+}
+inline void PrefetchT2(const void* addr) {
+  _mm_prefetch(reinterpret_cast<const char*>(addr), _MM_HINT_T2);
+}
+inline void PrefetchNta(const void* addr) {
+  _mm_prefetch(reinterpret_cast<const char*>(addr), _MM_HINT_NTA);
+}
+
+#else
+inline void PrefetchT0(const void*) {}
+inline void PrefetchT1(const void*) {}
+inline void PrefetchT2(const void*) {}
+inline void PrefetchNta(const void*) {}
+#endif
+
+}  // namespace base_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_BASE_INTERNAL_PREFETCH_H_
--- a/include/absl/base/internal/pretty_function.h
+++ b/include/absl/base/internal/pretty_function.h
@ -0,0 +1,33 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef ABSL_BASE_INTERNAL_PRETTY_FUNCTION_H_
+#define ABSL_BASE_INTERNAL_PRETTY_FUNCTION_H_
+
+// ABSL_PRETTY_FUNCTION
+//
+// In C++11, __func__ gives the undecorated name of the current function.  That
+// is, "main", not "int main()".  Various compilers give extra macros to get the
+// decorated function name, including return type and arguments, to
+// differentiate between overload sets.  ABSL_PRETTY_FUNCTION is a portable
+// version of these macros which forwards to the correct macro on each compiler.
+#if defined(_MSC_VER)
+#define ABSL_PRETTY_FUNCTION __FUNCSIG__
+#elif defined(__GNUC__)
+#define ABSL_PRETTY_FUNCTION __PRETTY_FUNCTION__
+#else
+#error "Unsupported compiler"
+#endif
+
+#endif  // ABSL_BASE_INTERNAL_PRETTY_FUNCTION_H_
--- a/include/absl/base/internal/raw_logging.h
+++ b/include/absl/base/internal/raw_logging.h
@ -0,0 +1,196 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// Thread-safe logging routines that do not allocate any memory or
+// acquire any locks, and can therefore be used by low-level memory
+// allocation, synchronization, and signal-handling code.
+
+#ifndef ABSL_BASE_INTERNAL_RAW_LOGGING_H_
+#define ABSL_BASE_INTERNAL_RAW_LOGGING_H_
+
+#include <string>
+
+#include "absl/base/attributes.h"
+#include "absl/base/config.h"
+#include "absl/base/internal/atomic_hook.h"
+#include "absl/base/log_severity.h"
+#include "absl/base/macros.h"
+#include "absl/base/optimization.h"
+#include "absl/base/port.h"
+
+// This is similar to LOG(severity) << format..., but
+// * it is to be used ONLY by low-level modules that can't use normal LOG()
+// * it is designed to be a low-level logger that does not allocate any
+//   memory and does not need any locks, hence:
+// * it logs straight and ONLY to STDERR w/o buffering
+// * it uses an explicit printf-format and arguments list
+// * it will silently chop off really long message strings
+// Usage example:
+//   ABSL_RAW_LOG(ERROR, "Failed foo with %i: %s", status, error);
+// This will print an almost standard log line like this to stderr only:
+//   E0821 211317 file.cc:123] RAW: Failed foo with 22: bad_file
+
+#define ABSL_RAW_LOG(severity, ...)                                            \
+  do {                                                                         \
+    constexpr const char* absl_raw_logging_internal_basename =                 \
+        ::absl::raw_logging_internal::Basename(__FILE__,                       \
+                                               sizeof(__FILE__) - 1);          \
+    ::absl::raw_logging_internal::RawLog(ABSL_RAW_LOGGING_INTERNAL_##severity, \
+                                         absl_raw_logging_internal_basename,   \
+                                         __LINE__, __VA_ARGS__);               \
+  } while (0)
+
+// Similar to CHECK(condition) << message, but for low-level modules:
+// we use only ABSL_RAW_LOG that does not allocate memory.
+// We do not want to provide args list here to encourage this usage:
+//   if (!cond)  ABSL_RAW_LOG(FATAL, "foo ...", hard_to_compute_args);
+// so that the args are not computed when not needed.
+#define ABSL_RAW_CHECK(condition, message)                             \
+  do {                                                                 \
+    if (ABSL_PREDICT_FALSE(!(condition))) {                            \
+      ABSL_RAW_LOG(FATAL, "Check %s failed: %s", #condition, message); \
+    }                                                                  \
+  } while (0)
+
+// ABSL_INTERNAL_LOG and ABSL_INTERNAL_CHECK work like the RAW variants above,
+// except that if the richer log library is linked into the binary, we dispatch
+// to that instead.  This is potentially useful for internal logging and
+// assertions, where we are using RAW_LOG neither for its async-signal-safety
+// nor for its non-allocating nature, but rather because raw logging has very
+// few other dependencies.
+//
+// The API is a subset of the above: each macro only takes two arguments.  Use
+// StrCat if you need to build a richer message.
+#define ABSL_INTERNAL_LOG(severity, message)                                 \
+  do {                                                                       \
+    constexpr const char* absl_raw_logging_internal_filename = __FILE__;     \
+    ::absl::raw_logging_internal::internal_log_function(                     \
+        ABSL_RAW_LOGGING_INTERNAL_##severity,                                \
+        absl_raw_logging_internal_filename, __LINE__, message);              \
+    if (ABSL_RAW_LOGGING_INTERNAL_##severity == ::absl::LogSeverity::kFatal) \
+      ABSL_INTERNAL_UNREACHABLE;                                             \
+  } while (0)
+
+#define ABSL_INTERNAL_CHECK(condition, message)                    \
+  do {                                                             \
+    if (ABSL_PREDICT_FALSE(!(condition))) {                        \
+      std::string death_message = "Check " #condition " failed: "; \
+      death_message += std::string(message);                       \
+      ABSL_INTERNAL_LOG(FATAL, death_message);                     \
+    }                                                              \
+  } while (0)
+
+#define ABSL_RAW_LOGGING_INTERNAL_INFO ::absl::LogSeverity::kInfo
+#define ABSL_RAW_LOGGING_INTERNAL_WARNING ::absl::LogSeverity::kWarning
+#define ABSL_RAW_LOGGING_INTERNAL_ERROR ::absl::LogSeverity::kError
+#define ABSL_RAW_LOGGING_INTERNAL_FATAL ::absl::LogSeverity::kFatal
+#define ABSL_RAW_LOGGING_INTERNAL_LEVEL(severity) \
+  ::absl::NormalizeLogSeverity(severity)
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace raw_logging_internal {
+
+// Helper function to implement ABSL_RAW_LOG
+// Logs format... at "severity" level, reporting it
+// as called from file:line.
+// This does not allocate memory or acquire locks.
+void RawLog(absl::LogSeverity severity, const char* file, int line,
+            const char* format, ...) ABSL_PRINTF_ATTRIBUTE(4, 5);
+
+// Writes the provided buffer directly to stderr, in a signal-safe, low-level
+// manner.
+void AsyncSignalSafeWriteToStderr(const char* s, size_t len);
+
+// compile-time function to get the "base" filename, that is, the part of
+// a filename after the last "/" or "\" path separator.  The search starts at
+// the end of the string; the second parameter is the length of the string.
+constexpr const char* Basename(const char* fname, int offset) {
+  return offset == 0 || fname[offset - 1] == '/' || fname[offset - 1] == '\\'
+             ? fname + offset
+             : Basename(fname, offset - 1);
+}
+
+// For testing only.
+// Returns true if raw logging is fully supported. When it is not
+// fully supported, no messages will be emitted, but a log at FATAL
+// severity will cause an abort.
+//
+// TODO(gfalcon): Come up with a better name for this method.
+bool RawLoggingFullySupported();
+
+// Function type for a raw_logging customization hook for suppressing messages
+// by severity, and for writing custom prefixes on non-suppressed messages.
+//
+// The installed hook is called for every raw log invocation.  The message will
+// be logged to stderr only if the hook returns true.  FATAL errors will cause
+// the process to abort, even if writing to stderr is suppressed.  The hook is
+// also provided with an output buffer, where it can write a custom log message
+// prefix.
+//
+// The raw_logging system does not allocate memory or grab locks.  User-provided
+// hooks must avoid these operations, and must not throw exceptions.
+//
+// 'severity' is the severity level of the message being written.
+// 'file' and 'line' are the file and line number where the ABSL_RAW_LOG macro
+// was located.
+// 'buf' and 'buf_size' are pointers to the buffer and buffer size.  If the
+// hook writes a prefix, it must increment *buf and decrement *buf_size
+// accordingly.
+using LogFilterAndPrefixHook = bool (*)(absl::LogSeverity severity,
+                                        const char* file, int line, char** buf,
+                                        int* buf_size);
+
+// Function type for a raw_logging customization hook called to abort a process
+// when a FATAL message is logged.  If the provided AbortHook() returns, the
+// logging system will call abort().
+//
+// 'file' and 'line' are the file and line number where the ABSL_RAW_LOG macro
+// was located.
+// The NUL-terminated logged message lives in the buffer between 'buf_start'
+// and 'buf_end'.  'prefix_end' points to the first non-prefix character of the
+// buffer (as written by the LogFilterAndPrefixHook.)
+//
+// The lifetime of the filename and message buffers will not end while the
+// process remains alive.
+using AbortHook = void (*)(const char* file, int line, const char* buf_start,
+                           const char* prefix_end, const char* buf_end);
+
+// Internal logging function for ABSL_INTERNAL_LOG to dispatch to.
+//
+// TODO(gfalcon): When string_view no longer depends on base, change this
+// interface to take its message as a string_view instead.
+using InternalLogFunction = void (*)(absl::LogSeverity severity,
+                                     const char* file, int line,
+                                     const std::string& message);
+
+ABSL_INTERNAL_ATOMIC_HOOK_ATTRIBUTES ABSL_DLL extern base_internal::AtomicHook<
+    InternalLogFunction>
+    internal_log_function;
+
+// Registers hooks of the above types.  Only a single hook of each type may be
+// registered.  It is an error to call these functions multiple times with
+// different input arguments.
+//
+// These functions are safe to call at any point during initialization; they do
+// not block or malloc, and are async-signal safe.
+void RegisterLogFilterAndPrefixHook(LogFilterAndPrefixHook func);
+void RegisterAbortHook(AbortHook func);
+void RegisterInternalLogFunction(InternalLogFunction func);
+
+}  // namespace raw_logging_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_BASE_INTERNAL_RAW_LOGGING_H_
--- a/include/absl/base/internal/scheduling_mode.h
+++ b/include/absl/base/internal/scheduling_mode.h
@ -0,0 +1,58 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// Core interfaces and definitions used by by low-level interfaces such as
+// SpinLock.
+
+#ifndef ABSL_BASE_INTERNAL_SCHEDULING_MODE_H_
+#define ABSL_BASE_INTERNAL_SCHEDULING_MODE_H_
+
+#include "absl/base/config.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace base_internal {
+
+// Used to describe how a thread may be scheduled.  Typically associated with
+// the declaration of a resource supporting synchronized access.
+//
+// SCHEDULE_COOPERATIVE_AND_KERNEL:
+// Specifies that when waiting, a cooperative thread (e.g. a Fiber) may
+// reschedule (using base::scheduling semantics); allowing other cooperative
+// threads to proceed.
+//
+// SCHEDULE_KERNEL_ONLY: (Also described as "non-cooperative")
+// Specifies that no cooperative scheduling semantics may be used, even if the
+// current thread is itself cooperatively scheduled.  This means that
+// cooperative threads will NOT allow other cooperative threads to execute in
+// their place while waiting for a resource of this type.  Host operating system
+// semantics (e.g. a futex) may still be used.
+//
+// When optional, clients should strongly prefer SCHEDULE_COOPERATIVE_AND_KERNEL
+// by default.  SCHEDULE_KERNEL_ONLY should only be used for resources on which
+// base::scheduling (e.g. the implementation of a Scheduler) may depend.
+//
+// NOTE: Cooperative resources may not be nested below non-cooperative ones.
+// This means that it is invalid to to acquire a SCHEDULE_COOPERATIVE_AND_KERNEL
+// resource if a SCHEDULE_KERNEL_ONLY resource is already held.
+enum SchedulingMode {
+  SCHEDULE_KERNEL_ONLY = 0,         // Allow scheduling only the host OS.
+  SCHEDULE_COOPERATIVE_AND_KERNEL,  // Also allow cooperative scheduling.
+};
+
+}  // namespace base_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_BASE_INTERNAL_SCHEDULING_MODE_H_
--- a/include/absl/base/internal/scoped_set_env.h
+++ b/include/absl/base/internal/scoped_set_env.h
@ -0,0 +1,45 @@
+//
+// Copyright 2019 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+#ifndef ABSL_BASE_INTERNAL_SCOPED_SET_ENV_H_
+#define ABSL_BASE_INTERNAL_SCOPED_SET_ENV_H_
+
+#include <string>
+
+#include "absl/base/config.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace base_internal {
+
+class ScopedSetEnv {
+ public:
+  ScopedSetEnv(const char* var_name, const char* new_value);
+  ~ScopedSetEnv();
+
+ private:
+  std::string var_name_;
+  std::string old_value_;
+
+  // True if the environment variable was initially not set.
+  bool was_unset_;
+};
+
+}  // namespace base_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_BASE_INTERNAL_SCOPED_SET_ENV_H_
--- a/include/absl/base/internal/spinlock.h
+++ b/include/absl/base/internal/spinlock.h
@ -0,0 +1,256 @@
+//
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+//  Most users requiring mutual exclusion should use Mutex.
+//  SpinLock is provided for use in two situations:
+//   - for use by Abseil internal code that Mutex itself depends on
+//   - for async signal safety (see below)
+
+// SpinLock is async signal safe.  If a spinlock is used within a signal
+// handler, all code that acquires the lock must ensure that the signal cannot
+// arrive while they are holding the lock.  Typically, this is done by blocking
+// the signal.
+//
+// Threads waiting on a SpinLock may be woken in an arbitrary order.
+
+#ifndef ABSL_BASE_INTERNAL_SPINLOCK_H_
+#define ABSL_BASE_INTERNAL_SPINLOCK_H_
+
+#include <stdint.h>
+#include <sys/types.h>
+
+#include <atomic>
+
+#include "absl/base/attributes.h"
+#include "absl/base/const_init.h"
+#include "absl/base/dynamic_annotations.h"
+#include "absl/base/internal/low_level_scheduling.h"
+#include "absl/base/internal/raw_logging.h"
+#include "absl/base/internal/scheduling_mode.h"
+#include "absl/base/internal/tsan_mutex_interface.h"
+#include "absl/base/macros.h"
+#include "absl/base/port.h"
+#include "absl/base/thread_annotations.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace base_internal {
+
+class ABSL_LOCKABLE SpinLock {
+ public:
+  SpinLock() : lockword_(kSpinLockCooperative) {
+    ABSL_TSAN_MUTEX_CREATE(this, __tsan_mutex_not_static);
+  }
+
+  // Constructors that allow non-cooperative spinlocks to be created for use
+  // inside thread schedulers.  Normal clients should not use these.
+  explicit SpinLock(base_internal::SchedulingMode mode);
+
+  // Constructor for global SpinLock instances.  See absl/base/const_init.h.
+  constexpr SpinLock(absl::ConstInitType, base_internal::SchedulingMode mode)
+      : lockword_(IsCooperative(mode) ? kSpinLockCooperative : 0) {}
+
+  // For global SpinLock instances prefer trivial destructor when possible.
+  // Default but non-trivial destructor in some build configurations causes an
+  // extra static initializer.
+#ifdef ABSL_INTERNAL_HAVE_TSAN_INTERFACE
+  ~SpinLock() { ABSL_TSAN_MUTEX_DESTROY(this, __tsan_mutex_not_static); }
+#else
+  ~SpinLock() = default;
+#endif
+
+  // Acquire this SpinLock.
+  inline void Lock() ABSL_EXCLUSIVE_LOCK_FUNCTION() {
+    ABSL_TSAN_MUTEX_PRE_LOCK(this, 0);
+    if (!TryLockImpl()) {
+      SlowLock();
+    }
+    ABSL_TSAN_MUTEX_POST_LOCK(this, 0, 0);
+  }
+
+  // Try to acquire this SpinLock without blocking and return true if the
+  // acquisition was successful.  If the lock was not acquired, false is
+  // returned.  If this SpinLock is free at the time of the call, TryLock
+  // will return true with high probability.
+  inline bool TryLock() ABSL_EXCLUSIVE_TRYLOCK_FUNCTION(true) {
+    ABSL_TSAN_MUTEX_PRE_LOCK(this, __tsan_mutex_try_lock);
+    bool res = TryLockImpl();
+    ABSL_TSAN_MUTEX_POST_LOCK(
+        this, __tsan_mutex_try_lock | (res ? 0 : __tsan_mutex_try_lock_failed),
+        0);
+    return res;
+  }
+
+  // Release this SpinLock, which must be held by the calling thread.
+  inline void Unlock() ABSL_UNLOCK_FUNCTION() {
+    ABSL_TSAN_MUTEX_PRE_UNLOCK(this, 0);
+    uint32_t lock_value = lockword_.load(std::memory_order_relaxed);
+    lock_value = lockword_.exchange(lock_value & kSpinLockCooperative,
+                                    std::memory_order_release);
+
+    if ((lock_value & kSpinLockDisabledScheduling) != 0) {
+      base_internal::SchedulingGuard::EnableRescheduling(true);
+    }
+    if ((lock_value & kWaitTimeMask) != 0) {
+      // Collect contentionz profile info, and speed the wakeup of any waiter.
+      // The wait_cycles value indicates how long this thread spent waiting
+      // for the lock.
+      SlowUnlock(lock_value);
+    }
+    ABSL_TSAN_MUTEX_POST_UNLOCK(this, 0);
+  }
+
+  // Determine if the lock is held.  When the lock is held by the invoking
+  // thread, true will always be returned. Intended to be used as
+  // CHECK(lock.IsHeld()).
+  inline bool IsHeld() const {
+    return (lockword_.load(std::memory_order_relaxed) & kSpinLockHeld) != 0;
+  }
+
+  // Return immediately if this thread holds the SpinLock exclusively.
+  // Otherwise, report an error by crashing with a diagnostic.
+  inline void AssertHeld() const ABSL_ASSERT_EXCLUSIVE_LOCK() {
+    if (!IsHeld()) {
+      ABSL_RAW_LOG(FATAL, "thread should hold the lock on SpinLock");
+    }
+  }
+
+ protected:
+  // These should not be exported except for testing.
+
+  // Store number of cycles between wait_start_time and wait_end_time in a
+  // lock value.
+  static uint32_t EncodeWaitCycles(int64_t wait_start_time,
+                                   int64_t wait_end_time);
+
+  // Extract number of wait cycles in a lock value.
+  static uint64_t DecodeWaitCycles(uint32_t lock_value);
+
+  // Provide access to protected method above.  Use for testing only.
+  friend struct SpinLockTest;
+
+ private:
+  // lockword_ is used to store the following:
+  //
+  // bit[0] encodes whether a lock is being held.
+  // bit[1] encodes whether a lock uses cooperative scheduling.
+  // bit[2] encodes whether the current lock holder disabled scheduling when
+  //        acquiring the lock. Only set when kSpinLockHeld is also set.
+  // bit[3:31] encodes time a lock spent on waiting as a 29-bit unsigned int.
+  //        This is set by the lock holder to indicate how long it waited on
+  //        the lock before eventually acquiring it. The number of cycles is
+  //        encoded as a 29-bit unsigned int, or in the case that the current
+  //        holder did not wait but another waiter is queued, the LSB
+  //        (kSpinLockSleeper) is set. The implementation does not explicitly
+  //        track the number of queued waiters beyond this. It must always be
+  //        assumed that waiters may exist if the current holder was required to
+  //        queue.
+  //
+  // Invariant: if the lock is not held, the value is either 0 or
+  // kSpinLockCooperative.
+  static constexpr uint32_t kSpinLockHeld = 1;
+  static constexpr uint32_t kSpinLockCooperative = 2;
+  static constexpr uint32_t kSpinLockDisabledScheduling = 4;
+  static constexpr uint32_t kSpinLockSleeper = 8;
+  // Includes kSpinLockSleeper.
+  static constexpr uint32_t kWaitTimeMask =
+      ~(kSpinLockHeld | kSpinLockCooperative | kSpinLockDisabledScheduling);
+
+  // Returns true if the provided scheduling mode is cooperative.
+  static constexpr bool IsCooperative(
+      base_internal::SchedulingMode scheduling_mode) {
+    return scheduling_mode == base_internal::SCHEDULE_COOPERATIVE_AND_KERNEL;
+  }
+
+  uint32_t TryLockInternal(uint32_t lock_value, uint32_t wait_cycles);
+  void SlowLock() ABSL_ATTRIBUTE_COLD;
+  void SlowUnlock(uint32_t lock_value) ABSL_ATTRIBUTE_COLD;
+  uint32_t SpinLoop();
+
+  inline bool TryLockImpl() {
+    uint32_t lock_value = lockword_.load(std::memory_order_relaxed);
+    return (TryLockInternal(lock_value, 0) & kSpinLockHeld) == 0;
+  }
+
+  std::atomic<uint32_t> lockword_;
+
+  SpinLock(const SpinLock&) = delete;
+  SpinLock& operator=(const SpinLock&) = delete;
+};
+
+// Corresponding locker object that arranges to acquire a spinlock for
+// the duration of a C++ scope.
+class ABSL_SCOPED_LOCKABLE SpinLockHolder {
+ public:
+  inline explicit SpinLockHolder(SpinLock* l) ABSL_EXCLUSIVE_LOCK_FUNCTION(l)
+      : lock_(l) {
+    l->Lock();
+  }
+  inline ~SpinLockHolder() ABSL_UNLOCK_FUNCTION() { lock_->Unlock(); }
+
+  SpinLockHolder(const SpinLockHolder&) = delete;
+  SpinLockHolder& operator=(const SpinLockHolder&) = delete;
+
+ private:
+  SpinLock* lock_;
+};
+
+// Register a hook for profiling support.
+//
+// The function pointer registered here will be called whenever a spinlock is
+// contended.  The callback is given an opaque handle to the contended spinlock
+// and the number of wait cycles.  This is thread-safe, but only a single
+// profiler can be registered.  It is an error to call this function multiple
+// times with different arguments.
+void RegisterSpinLockProfiler(void (*fn)(const void* lock,
+                                         int64_t wait_cycles));
+
+//------------------------------------------------------------------------------
+// Public interface ends here.
+//------------------------------------------------------------------------------
+
+// If (result & kSpinLockHeld) == 0, then *this was successfully locked.
+// Otherwise, returns last observed value for lockword_.
+inline uint32_t SpinLock::TryLockInternal(uint32_t lock_value,
+                                          uint32_t wait_cycles) {
+  if ((lock_value & kSpinLockHeld) != 0) {
+    return lock_value;
+  }
+
+  uint32_t sched_disabled_bit = 0;
+  if ((lock_value & kSpinLockCooperative) == 0) {
+    // For non-cooperative locks we must make sure we mark ourselves as
+    // non-reschedulable before we attempt to CompareAndSwap.
+    if (base_internal::SchedulingGuard::DisableRescheduling()) {
+      sched_disabled_bit = kSpinLockDisabledScheduling;
+    }
+  }
+
+  if (!lockword_.compare_exchange_strong(
+          lock_value,
+          kSpinLockHeld | lock_value | wait_cycles | sched_disabled_bit,
+          std::memory_order_acquire, std::memory_order_relaxed)) {
+    base_internal::SchedulingGuard::EnableRescheduling(sched_disabled_bit != 0);
+  }
+
+  return lock_value;
+}
+
+}  // namespace base_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_BASE_INTERNAL_SPINLOCK_H_
--- a/include/absl/base/internal/spinlock_akaros.inc
+++ b/include/absl/base/internal/spinlock_akaros.inc
@ -0,0 +1,35 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// This file is an Akaros-specific part of spinlock_wait.cc
+
+#include <atomic>
+
+#include "absl/base/internal/scheduling_mode.h"
+
+extern "C" {
+
+ABSL_ATTRIBUTE_WEAK void ABSL_INTERNAL_C_SYMBOL(AbslInternalSpinLockDelay)(
+    std::atomic<uint32_t>* /* lock_word */, uint32_t /* value */,
+    int /* loop */, absl::base_internal::SchedulingMode /* mode */) {
+  // In Akaros, one must take care not to call anything that could cause a
+  // malloc(), a blocking system call, or a uthread_yield() while holding a
+  // spinlock. Our callers assume will not call into libraries or other
+  // arbitrary code.
+}
+
+ABSL_ATTRIBUTE_WEAK void ABSL_INTERNAL_C_SYMBOL(AbslInternalSpinLockWake)(
+    std::atomic<uint32_t>* /* lock_word */, bool /* all */) {}
+
+}  // extern "C"
--- a/include/absl/base/internal/spinlock_linux.inc
+++ b/include/absl/base/internal/spinlock_linux.inc
@ -0,0 +1,71 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// This file is a Linux-specific part of spinlock_wait.cc
+
+#include <linux/futex.h>
+#include <sys/syscall.h>
+#include <unistd.h>
+
+#include <atomic>
+#include <climits>
+#include <cstdint>
+#include <ctime>
+
+#include "absl/base/attributes.h"
+#include "absl/base/internal/errno_saver.h"
+
+// The SpinLock lockword is `std::atomic<uint32_t>`. Here we assert that
+// `std::atomic<uint32_t>` is bitwise equivalent of the `int` expected
+// by SYS_futex. We also assume that reads/writes done to the lockword
+// by SYS_futex have rational semantics with regard to the
+// std::atomic<> API. C++ provides no guarantees of these assumptions,
+// but they are believed to hold in practice.
+static_assert(sizeof(std::atomic<uint32_t>) == sizeof(int),
+              "SpinLock lockword has the wrong size for a futex");
+
+// Some Android headers are missing these definitions even though they
+// support these futex operations.
+#ifdef __BIONIC__
+#ifndef SYS_futex
+#define SYS_futex __NR_futex
+#endif
+#ifndef FUTEX_PRIVATE_FLAG
+#define FUTEX_PRIVATE_FLAG 128
+#endif
+#endif
+
+#if defined(__NR_futex_time64) && !defined(SYS_futex_time64)
+#define SYS_futex_time64 __NR_futex_time64
+#endif
+
+#if defined(SYS_futex_time64) && !defined(SYS_futex)
+#define SYS_futex SYS_futex_time64
+#endif
+
+extern "C" {
+
+ABSL_ATTRIBUTE_WEAK void ABSL_INTERNAL_C_SYMBOL(AbslInternalSpinLockDelay)(
+    std::atomic<uint32_t> *w, uint32_t value, int,
+    absl::base_internal::SchedulingMode) {
+  absl::base_internal::ErrnoSaver errno_saver;
+  syscall(SYS_futex, w, FUTEX_WAIT | FUTEX_PRIVATE_FLAG, value, nullptr);
+}
+
+ABSL_ATTRIBUTE_WEAK void ABSL_INTERNAL_C_SYMBOL(AbslInternalSpinLockWake)(
+    std::atomic<uint32_t> *w, bool all) {
+  syscall(SYS_futex, w, FUTEX_WAKE | FUTEX_PRIVATE_FLAG, all ? INT_MAX : 1, 0);
+}
+
+}  // extern "C"
--- a/include/absl/base/internal/spinlock_posix.inc
+++ b/include/absl/base/internal/spinlock_posix.inc
@ -0,0 +1,46 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// This file is a Posix-specific part of spinlock_wait.cc
+
+#include <sched.h>
+
+#include <atomic>
+#include <ctime>
+
+#include "absl/base/internal/errno_saver.h"
+#include "absl/base/internal/scheduling_mode.h"
+#include "absl/base/port.h"
+
+extern "C" {
+
+ABSL_ATTRIBUTE_WEAK void ABSL_INTERNAL_C_SYMBOL(AbslInternalSpinLockDelay)(
+    std::atomic<uint32_t>* /* lock_word */, uint32_t /* value */, int loop,
+    absl::base_internal::SchedulingMode /* mode */) {
+  absl::base_internal::ErrnoSaver errno_saver;
+  if (loop == 0) {
+  } else if (loop == 1) {
+    sched_yield();
+  } else {
+    struct timespec tm;
+    tm.tv_sec = 0;
+    tm.tv_nsec = absl::base_internal::SpinLockSuggestedDelayNS(loop);
+    nanosleep(&tm, nullptr);
+  }
+}
+
+ABSL_ATTRIBUTE_WEAK void ABSL_INTERNAL_C_SYMBOL(AbslInternalSpinLockWake)(
+    std::atomic<uint32_t>* /* lock_word */, bool /* all */) {}
+
+}  // extern "C"
--- a/include/absl/base/internal/spinlock_wait.h
+++ b/include/absl/base/internal/spinlock_wait.h
@ -0,0 +1,95 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef ABSL_BASE_INTERNAL_SPINLOCK_WAIT_H_
+#define ABSL_BASE_INTERNAL_SPINLOCK_WAIT_H_
+
+// Operations to make atomic transitions on a word, and to allow
+// waiting for those transitions to become possible.
+
+#include <stdint.h>
+#include <atomic>
+
+#include "absl/base/internal/scheduling_mode.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace base_internal {
+
+// SpinLockWait() waits until it can perform one of several transitions from
+// "from" to "to".  It returns when it performs a transition where done==true.
+struct SpinLockWaitTransition {
+  uint32_t from;
+  uint32_t to;
+  bool done;
+};
+
+// Wait until *w can transition from trans[i].from to trans[i].to for some i
+// satisfying 0<=i<n && trans[i].done, atomically make the transition,
+// then return the old value of *w.   Make any other atomic transitions
+// where !trans[i].done, but continue waiting.
+//
+// Wakeups for threads blocked on SpinLockWait do not respect priorities.
+uint32_t SpinLockWait(std::atomic<uint32_t> *w, int n,
+                      const SpinLockWaitTransition trans[],
+                      SchedulingMode scheduling_mode);
+
+// If possible, wake some thread that has called SpinLockDelay(w, ...). If `all`
+// is true, wake all such threads. On some systems, this may be a no-op; on
+// those systems, threads calling SpinLockDelay() will always wake eventually
+// even if SpinLockWake() is never called.
+void SpinLockWake(std::atomic<uint32_t> *w, bool all);
+
+// Wait for an appropriate spin delay on iteration "loop" of a
+// spin loop on location *w, whose previously observed value was "value".
+// SpinLockDelay() may do nothing, may yield the CPU, may sleep a clock tick,
+// or may wait for a call to SpinLockWake(w).
+void SpinLockDelay(std::atomic<uint32_t> *w, uint32_t value, int loop,
+                   base_internal::SchedulingMode scheduling_mode);
+
+// Helper used by AbslInternalSpinLockDelay.
+// Returns a suggested delay in nanoseconds for iteration number "loop".
+int SpinLockSuggestedDelayNS(int loop);
+
+}  // namespace base_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+// In some build configurations we pass --detect-odr-violations to the
+// gold linker.  This causes it to flag weak symbol overrides as ODR
+// violations.  Because ODR only applies to C++ and not C,
+// --detect-odr-violations ignores symbols not mangled with C++ names.
+// By changing our extension points to be extern "C", we dodge this
+// check.
+extern "C" {
+void ABSL_INTERNAL_C_SYMBOL(AbslInternalSpinLockWake)(std::atomic<uint32_t> *w,
+                                                      bool all);
+void ABSL_INTERNAL_C_SYMBOL(AbslInternalSpinLockDelay)(
+    std::atomic<uint32_t> *w, uint32_t value, int loop,
+    absl::base_internal::SchedulingMode scheduling_mode);
+}
+
+inline void absl::base_internal::SpinLockWake(std::atomic<uint32_t> *w,
+                                              bool all) {
+  ABSL_INTERNAL_C_SYMBOL(AbslInternalSpinLockWake)(w, all);
+}
+
+inline void absl::base_internal::SpinLockDelay(
+    std::atomic<uint32_t> *w, uint32_t value, int loop,
+    absl::base_internal::SchedulingMode scheduling_mode) {
+  ABSL_INTERNAL_C_SYMBOL(AbslInternalSpinLockDelay)
+  (w, value, loop, scheduling_mode);
+}
+
+#endif  // ABSL_BASE_INTERNAL_SPINLOCK_WAIT_H_
--- a/include/absl/base/internal/spinlock_win32.inc
+++ b/include/absl/base/internal/spinlock_win32.inc
@ -0,0 +1,37 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// This file is a Win32-specific part of spinlock_wait.cc
+
+#include <windows.h>
+#include <atomic>
+#include "absl/base/internal/scheduling_mode.h"
+
+extern "C" {
+
+void ABSL_INTERNAL_C_SYMBOL(AbslInternalSpinLockDelay)(
+    std::atomic<uint32_t>* /* lock_word */, uint32_t /* value */, int loop,
+    absl::base_internal::SchedulingMode /* mode */) {
+  if (loop == 0) {
+  } else if (loop == 1) {
+    Sleep(0);
+  } else {
+    Sleep(absl::base_internal::SpinLockSuggestedDelayNS(loop) / 1000000);
+  }
+}
+
+void ABSL_INTERNAL_C_SYMBOL(AbslInternalSpinLockWake)(
+    std::atomic<uint32_t>* /* lock_word */, bool /* all */) {}
+
+}  // extern "C"
--- a/include/absl/base/internal/strerror.h
+++ b/include/absl/base/internal/strerror.h
@ -0,0 +1,39 @@
+// Copyright 2020 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef ABSL_BASE_INTERNAL_STRERROR_H_
+#define ABSL_BASE_INTERNAL_STRERROR_H_
+
+#include <string>
+
+#include "absl/base/config.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace base_internal {
+
+// A portable and thread-safe alternative to C89's `strerror`.
+//
+// The C89 specification of `strerror` is not suitable for use in a
+// multi-threaded application as the returned string may be changed by calls to
+// `strerror` from another thread.  The many non-stdlib alternatives differ
+// enough in their names, availability, and semantics to justify this wrapper
+// around them.  `errno` will not be modified by a call to `absl::StrError`.
+std::string StrError(int errnum);
+
+}  // namespace base_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_BASE_INTERNAL_STRERROR_H_
--- a/include/absl/base/internal/sysinfo.h
+++ b/include/absl/base/internal/sysinfo.h
@ -0,0 +1,74 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// This file includes routines to find out characteristics
+// of the machine a program is running on.  It is undoubtedly
+// system-dependent.
+
+// Functions listed here that accept a pid_t as an argument act on the
+// current process if the pid_t argument is 0
+// All functions here are thread-hostile due to file caching unless
+// commented otherwise.
+
+#ifndef ABSL_BASE_INTERNAL_SYSINFO_H_
+#define ABSL_BASE_INTERNAL_SYSINFO_H_
+
+#ifndef _WIN32
+#include <sys/types.h>
+#endif
+
+#include <cstdint>
+
+#include "absl/base/config.h"
+#include "absl/base/port.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace base_internal {
+
+// Nominal core processor cycles per second of each processor.   This is _not_
+// necessarily the frequency of the CycleClock counter (see cycleclock.h)
+// Thread-safe.
+double NominalCPUFrequency();
+
+// Number of logical processors (hyperthreads) in system. Thread-safe.
+int NumCPUs();
+
+// Return the thread id of the current thread, as told by the system.
+// No two currently-live threads implemented by the OS shall have the same ID.
+// Thread ids of exited threads may be reused.   Multiple user-level threads
+// may have the same thread ID if multiplexed on the same OS thread.
+//
+// On Linux, you may send a signal to the resulting ID with kill().  However,
+// it is recommended for portability that you use pthread_kill() instead.
+#ifdef _WIN32
+// On Windows, process id and thread id are of the same type according to the
+// return types of GetProcessId() and GetThreadId() are both DWORD, an unsigned
+// 32-bit type.
+using pid_t = uint32_t;
+#endif
+pid_t GetTID();
+
+// Like GetTID(), but caches the result in thread-local storage in order
+// to avoid unnecessary system calls. Note that there are some cases where
+// one must call through to GetTID directly, which is why this exists as a
+// separate function. For example, GetCachedTID() is not safe to call in
+// an asynchronous signal-handling context nor right after a call to fork().
+pid_t GetCachedTID();
+
+}  // namespace base_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_BASE_INTERNAL_SYSINFO_H_
--- a/include/absl/base/internal/thread_annotations.h
+++ b/include/absl/base/internal/thread_annotations.h
@ -0,0 +1,271 @@
+// Copyright 2019 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// -----------------------------------------------------------------------------
+// File: thread_annotations.h
+// -----------------------------------------------------------------------------
+//
+// WARNING: This is a backwards compatible header and it will be removed after
+// the migration to prefixed thread annotations is finished; please include
+// "absl/base/thread_annotations.h".
+//
+// This header file contains macro definitions for thread safety annotations
+// that allow developers to document the locking policies of multi-threaded
+// code. The annotations can also help program analysis tools to identify
+// potential thread safety issues.
+//
+// These annotations are implemented using compiler attributes. Using the macros
+// defined here instead of raw attributes allow for portability and future
+// compatibility.
+//
+// When referring to mutexes in the arguments of the attributes, you should
+// use variable names or more complex expressions (e.g. my_object->mutex_)
+// that evaluate to a concrete mutex object whenever possible. If the mutex
+// you want to refer to is not in scope, you may use a member pointer
+// (e.g. &MyClass::mutex_) to refer to a mutex in some (unknown) object.
+
+#ifndef ABSL_BASE_INTERNAL_THREAD_ANNOTATIONS_H_
+#define ABSL_BASE_INTERNAL_THREAD_ANNOTATIONS_H_
+
+#if defined(__clang__)
+#define THREAD_ANNOTATION_ATTRIBUTE__(x)   __attribute__((x))
+#else
+#define THREAD_ANNOTATION_ATTRIBUTE__(x)   // no-op
+#endif
+
+// GUARDED_BY()
+//
+// Documents if a shared field or global variable needs to be protected by a
+// mutex. GUARDED_BY() allows the user to specify a particular mutex that
+// should be held when accessing the annotated variable.
+//
+// Although this annotation (and PT_GUARDED_BY, below) cannot be applied to
+// local variables, a local variable and its associated mutex can often be
+// combined into a small class or struct, thereby allowing the annotation.
+//
+// Example:
+//
+//   class Foo {
+//     Mutex mu_;
+//     int p1_ GUARDED_BY(mu_);
+//     ...
+//   };
+#define GUARDED_BY(x) THREAD_ANNOTATION_ATTRIBUTE__(guarded_by(x))
+
+// PT_GUARDED_BY()
+//
+// Documents if the memory location pointed to by a pointer should be guarded
+// by a mutex when dereferencing the pointer.
+//
+// Example:
+//   class Foo {
+//     Mutex mu_;
+//     int *p1_ PT_GUARDED_BY(mu_);
+//     ...
+//   };
+//
+// Note that a pointer variable to a shared memory location could itself be a
+// shared variable.
+//
+// Example:
+//
+//   // `q_`, guarded by `mu1_`, points to a shared memory location that is
+//   // guarded by `mu2_`:
+//   int *q_ GUARDED_BY(mu1_) PT_GUARDED_BY(mu2_);
+#define PT_GUARDED_BY(x) THREAD_ANNOTATION_ATTRIBUTE__(pt_guarded_by(x))
+
+// ACQUIRED_AFTER() / ACQUIRED_BEFORE()
+//
+// Documents the acquisition order between locks that can be held
+// simultaneously by a thread. For any two locks that need to be annotated
+// to establish an acquisition order, only one of them needs the annotation.
+// (i.e. You don't have to annotate both locks with both ACQUIRED_AFTER
+// and ACQUIRED_BEFORE.)
+//
+// As with GUARDED_BY, this is only applicable to mutexes that are shared
+// fields or global variables.
+//
+// Example:
+//
+//   Mutex m1_;
+//   Mutex m2_ ACQUIRED_AFTER(m1_);
+#define ACQUIRED_AFTER(...) \
+  THREAD_ANNOTATION_ATTRIBUTE__(acquired_after(__VA_ARGS__))
+
+#define ACQUIRED_BEFORE(...) \
+  THREAD_ANNOTATION_ATTRIBUTE__(acquired_before(__VA_ARGS__))
+
+// EXCLUSIVE_LOCKS_REQUIRED() / SHARED_LOCKS_REQUIRED()
+//
+// Documents a function that expects a mutex to be held prior to entry.
+// The mutex is expected to be held both on entry to, and exit from, the
+// function.
+//
+// An exclusive lock allows read-write access to the guarded data member(s), and
+// only one thread can acquire a lock exclusively at any one time. A shared lock
+// allows read-only access, and any number of threads can acquire a shared lock
+// concurrently.
+//
+// Generally, non-const methods should be annotated with
+// EXCLUSIVE_LOCKS_REQUIRED, while const methods should be annotated with
+// SHARED_LOCKS_REQUIRED.
+//
+// Example:
+//
+//   Mutex mu1, mu2;
+//   int a GUARDED_BY(mu1);
+//   int b GUARDED_BY(mu2);
+//
+//   void foo() EXCLUSIVE_LOCKS_REQUIRED(mu1, mu2) { ... }
+//   void bar() const SHARED_LOCKS_REQUIRED(mu1, mu2) { ... }
+#define EXCLUSIVE_LOCKS_REQUIRED(...) \
+  THREAD_ANNOTATION_ATTRIBUTE__(exclusive_locks_required(__VA_ARGS__))
+
+#define SHARED_LOCKS_REQUIRED(...) \
+  THREAD_ANNOTATION_ATTRIBUTE__(shared_locks_required(__VA_ARGS__))
+
+// LOCKS_EXCLUDED()
+//
+// Documents the locks acquired in the body of the function. These locks
+// cannot be held when calling this function (as Abseil's `Mutex` locks are
+// non-reentrant).
+#define LOCKS_EXCLUDED(...) \
+  THREAD_ANNOTATION_ATTRIBUTE__(locks_excluded(__VA_ARGS__))
+
+// LOCK_RETURNED()
+//
+// Documents a function that returns a mutex without acquiring it.  For example,
+// a public getter method that returns a pointer to a private mutex should
+// be annotated with LOCK_RETURNED.
+#define LOCK_RETURNED(x) \
+  THREAD_ANNOTATION_ATTRIBUTE__(lock_returned(x))
+
+// LOCKABLE
+//
+// Documents if a class/type is a lockable type (such as the `Mutex` class).
+#define LOCKABLE \
+  THREAD_ANNOTATION_ATTRIBUTE__(lockable)
+
+// SCOPED_LOCKABLE
+//
+// Documents if a class does RAII locking (such as the `MutexLock` class).
+// The constructor should use `LOCK_FUNCTION()` to specify the mutex that is
+// acquired, and the destructor should use `UNLOCK_FUNCTION()` with no
+// arguments; the analysis will assume that the destructor unlocks whatever the
+// constructor locked.
+#define SCOPED_LOCKABLE \
+  THREAD_ANNOTATION_ATTRIBUTE__(scoped_lockable)
+
+// EXCLUSIVE_LOCK_FUNCTION()
+//
+// Documents functions that acquire a lock in the body of a function, and do
+// not release it.
+#define EXCLUSIVE_LOCK_FUNCTION(...) \
+  THREAD_ANNOTATION_ATTRIBUTE__(exclusive_lock_function(__VA_ARGS__))
+
+// SHARED_LOCK_FUNCTION()
+//
+// Documents functions that acquire a shared (reader) lock in the body of a
+// function, and do not release it.
+#define SHARED_LOCK_FUNCTION(...) \
+  THREAD_ANNOTATION_ATTRIBUTE__(shared_lock_function(__VA_ARGS__))
+
+// UNLOCK_FUNCTION()
+//
+// Documents functions that expect a lock to be held on entry to the function,
+// and release it in the body of the function.
+#define UNLOCK_FUNCTION(...) \
+  THREAD_ANNOTATION_ATTRIBUTE__(unlock_function(__VA_ARGS__))
+
+// EXCLUSIVE_TRYLOCK_FUNCTION() / SHARED_TRYLOCK_FUNCTION()
+//
+// Documents functions that try to acquire a lock, and return success or failure
+// (or a non-boolean value that can be interpreted as a boolean).
+// The first argument should be `true` for functions that return `true` on
+// success, or `false` for functions that return `false` on success. The second
+// argument specifies the mutex that is locked on success. If unspecified, this
+// mutex is assumed to be `this`.
+#define EXCLUSIVE_TRYLOCK_FUNCTION(...) \
+  THREAD_ANNOTATION_ATTRIBUTE__(exclusive_trylock_function(__VA_ARGS__))
+
+#define SHARED_TRYLOCK_FUNCTION(...) \
+  THREAD_ANNOTATION_ATTRIBUTE__(shared_trylock_function(__VA_ARGS__))
+
+// ASSERT_EXCLUSIVE_LOCK() / ASSERT_SHARED_LOCK()
+//
+// Documents functions that dynamically check to see if a lock is held, and fail
+// if it is not held.
+#define ASSERT_EXCLUSIVE_LOCK(...) \
+  THREAD_ANNOTATION_ATTRIBUTE__(assert_exclusive_lock(__VA_ARGS__))
+
+#define ASSERT_SHARED_LOCK(...) \
+  THREAD_ANNOTATION_ATTRIBUTE__(assert_shared_lock(__VA_ARGS__))
+
+// NO_THREAD_SAFETY_ANALYSIS
+//
+// Turns off thread safety checking within the body of a particular function.
+// This annotation is used to mark functions that are known to be correct, but
+// the locking behavior is more complicated than the analyzer can handle.
+#define NO_THREAD_SAFETY_ANALYSIS \
+  THREAD_ANNOTATION_ATTRIBUTE__(no_thread_safety_analysis)
+
+//------------------------------------------------------------------------------
+// Tool-Supplied Annotations
+//------------------------------------------------------------------------------
+
+// TS_UNCHECKED should be placed around lock expressions that are not valid
+// C++ syntax, but which are present for documentation purposes.  These
+// annotations will be ignored by the analysis.
+#define TS_UNCHECKED(x) ""
+
+// TS_FIXME is used to mark lock expressions that are not valid C++ syntax.
+// It is used by automated tools to mark and disable invalid expressions.
+// The annotation should either be fixed, or changed to TS_UNCHECKED.
+#define TS_FIXME(x) ""
+
+// Like NO_THREAD_SAFETY_ANALYSIS, this turns off checking within the body of
+// a particular function.  However, this attribute is used to mark functions
+// that are incorrect and need to be fixed.  It is used by automated tools to
+// avoid breaking the build when the analysis is updated.
+// Code owners are expected to eventually fix the routine.
+#define NO_THREAD_SAFETY_ANALYSIS_FIXME  NO_THREAD_SAFETY_ANALYSIS
+
+// Similar to NO_THREAD_SAFETY_ANALYSIS_FIXME, this macro marks a GUARDED_BY
+// annotation that needs to be fixed, because it is producing thread safety
+// warning.  It disables the GUARDED_BY.
+#define GUARDED_BY_FIXME(x)
+
+// Disables warnings for a single read operation.  This can be used to avoid
+// warnings when it is known that the read is not actually involved in a race,
+// but the compiler cannot confirm that.
+#define TS_UNCHECKED_READ(x) thread_safety_analysis::ts_unchecked_read(x)
+
+
+namespace thread_safety_analysis {
+
+// Takes a reference to a guarded data member, and returns an unguarded
+// reference.
+template <typename T>
+inline const T& ts_unchecked_read(const T& v) NO_THREAD_SAFETY_ANALYSIS {
+  return v;
+}
+
+template <typename T>
+inline T& ts_unchecked_read(T& v) NO_THREAD_SAFETY_ANALYSIS {
+  return v;
+}
+
+}  // namespace thread_safety_analysis
+
+#endif  // ABSL_BASE_INTERNAL_THREAD_ANNOTATIONS_H_
--- a/include/absl/base/internal/thread_identity.h
+++ b/include/absl/base/internal/thread_identity.h
@ -0,0 +1,265 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// Each active thread has an ThreadIdentity that may represent the thread in
+// various level interfaces.  ThreadIdentity objects are never deallocated.
+// When a thread terminates, its ThreadIdentity object may be reused for a
+// thread created later.
+
+#ifndef ABSL_BASE_INTERNAL_THREAD_IDENTITY_H_
+#define ABSL_BASE_INTERNAL_THREAD_IDENTITY_H_
+
+#ifndef _WIN32
+#include <pthread.h>
+// Defines __GOOGLE_GRTE_VERSION__ (via glibc-specific features.h) when
+// supported.
+#include <unistd.h>
+#endif
+
+#include <atomic>
+#include <cstdint>
+
+#include "absl/base/config.h"
+#include "absl/base/internal/per_thread_tls.h"
+#include "absl/base/optimization.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+
+struct SynchLocksHeld;
+struct SynchWaitParams;
+
+namespace base_internal {
+
+class SpinLock;
+struct ThreadIdentity;
+
+// Used by the implementation of absl::Mutex and absl::CondVar.
+struct PerThreadSynch {
+  // The internal representation of absl::Mutex and absl::CondVar rely
+  // on the alignment of PerThreadSynch. Both store the address of the
+  // PerThreadSynch in the high-order bits of their internal state,
+  // which means the low kLowZeroBits of the address of PerThreadSynch
+  // must be zero.
+  static constexpr int kLowZeroBits = 8;
+  static constexpr int kAlignment = 1 << kLowZeroBits;
+
+  // Returns the associated ThreadIdentity.
+  // This can be implemented as a cast because we guarantee
+  // PerThreadSynch is the first element of ThreadIdentity.
+  ThreadIdentity* thread_identity() {
+    return reinterpret_cast<ThreadIdentity*>(this);
+  }
+
+  PerThreadSynch *next;  // Circular waiter queue; initialized to 0.
+  PerThreadSynch *skip;  // If non-zero, all entries in Mutex queue
+                         // up to and including "skip" have same
+                         // condition as this, and will be woken later
+  bool may_skip;         // if false while on mutex queue, a mutex unlocker
+                         // is using this PerThreadSynch as a terminator.  Its
+                         // skip field must not be filled in because the loop
+                         // might then skip over the terminator.
+  bool wake;             // This thread is to be woken from a Mutex.
+  // If "x" is on a waiter list for a mutex, "x->cond_waiter" is true iff the
+  // waiter is waiting on the mutex as part of a CV Wait or Mutex Await.
+  //
+  // The value of "x->cond_waiter" is meaningless if "x" is not on a
+  // Mutex waiter list.
+  bool cond_waiter;
+  bool maybe_unlocking;  // Valid at head of Mutex waiter queue;
+                         // true if UnlockSlow could be searching
+                         // for a waiter to wake.  Used for an optimization
+                         // in Enqueue().  true is always a valid value.
+                         // Can be reset to false when the unlocker or any
+                         // writer releases the lock, or a reader fully
+                         // releases the lock.  It may not be set to false
+                         // by a reader that decrements the count to
+                         // non-zero. protected by mutex spinlock
+  bool suppress_fatal_errors;  // If true, try to proceed even in the face
+                               // of broken invariants.  This is used within
+                               // fatal signal handlers to improve the
+                               // chances of debug logging information being
+                               // output successfully.
+  int priority;                // Priority of thread (updated every so often).
+
+  // State values:
+  //   kAvailable: This PerThreadSynch is available.
+  //   kQueued: This PerThreadSynch is unavailable, it's currently queued on a
+  //            Mutex or CondVar waistlist.
+  //
+  // Transitions from kQueued to kAvailable require a release
+  // barrier. This is needed as a waiter may use "state" to
+  // independently observe that it's no longer queued.
+  //
+  // Transitions from kAvailable to kQueued require no barrier, they
+  // are externally ordered by the Mutex.
+  enum State {
+    kAvailable,
+    kQueued
+  };
+  std::atomic<State> state;
+
+  // The wait parameters of the current wait.  waitp is null if the
+  // thread is not waiting. Transitions from null to non-null must
+  // occur before the enqueue commit point (state = kQueued in
+  // Enqueue() and CondVarEnqueue()). Transitions from non-null to
+  // null must occur after the wait is finished (state = kAvailable in
+  // Mutex::Block() and CondVar::WaitCommon()). This field may be
+  // changed only by the thread that describes this PerThreadSynch.  A
+  // special case is Fer(), which calls Enqueue() on another thread,
+  // but with an identical SynchWaitParams pointer, thus leaving the
+  // pointer unchanged.
+  SynchWaitParams* waitp;
+
+  intptr_t readers;     // Number of readers in mutex.
+
+  // When priority will next be read (cycles).
+  int64_t next_priority_read_cycles;
+
+  // Locks held; used during deadlock detection.
+  // Allocated in Synch_GetAllLocks() and freed in ReclaimThreadIdentity().
+  SynchLocksHeld *all_locks;
+};
+
+// The instances of this class are allocated in NewThreadIdentity() with an
+// alignment of PerThreadSynch::kAlignment.
+struct ThreadIdentity {
+  // Must be the first member.  The Mutex implementation requires that
+  // the PerThreadSynch object associated with each thread is
+  // PerThreadSynch::kAlignment aligned.  We provide this alignment on
+  // ThreadIdentity itself.
+  PerThreadSynch per_thread_synch;
+
+  // Private: Reserved for absl::synchronization_internal::Waiter.
+  struct WaiterState {
+    alignas(void*) char data[128];
+  } waiter_state;
+
+  // Used by PerThreadSem::{Get,Set}ThreadBlockedCounter().
+  std::atomic<int>* blocked_count_ptr;
+
+  // The following variables are mostly read/written just by the
+  // thread itself.  The only exception is that these are read by
+  // a ticker thread as a hint.
+  std::atomic<int> ticker;      // Tick counter, incremented once per second.
+  std::atomic<int> wait_start;  // Ticker value when thread started waiting.
+  std::atomic<bool> is_idle;    // Has thread become idle yet?
+
+  ThreadIdentity* next;
+};
+
+// Returns the ThreadIdentity object representing the calling thread; guaranteed
+// to be unique for its lifetime.  The returned object will remain valid for the
+// program's lifetime; although it may be re-assigned to a subsequent thread.
+// If one does not exist, return nullptr instead.
+//
+// Does not malloc(*), and is async-signal safe.
+// [*] Technically pthread_setspecific() does malloc on first use; however this
+// is handled internally within tcmalloc's initialization already.
+//
+// New ThreadIdentity objects can be constructed and associated with a thread
+// by calling GetOrCreateCurrentThreadIdentity() in per-thread-sem.h.
+ThreadIdentity* CurrentThreadIdentityIfPresent();
+
+using ThreadIdentityReclaimerFunction = void (*)(void*);
+
+// Sets the current thread identity to the given value.  'reclaimer' is a
+// pointer to the global function for cleaning up instances on thread
+// destruction.
+void SetCurrentThreadIdentity(ThreadIdentity* identity,
+                              ThreadIdentityReclaimerFunction reclaimer);
+
+// Removes the currently associated ThreadIdentity from the running thread.
+// This must be called from inside the ThreadIdentityReclaimerFunction, and only
+// from that function.
+void ClearCurrentThreadIdentity();
+
+// May be chosen at compile time via: -DABSL_FORCE_THREAD_IDENTITY_MODE=<mode
+// index>
+#ifdef ABSL_THREAD_IDENTITY_MODE_USE_POSIX_SETSPECIFIC
+#error ABSL_THREAD_IDENTITY_MODE_USE_POSIX_SETSPECIFIC cannot be directly set
+#else
+#define ABSL_THREAD_IDENTITY_MODE_USE_POSIX_SETSPECIFIC 0
+#endif
+
+#ifdef ABSL_THREAD_IDENTITY_MODE_USE_TLS
+#error ABSL_THREAD_IDENTITY_MODE_USE_TLS cannot be directly set
+#else
+#define ABSL_THREAD_IDENTITY_MODE_USE_TLS 1
+#endif
+
+#ifdef ABSL_THREAD_IDENTITY_MODE_USE_CPP11
+#error ABSL_THREAD_IDENTITY_MODE_USE_CPP11 cannot be directly set
+#else
+#define ABSL_THREAD_IDENTITY_MODE_USE_CPP11 2
+#endif
+
+#ifdef ABSL_THREAD_IDENTITY_MODE
+#error ABSL_THREAD_IDENTITY_MODE cannot be directly set
+#elif defined(ABSL_FORCE_THREAD_IDENTITY_MODE)
+#define ABSL_THREAD_IDENTITY_MODE ABSL_FORCE_THREAD_IDENTITY_MODE
+#elif defined(_WIN32) && !defined(__MINGW32__)
+#define ABSL_THREAD_IDENTITY_MODE ABSL_THREAD_IDENTITY_MODE_USE_CPP11
+#elif defined(__APPLE__) && defined(ABSL_HAVE_THREAD_LOCAL)
+#define ABSL_THREAD_IDENTITY_MODE ABSL_THREAD_IDENTITY_MODE_USE_CPP11
+#elif ABSL_PER_THREAD_TLS && defined(__GOOGLE_GRTE_VERSION__) &&        \
+    (__GOOGLE_GRTE_VERSION__ >= 20140228L)
+// Support for async-safe TLS was specifically added in GRTEv4.  It's not
+// present in the upstream eglibc.
+// Note:  Current default for production systems.
+#define ABSL_THREAD_IDENTITY_MODE ABSL_THREAD_IDENTITY_MODE_USE_TLS
+#else
+#define ABSL_THREAD_IDENTITY_MODE \
+  ABSL_THREAD_IDENTITY_MODE_USE_POSIX_SETSPECIFIC
+#endif
+
+#if ABSL_THREAD_IDENTITY_MODE == ABSL_THREAD_IDENTITY_MODE_USE_TLS || \
+    ABSL_THREAD_IDENTITY_MODE == ABSL_THREAD_IDENTITY_MODE_USE_CPP11
+
+#if ABSL_PER_THREAD_TLS
+ABSL_CONST_INIT extern ABSL_PER_THREAD_TLS_KEYWORD ThreadIdentity*
+    thread_identity_ptr;
+#elif defined(ABSL_HAVE_THREAD_LOCAL)
+ABSL_CONST_INIT extern thread_local ThreadIdentity* thread_identity_ptr;
+#else
+#error Thread-local storage not detected on this platform
+#endif
+
+// thread_local variables cannot be in headers exposed by DLLs or in certain
+// build configurations on Apple platforms. However, it is important for
+// performance reasons in general that `CurrentThreadIdentityIfPresent` be
+// inlined. In the other cases we opt to have the function not be inlined. Note
+// that `CurrentThreadIdentityIfPresent` is declared above so we can exclude
+// this entire inline definition.
+#if !defined(__APPLE__) && !defined(ABSL_BUILD_DLL) && \
+    !defined(ABSL_CONSUME_DLL)
+#define ABSL_INTERNAL_INLINE_CURRENT_THREAD_IDENTITY_IF_PRESENT 1
+#endif
+
+#ifdef ABSL_INTERNAL_INLINE_CURRENT_THREAD_IDENTITY_IF_PRESENT
+inline ThreadIdentity* CurrentThreadIdentityIfPresent() {
+  return thread_identity_ptr;
+}
+#endif
+
+#elif ABSL_THREAD_IDENTITY_MODE != \
+    ABSL_THREAD_IDENTITY_MODE_USE_POSIX_SETSPECIFIC
+#error Unknown ABSL_THREAD_IDENTITY_MODE
+#endif
+
+}  // namespace base_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_BASE_INTERNAL_THREAD_IDENTITY_H_
--- a/include/absl/base/internal/throw_delegate.h
+++ b/include/absl/base/internal/throw_delegate.h
@ -0,0 +1,75 @@
+//
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+#ifndef ABSL_BASE_INTERNAL_THROW_DELEGATE_H_
+#define ABSL_BASE_INTERNAL_THROW_DELEGATE_H_
+
+#include <string>
+
+#include "absl/base/config.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace base_internal {
+
+// Helper functions that allow throwing exceptions consistently from anywhere.
+// The main use case is for header-based libraries (eg templates), as they will
+// be built by many different targets with their own compiler options.
+// In particular, this will allow a safe way to throw exceptions even if the
+// caller is compiled with -fno-exceptions.  This is intended for implementing
+// things like map<>::at(), which the standard documents as throwing an
+// exception on error.
+//
+// Using other techniques like #if tricks could lead to ODR violations.
+//
+// You shouldn't use it unless you're writing code that you know will be built
+// both with and without exceptions and you need to conform to an interface
+// that uses exceptions.
+
+[[noreturn]] void ThrowStdLogicError(const std::string& what_arg);
+[[noreturn]] void ThrowStdLogicError(const char* what_arg);
+[[noreturn]] void ThrowStdInvalidArgument(const std::string& what_arg);
+[[noreturn]] void ThrowStdInvalidArgument(const char* what_arg);
+[[noreturn]] void ThrowStdDomainError(const std::string& what_arg);
+[[noreturn]] void ThrowStdDomainError(const char* what_arg);
+[[noreturn]] void ThrowStdLengthError(const std::string& what_arg);
+[[noreturn]] void ThrowStdLengthError(const char* what_arg);
+[[noreturn]] void ThrowStdOutOfRange(const std::string& what_arg);
+[[noreturn]] void ThrowStdOutOfRange(const char* what_arg);
+[[noreturn]] void ThrowStdRuntimeError(const std::string& what_arg);
+[[noreturn]] void ThrowStdRuntimeError(const char* what_arg);
+[[noreturn]] void ThrowStdRangeError(const std::string& what_arg);
+[[noreturn]] void ThrowStdRangeError(const char* what_arg);
+[[noreturn]] void ThrowStdOverflowError(const std::string& what_arg);
+[[noreturn]] void ThrowStdOverflowError(const char* what_arg);
+[[noreturn]] void ThrowStdUnderflowError(const std::string& what_arg);
+[[noreturn]] void ThrowStdUnderflowError(const char* what_arg);
+
+[[noreturn]] void ThrowStdBadFunctionCall();
+[[noreturn]] void ThrowStdBadAlloc();
+
+// ThrowStdBadArrayNewLength() cannot be consistently supported because
+// std::bad_array_new_length is missing in libstdc++ until 4.9.0.
+// https://gcc.gnu.org/onlinedocs/gcc-4.8.3/libstdc++/api/a01379_source.html
+// https://gcc.gnu.org/onlinedocs/gcc-4.9.0/libstdc++/api/a01327_source.html
+// libcxx (as of 3.2) and msvc (as of 2015) both have it.
+// [[noreturn]] void ThrowStdBadArrayNewLength();
+
+}  // namespace base_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_BASE_INTERNAL_THROW_DELEGATE_H_
--- a/include/absl/base/internal/tsan_mutex_interface.h
+++ b/include/absl/base/internal/tsan_mutex_interface.h
@ -0,0 +1,68 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// This file is intended solely for spinlock.h.
+// It provides ThreadSanitizer annotations for custom mutexes.
+// See <sanitizer/tsan_interface.h> for meaning of these annotations.
+
+#ifndef ABSL_BASE_INTERNAL_TSAN_MUTEX_INTERFACE_H_
+#define ABSL_BASE_INTERNAL_TSAN_MUTEX_INTERFACE_H_
+
+#include "absl/base/config.h"
+
+// ABSL_INTERNAL_HAVE_TSAN_INTERFACE
+// Macro intended only for internal use.
+//
+// Checks whether LLVM Thread Sanitizer interfaces are available.
+// First made available in LLVM 5.0 (Sep 2017).
+#ifdef ABSL_INTERNAL_HAVE_TSAN_INTERFACE
+#error "ABSL_INTERNAL_HAVE_TSAN_INTERFACE cannot be directly set."
+#endif
+
+#if defined(ABSL_HAVE_THREAD_SANITIZER) && defined(__has_include)
+#if __has_include(<sanitizer/tsan_interface.h>)
+#define ABSL_INTERNAL_HAVE_TSAN_INTERFACE 1
+#endif
+#endif
+
+#ifdef ABSL_INTERNAL_HAVE_TSAN_INTERFACE
+#include <sanitizer/tsan_interface.h>
+
+#define ABSL_TSAN_MUTEX_CREATE __tsan_mutex_create
+#define ABSL_TSAN_MUTEX_DESTROY __tsan_mutex_destroy
+#define ABSL_TSAN_MUTEX_PRE_LOCK __tsan_mutex_pre_lock
+#define ABSL_TSAN_MUTEX_POST_LOCK __tsan_mutex_post_lock
+#define ABSL_TSAN_MUTEX_PRE_UNLOCK __tsan_mutex_pre_unlock
+#define ABSL_TSAN_MUTEX_POST_UNLOCK __tsan_mutex_post_unlock
+#define ABSL_TSAN_MUTEX_PRE_SIGNAL __tsan_mutex_pre_signal
+#define ABSL_TSAN_MUTEX_POST_SIGNAL __tsan_mutex_post_signal
+#define ABSL_TSAN_MUTEX_PRE_DIVERT __tsan_mutex_pre_divert
+#define ABSL_TSAN_MUTEX_POST_DIVERT __tsan_mutex_post_divert
+
+#else
+
+#define ABSL_TSAN_MUTEX_CREATE(...)
+#define ABSL_TSAN_MUTEX_DESTROY(...)
+#define ABSL_TSAN_MUTEX_PRE_LOCK(...)
+#define ABSL_TSAN_MUTEX_POST_LOCK(...)
+#define ABSL_TSAN_MUTEX_PRE_UNLOCK(...)
+#define ABSL_TSAN_MUTEX_POST_UNLOCK(...)
+#define ABSL_TSAN_MUTEX_PRE_SIGNAL(...)
+#define ABSL_TSAN_MUTEX_POST_SIGNAL(...)
+#define ABSL_TSAN_MUTEX_PRE_DIVERT(...)
+#define ABSL_TSAN_MUTEX_POST_DIVERT(...)
+
+#endif
+
+#endif  // ABSL_BASE_INTERNAL_TSAN_MUTEX_INTERFACE_H_
--- a/include/absl/base/internal/unaligned_access.h
+++ b/include/absl/base/internal/unaligned_access.h
@ -0,0 +1,82 @@
+//
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+#ifndef ABSL_BASE_INTERNAL_UNALIGNED_ACCESS_H_
+#define ABSL_BASE_INTERNAL_UNALIGNED_ACCESS_H_
+
+#include <string.h>
+
+#include <cstdint>
+
+#include "absl/base/attributes.h"
+#include "absl/base/config.h"
+
+// unaligned APIs
+
+// Portable handling of unaligned loads, stores, and copies.
+
+// The unaligned API is C++ only.  The declarations use C++ features
+// (namespaces, inline) which are absent or incompatible in C.
+#if defined(__cplusplus)
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace base_internal {
+
+inline uint16_t UnalignedLoad16(const void *p) {
+  uint16_t t;
+  memcpy(&t, p, sizeof t);
+  return t;
+}
+
+inline uint32_t UnalignedLoad32(const void *p) {
+  uint32_t t;
+  memcpy(&t, p, sizeof t);
+  return t;
+}
+
+inline uint64_t UnalignedLoad64(const void *p) {
+  uint64_t t;
+  memcpy(&t, p, sizeof t);
+  return t;
+}
+
+inline void UnalignedStore16(void *p, uint16_t v) { memcpy(p, &v, sizeof v); }
+
+inline void UnalignedStore32(void *p, uint32_t v) { memcpy(p, &v, sizeof v); }
+
+inline void UnalignedStore64(void *p, uint64_t v) { memcpy(p, &v, sizeof v); }
+
+}  // namespace base_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#define ABSL_INTERNAL_UNALIGNED_LOAD16(_p) \
+  (absl::base_internal::UnalignedLoad16(_p))
+#define ABSL_INTERNAL_UNALIGNED_LOAD32(_p) \
+  (absl::base_internal::UnalignedLoad32(_p))
+#define ABSL_INTERNAL_UNALIGNED_LOAD64(_p) \
+  (absl::base_internal::UnalignedLoad64(_p))
+
+#define ABSL_INTERNAL_UNALIGNED_STORE16(_p, _val) \
+  (absl::base_internal::UnalignedStore16(_p, _val))
+#define ABSL_INTERNAL_UNALIGNED_STORE32(_p, _val) \
+  (absl::base_internal::UnalignedStore32(_p, _val))
+#define ABSL_INTERNAL_UNALIGNED_STORE64(_p, _val) \
+  (absl::base_internal::UnalignedStore64(_p, _val))
+
+#endif  // defined(__cplusplus), end of unaligned API
+
+#endif  // ABSL_BASE_INTERNAL_UNALIGNED_ACCESS_H_
--- a/include/absl/base/internal/unscaledcycleclock.h
+++ b/include/absl/base/internal/unscaledcycleclock.h
@ -0,0 +1,133 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// UnscaledCycleClock
+//    An UnscaledCycleClock yields the value and frequency of a cycle counter
+//    that increments at a rate that is approximately constant.
+//    This class is for internal use only, you should consider using CycleClock
+//    instead.
+//
+// Notes:
+// The cycle counter frequency is not necessarily the core clock frequency.
+// That is, CycleCounter cycles are not necessarily "CPU cycles".
+//
+// An arbitrary offset may have been added to the counter at power on.
+//
+// On some platforms, the rate and offset of the counter may differ
+// slightly when read from different CPUs of a multiprocessor.  Usually,
+// we try to ensure that the operating system adjusts values periodically
+// so that values agree approximately.   If you need stronger guarantees,
+// consider using alternate interfaces.
+//
+// The CPU is not required to maintain the ordering of a cycle counter read
+// with respect to surrounding instructions.
+
+#ifndef ABSL_BASE_INTERNAL_UNSCALEDCYCLECLOCK_H_
+#define ABSL_BASE_INTERNAL_UNSCALEDCYCLECLOCK_H_
+
+#include <cstdint>
+
+#if defined(__APPLE__)
+#include <TargetConditionals.h>
+#endif
+
+#include "absl/base/port.h"
+
+// The following platforms have an implementation of a hardware counter.
+#if defined(__i386__) || defined(__x86_64__) || defined(__aarch64__) || \
+    defined(__powerpc__) || defined(__ppc__) || defined(__riscv) ||     \
+    defined(_M_IX86) || (defined(_M_X64) && !defined(_M_ARM64EC))
+#define ABSL_HAVE_UNSCALED_CYCLECLOCK_IMPLEMENTATION 1
+#else
+#define ABSL_HAVE_UNSCALED_CYCLECLOCK_IMPLEMENTATION 0
+#endif
+
+// The following platforms often disable access to the hardware
+// counter (through a sandbox) even if the underlying hardware has a
+// usable counter. The CycleTimer interface also requires a *scaled*
+// CycleClock that runs at atleast 1 MHz. We've found some Android
+// ARM64 devices where this is not the case, so we disable it by
+// default on Android ARM64.
+#if defined(__native_client__) || (defined(__APPLE__)) || \
+    (defined(__ANDROID__) && defined(__aarch64__))
+#define ABSL_USE_UNSCALED_CYCLECLOCK_DEFAULT 0
+#else
+#define ABSL_USE_UNSCALED_CYCLECLOCK_DEFAULT 1
+#endif
+
+// UnscaledCycleClock is an optional internal feature.
+// Use "#if ABSL_USE_UNSCALED_CYCLECLOCK" to test for its presence.
+// Can be overridden at compile-time via -DABSL_USE_UNSCALED_CYCLECLOCK=0|1
+#if !defined(ABSL_USE_UNSCALED_CYCLECLOCK)
+#define ABSL_USE_UNSCALED_CYCLECLOCK               \
+  (ABSL_HAVE_UNSCALED_CYCLECLOCK_IMPLEMENTATION && \
+   ABSL_USE_UNSCALED_CYCLECLOCK_DEFAULT)
+#endif
+
+#if ABSL_USE_UNSCALED_CYCLECLOCK
+
+// This macro can be used to test if UnscaledCycleClock::Frequency()
+// is NominalCPUFrequency() on a particular platform.
+#if (defined(__i386__) || defined(__x86_64__) || defined(__riscv) || \
+     defined(_M_IX86) || defined(_M_X64))
+#define ABSL_INTERNAL_UNSCALED_CYCLECLOCK_FREQUENCY_IS_CPU_FREQUENCY
+#endif
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace time_internal {
+class UnscaledCycleClockWrapperForGetCurrentTime;
+}  // namespace time_internal
+
+namespace base_internal {
+class CycleClock;
+class UnscaledCycleClockWrapperForInitializeFrequency;
+
+class UnscaledCycleClock {
+ private:
+  UnscaledCycleClock() = delete;
+
+  // Return the value of a cycle counter that counts at a rate that is
+  // approximately constant.
+  static int64_t Now();
+
+  // Return the how much UnscaledCycleClock::Now() increases per second.
+  // This is not necessarily the core CPU clock frequency.
+  // It may be the nominal value report by the kernel, rather than a measured
+  // value.
+  static double Frequency();
+
+  // Allowed users
+  friend class base_internal::CycleClock;
+  friend class time_internal::UnscaledCycleClockWrapperForGetCurrentTime;
+  friend class base_internal::UnscaledCycleClockWrapperForInitializeFrequency;
+};
+
+#if defined(__x86_64__)
+
+inline int64_t UnscaledCycleClock::Now() {
+  uint64_t low, high;
+  __asm__ volatile("rdtsc" : "=a"(low), "=d"(high));
+  return (high << 32) | low;
+}
+
+#endif
+
+}  // namespace base_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_USE_UNSCALED_CYCLECLOCK
+
+#endif  // ABSL_BASE_INTERNAL_UNSCALEDCYCLECLOCK_H_
--- a/include/absl/base/log_severity.h
+++ b/include/absl/base/log_severity.h
@ -0,0 +1,172 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef ABSL_BASE_LOG_SEVERITY_H_
+#define ABSL_BASE_LOG_SEVERITY_H_
+
+#include <array>
+#include <ostream>
+
+#include "absl/base/attributes.h"
+#include "absl/base/config.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+
+// absl::LogSeverity
+//
+// Four severity levels are defined. Logging APIs should terminate the program
+// when a message is logged at severity `kFatal`; the other levels have no
+// special semantics.
+//
+// Values other than the four defined levels (e.g. produced by `static_cast`)
+// are valid, but their semantics when passed to a function, macro, or flag
+// depend on the function, macro, or flag. The usual behavior is to normalize
+// such values to a defined severity level, however in some cases values other
+// than the defined levels are useful for comparison.
+//
+// Example:
+//
+//   // Effectively disables all logging:
+//   SetMinLogLevel(static_cast<absl::LogSeverity>(100));
+//
+// Abseil flags may be defined with type `LogSeverity`. Dependency layering
+// constraints require that the `AbslParseFlag()` overload be declared and
+// defined in the flags library itself rather than here. The `AbslUnparseFlag()`
+// overload is defined there as well for consistency.
+//
+// absl::LogSeverity Flag String Representation
+//
+// An `absl::LogSeverity` has a string representation used for parsing
+// command-line flags based on the enumerator name (e.g. `kFatal`) or
+// its unprefixed name (without the `k`) in any case-insensitive form. (E.g.
+// "FATAL", "fatal" or "Fatal" are all valid.) Unparsing such flags produces an
+// unprefixed string representation in all caps (e.g. "FATAL") or an integer.
+//
+// Additionally, the parser accepts arbitrary integers (as if the type were
+// `int`).
+//
+// Examples:
+//
+//   --my_log_level=kInfo
+//   --my_log_level=INFO
+//   --my_log_level=info
+//   --my_log_level=0
+//
+// Unparsing a flag produces the same result as `absl::LogSeverityName()` for
+// the standard levels and a base-ten integer otherwise.
+enum class LogSeverity : int {
+  kInfo = 0,
+  kWarning = 1,
+  kError = 2,
+  kFatal = 3,
+};
+
+// LogSeverities()
+//
+// Returns an iterable of all standard `absl::LogSeverity` values, ordered from
+// least to most severe.
+constexpr std::array<absl::LogSeverity, 4> LogSeverities() {
+  return {{absl::LogSeverity::kInfo, absl::LogSeverity::kWarning,
+           absl::LogSeverity::kError, absl::LogSeverity::kFatal}};
+}
+
+// LogSeverityName()
+//
+// Returns the all-caps string representation (e.g. "INFO") of the specified
+// severity level if it is one of the standard levels and "UNKNOWN" otherwise.
+constexpr const char* LogSeverityName(absl::LogSeverity s) {
+  return s == absl::LogSeverity::kInfo
+             ? "INFO"
+             : s == absl::LogSeverity::kWarning
+                   ? "WARNING"
+                   : s == absl::LogSeverity::kError
+                         ? "ERROR"
+                         : s == absl::LogSeverity::kFatal ? "FATAL" : "UNKNOWN";
+}
+
+// NormalizeLogSeverity()
+//
+// Values less than `kInfo` normalize to `kInfo`; values greater than `kFatal`
+// normalize to `kError` (**NOT** `kFatal`).
+constexpr absl::LogSeverity NormalizeLogSeverity(absl::LogSeverity s) {
+  return s < absl::LogSeverity::kInfo
+             ? absl::LogSeverity::kInfo
+             : s > absl::LogSeverity::kFatal ? absl::LogSeverity::kError : s;
+}
+constexpr absl::LogSeverity NormalizeLogSeverity(int s) {
+  return absl::NormalizeLogSeverity(static_cast<absl::LogSeverity>(s));
+}
+
+// operator<<
+//
+// The exact representation of a streamed `absl::LogSeverity` is deliberately
+// unspecified; do not rely on it.
+std::ostream& operator<<(std::ostream& os, absl::LogSeverity s);
+
+// Enums representing a lower bound for LogSeverity. APIs that only operate on
+// messages of at least a certain level (for example, `SetMinLogLevel()`) use
+// this type to specify that level. absl::LogSeverityAtLeast::kInfinity is
+// a level above all threshold levels and therefore no log message will
+// ever meet this threshold.
+enum class LogSeverityAtLeast : int {
+  kInfo = static_cast<int>(absl::LogSeverity::kInfo),
+  kWarning = static_cast<int>(absl::LogSeverity::kWarning),
+  kError = static_cast<int>(absl::LogSeverity::kError),
+  kFatal = static_cast<int>(absl::LogSeverity::kFatal),
+  kInfinity = 1000,
+};
+
+std::ostream& operator<<(std::ostream& os, absl::LogSeverityAtLeast s);
+
+// Enums representing an upper bound for LogSeverity. APIs that only operate on
+// messages of at most a certain level (for example, buffer all messages at or
+// below a certain level) use this type to specify that level.
+// absl::LogSeverityAtMost::kNegativeInfinity is a level below all threshold
+// levels and therefore will exclude all log messages.
+enum class LogSeverityAtMost : int {
+  kNegativeInfinity = -1000,
+  kInfo = static_cast<int>(absl::LogSeverity::kInfo),
+  kWarning = static_cast<int>(absl::LogSeverity::kWarning),
+  kError = static_cast<int>(absl::LogSeverity::kError),
+  kFatal = static_cast<int>(absl::LogSeverity::kFatal),
+};
+
+std::ostream& operator<<(std::ostream& os, absl::LogSeverityAtMost s);
+
+#define COMPOP(op1, op2, T)                                         \
+  constexpr bool operator op1(absl::T lhs, absl::LogSeverity rhs) { \
+    return static_cast<absl::LogSeverity>(lhs) op1 rhs;             \
+  }                                                                 \
+  constexpr bool operator op2(absl::LogSeverity lhs, absl::T rhs) { \
+    return lhs op2 static_cast<absl::LogSeverity>(rhs);             \
+  }
+
+// Comparisons between `LogSeverity` and `LogSeverityAtLeast`/
+// `LogSeverityAtMost` are only supported in one direction.
+// Valid checks are:
+//   LogSeverity >= LogSeverityAtLeast
+//   LogSeverity < LogSeverityAtLeast
+//   LogSeverity <= LogSeverityAtMost
+//   LogSeverity > LogSeverityAtMost
+COMPOP(>, <, LogSeverityAtLeast)
+COMPOP(<=, >=, LogSeverityAtLeast)
+COMPOP(<, >, LogSeverityAtMost)
+COMPOP(>=, <=, LogSeverityAtMost)
+#undef COMPOP
+
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_BASE_LOG_SEVERITY_H_
--- a/include/absl/base/macros.h
+++ b/include/absl/base/macros.h
@ -0,0 +1,158 @@
+//
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// -----------------------------------------------------------------------------
+// File: macros.h
+// -----------------------------------------------------------------------------
+//
+// This header file defines the set of language macros used within Abseil code.
+// For the set of macros used to determine supported compilers and platforms,
+// see absl/base/config.h instead.
+//
+// This code is compiled directly on many platforms, including client
+// platforms like Windows, Mac, and embedded systems.  Before making
+// any changes here, make sure that you're not breaking any platforms.
+
+#ifndef ABSL_BASE_MACROS_H_
+#define ABSL_BASE_MACROS_H_
+
+#include <cassert>
+#include <cstddef>
+
+#include "absl/base/attributes.h"
+#include "absl/base/config.h"
+#include "absl/base/optimization.h"
+#include "absl/base/port.h"
+
+// ABSL_ARRAYSIZE()
+//
+// Returns the number of elements in an array as a compile-time constant, which
+// can be used in defining new arrays. If you use this macro on a pointer by
+// mistake, you will get a compile-time error.
+#define ABSL_ARRAYSIZE(array) \
+  (sizeof(::absl::macros_internal::ArraySizeHelper(array)))
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace macros_internal {
+// Note: this internal template function declaration is used by ABSL_ARRAYSIZE.
+// The function doesn't need a definition, as we only use its type.
+template <typename T, size_t N>
+auto ArraySizeHelper(const T (&array)[N]) -> char (&)[N];
+}  // namespace macros_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+// ABSL_BAD_CALL_IF()
+//
+// Used on a function overload to trap bad calls: any call that matches the
+// overload will cause a compile-time error. This macro uses a clang-specific
+// "enable_if" attribute, as described at
+// https://clang.llvm.org/docs/AttributeReference.html#enable-if
+//
+// Overloads which use this macro should be bracketed by
+// `#ifdef ABSL_BAD_CALL_IF`.
+//
+// Example:
+//
+//   int isdigit(int c);
+//   #ifdef ABSL_BAD_CALL_IF
+//   int isdigit(int c)
+//     ABSL_BAD_CALL_IF(c <= -1 || c > 255,
+//                       "'c' must have the value of an unsigned char or EOF");
+//   #endif // ABSL_BAD_CALL_IF
+#if ABSL_HAVE_ATTRIBUTE(enable_if)
+#define ABSL_BAD_CALL_IF(expr, msg) \
+  __attribute__((enable_if(expr, "Bad call trap"), unavailable(msg)))
+#endif
+
+// ABSL_ASSERT()
+//
+// In C++11, `assert` can't be used portably within constexpr functions.
+// ABSL_ASSERT functions as a runtime assert but works in C++11 constexpr
+// functions.  Example:
+//
+// constexpr double Divide(double a, double b) {
+//   return ABSL_ASSERT(b != 0), a / b;
+// }
+//
+// This macro is inspired by
+// https://akrzemi1.wordpress.com/2017/05/18/asserts-in-constexpr-functions/
+#if defined(NDEBUG)
+#define ABSL_ASSERT(expr) \
+  (false ? static_cast<void>(expr) : static_cast<void>(0))
+#else
+#define ABSL_ASSERT(expr)                           \
+  (ABSL_PREDICT_TRUE((expr)) ? static_cast<void>(0) \
+                             : [] { assert(false && #expr); }())  // NOLINT
+#endif
+
+// `ABSL_INTERNAL_HARDENING_ABORT()` controls how `ABSL_HARDENING_ASSERT()`
+// aborts the program in release mode (when NDEBUG is defined). The
+// implementation should abort the program as quickly as possible and ideally it
+// should not be possible to ignore the abort request.
+#if (ABSL_HAVE_BUILTIN(__builtin_trap) &&         \
+     ABSL_HAVE_BUILTIN(__builtin_unreachable)) || \
+    (defined(__GNUC__) && !defined(__clang__))
+#define ABSL_INTERNAL_HARDENING_ABORT() \
+  do {                                  \
+    __builtin_trap();                   \
+    __builtin_unreachable();            \
+  } while (false)
+#else
+#define ABSL_INTERNAL_HARDENING_ABORT() abort()
+#endif
+
+// ABSL_HARDENING_ASSERT()
+//
+// `ABSL_HARDENING_ASSERT()` is like `ABSL_ASSERT()`, but used to implement
+// runtime assertions that should be enabled in hardened builds even when
+// `NDEBUG` is defined.
+//
+// When `NDEBUG` is not defined, `ABSL_HARDENING_ASSERT()` is identical to
+// `ABSL_ASSERT()`.
+//
+// See `ABSL_OPTION_HARDENED` in `absl/base/options.h` for more information on
+// hardened mode.
+#if ABSL_OPTION_HARDENED == 1 && defined(NDEBUG)
+#define ABSL_HARDENING_ASSERT(expr)                 \
+  (ABSL_PREDICT_TRUE((expr)) ? static_cast<void>(0) \
+                             : [] { ABSL_INTERNAL_HARDENING_ABORT(); }())
+#else
+#define ABSL_HARDENING_ASSERT(expr) ABSL_ASSERT(expr)
+#endif
+
+#ifdef ABSL_HAVE_EXCEPTIONS
+#define ABSL_INTERNAL_TRY try
+#define ABSL_INTERNAL_CATCH_ANY catch (...)
+#define ABSL_INTERNAL_RETHROW do { throw; } while (false)
+#else  // ABSL_HAVE_EXCEPTIONS
+#define ABSL_INTERNAL_TRY if (true)
+#define ABSL_INTERNAL_CATCH_ANY else if (false)
+#define ABSL_INTERNAL_RETHROW do {} while (false)
+#endif  // ABSL_HAVE_EXCEPTIONS
+
+// `ABSL_INTERNAL_UNREACHABLE` is an unreachable statement.  A program which
+// reaches one has undefined behavior, and the compiler may optimize
+// accordingly.
+#if defined(__GNUC__) || ABSL_HAVE_BUILTIN(__builtin_unreachable)
+#define ABSL_INTERNAL_UNREACHABLE __builtin_unreachable()
+#elif defined(_MSC_VER)
+#define ABSL_INTERNAL_UNREACHABLE __assume(0)
+#else
+#define ABSL_INTERNAL_UNREACHABLE
+#endif
+
+#endif  // ABSL_BASE_MACROS_H_
--- a/include/absl/base/optimization.h
+++ b/include/absl/base/optimization.h
@ -0,0 +1,252 @@
+//
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// -----------------------------------------------------------------------------
+// File: optimization.h
+// -----------------------------------------------------------------------------
+//
+// This header file defines portable macros for performance optimization.
+
+#ifndef ABSL_BASE_OPTIMIZATION_H_
+#define ABSL_BASE_OPTIMIZATION_H_
+
+#include <assert.h>
+
+#include "absl/base/config.h"
+
+// ABSL_BLOCK_TAIL_CALL_OPTIMIZATION
+//
+// Instructs the compiler to avoid optimizing tail-call recursion. This macro is
+// useful when you wish to preserve the existing function order within a stack
+// trace for logging, debugging, or profiling purposes.
+//
+// Example:
+//
+//   int f() {
+//     int result = g();
+//     ABSL_BLOCK_TAIL_CALL_OPTIMIZATION();
+//     return result;
+//   }
+#if defined(__pnacl__)
+#define ABSL_BLOCK_TAIL_CALL_OPTIMIZATION() if (volatile int x = 0) { (void)x; }
+#elif defined(__clang__)
+// Clang will not tail call given inline volatile assembly.
+#define ABSL_BLOCK_TAIL_CALL_OPTIMIZATION() __asm__ __volatile__("")
+#elif defined(__GNUC__)
+// GCC will not tail call given inline volatile assembly.
+#define ABSL_BLOCK_TAIL_CALL_OPTIMIZATION() __asm__ __volatile__("")
+#elif defined(_MSC_VER)
+#include <intrin.h>
+// The __nop() intrinsic blocks the optimisation.
+#define ABSL_BLOCK_TAIL_CALL_OPTIMIZATION() __nop()
+#else
+#define ABSL_BLOCK_TAIL_CALL_OPTIMIZATION() if (volatile int x = 0) { (void)x; }
+#endif
+
+// ABSL_CACHELINE_SIZE
+//
+// Explicitly defines the size of the L1 cache for purposes of alignment.
+// Setting the cacheline size allows you to specify that certain objects be
+// aligned on a cacheline boundary with `ABSL_CACHELINE_ALIGNED` declarations.
+// (See below.)
+//
+// NOTE: this macro should be replaced with the following C++17 features, when
+// those are generally available:
+//
+//   * `std::hardware_constructive_interference_size`
+//   * `std::hardware_destructive_interference_size`
+//
+// See http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/p0154r1.html
+// for more information.
+#if defined(__GNUC__)
+// Cache line alignment
+#if defined(__i386__) || defined(__x86_64__)
+#define ABSL_CACHELINE_SIZE 64
+#elif defined(__powerpc64__)
+#define ABSL_CACHELINE_SIZE 128
+#elif defined(__aarch64__)
+// We would need to read special register ctr_el0 to find out L1 dcache size.
+// This value is a good estimate based on a real aarch64 machine.
+#define ABSL_CACHELINE_SIZE 64
+#elif defined(__arm__)
+// Cache line sizes for ARM: These values are not strictly correct since
+// cache line sizes depend on implementations, not architectures.  There
+// are even implementations with cache line sizes configurable at boot
+// time.
+#if defined(__ARM_ARCH_5T__)
+#define ABSL_CACHELINE_SIZE 32
+#elif defined(__ARM_ARCH_7A__)
+#define ABSL_CACHELINE_SIZE 64
+#endif
+#endif
+
+#ifndef ABSL_CACHELINE_SIZE
+// A reasonable default guess.  Note that overestimates tend to waste more
+// space, while underestimates tend to waste more time.
+#define ABSL_CACHELINE_SIZE 64
+#endif
+
+// ABSL_CACHELINE_ALIGNED
+//
+// Indicates that the declared object be cache aligned using
+// `ABSL_CACHELINE_SIZE` (see above). Cacheline aligning objects allows you to
+// load a set of related objects in the L1 cache for performance improvements.
+// Cacheline aligning objects properly allows constructive memory sharing and
+// prevents destructive (or "false") memory sharing.
+//
+// NOTE: callers should replace uses of this macro with `alignas()` using
+// `std::hardware_constructive_interference_size` and/or
+// `std::hardware_destructive_interference_size` when C++17 becomes available to
+// them.
+//
+// See http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/p0154r1.html
+// for more information.
+//
+// On some compilers, `ABSL_CACHELINE_ALIGNED` expands to an `__attribute__`
+// or `__declspec` attribute. For compilers where this is not known to work,
+// the macro expands to nothing.
+//
+// No further guarantees are made here. The result of applying the macro
+// to variables and types is always implementation-defined.
+//
+// WARNING: It is easy to use this attribute incorrectly, even to the point
+// of causing bugs that are difficult to diagnose, crash, etc. It does not
+// of itself guarantee that objects are aligned to a cache line.
+//
+// NOTE: Some compilers are picky about the locations of annotations such as
+// this attribute, so prefer to put it at the beginning of your declaration.
+// For example,
+//
+//   ABSL_CACHELINE_ALIGNED static Foo* foo = ...
+//
+//   class ABSL_CACHELINE_ALIGNED Bar { ...
+//
+// Recommendations:
+//
+// 1) Consult compiler documentation; this comment is not kept in sync as
+//    toolchains evolve.
+// 2) Verify your use has the intended effect. This often requires inspecting
+//    the generated machine code.
+// 3) Prefer applying this attribute to individual variables. Avoid
+//    applying it to types. This tends to localize the effect.
+#define ABSL_CACHELINE_ALIGNED __attribute__((aligned(ABSL_CACHELINE_SIZE)))
+#elif defined(_MSC_VER)
+#define ABSL_CACHELINE_SIZE 64
+#define ABSL_CACHELINE_ALIGNED __declspec(align(ABSL_CACHELINE_SIZE))
+#else
+#define ABSL_CACHELINE_SIZE 64
+#define ABSL_CACHELINE_ALIGNED
+#endif
+
+// ABSL_PREDICT_TRUE, ABSL_PREDICT_FALSE
+//
+// Enables the compiler to prioritize compilation using static analysis for
+// likely paths within a boolean branch.
+//
+// Example:
+//
+//   if (ABSL_PREDICT_TRUE(expression)) {
+//     return result;                        // Faster if more likely
+//   } else {
+//     return 0;
+//   }
+//
+// Compilers can use the information that a certain branch is not likely to be
+// taken (for instance, a CHECK failure) to optimize for the common case in
+// the absence of better information (ie. compiling gcc with `-fprofile-arcs`).
+//
+// Recommendation: Modern CPUs dynamically predict branch execution paths,
+// typically with accuracy greater than 97%. As a result, annotating every
+// branch in a codebase is likely counterproductive; however, annotating
+// specific branches that are both hot and consistently mispredicted is likely
+// to yield performance improvements.
+#if ABSL_HAVE_BUILTIN(__builtin_expect) || \
+    (defined(__GNUC__) && !defined(__clang__))
+#define ABSL_PREDICT_FALSE(x) (__builtin_expect(false || (x), false))
+#define ABSL_PREDICT_TRUE(x) (__builtin_expect(false || (x), true))
+#else
+#define ABSL_PREDICT_FALSE(x) (x)
+#define ABSL_PREDICT_TRUE(x) (x)
+#endif
+
+// ABSL_ASSUME(cond)
+//
+// Informs the compiler that a condition is always true and that it can assume
+// it to be true for optimization purposes.
+//
+// WARNING: If the condition is false, the program can produce undefined and
+// potentially dangerous behavior.
+//
+// In !NDEBUG mode, the condition is checked with an assert().
+//
+// NOTE: The expression must not have side effects, as it may only be evaluated
+// in some compilation modes and not others. Some compilers may issue a warning
+// if the compiler cannot prove the expression has no side effects. For example,
+// the expression should not use a function call since the compiler cannot prove
+// that a function call does not have side effects.
+//
+// Example:
+//
+//   int x = ...;
+//   ABSL_ASSUME(x >= 0);
+//   // The compiler can optimize the division to a simple right shift using the
+//   // assumption specified above.
+//   int y = x / 16;
+//
+#if !defined(NDEBUG)
+#define ABSL_ASSUME(cond) assert(cond)
+#elif ABSL_HAVE_BUILTIN(__builtin_assume)
+#define ABSL_ASSUME(cond) __builtin_assume(cond)
+#elif defined(__GNUC__) || ABSL_HAVE_BUILTIN(__builtin_unreachable)
+#define ABSL_ASSUME(cond)                 \
+  do {                                    \
+    if (!(cond)) __builtin_unreachable(); \
+  } while (0)
+#elif defined(_MSC_VER)
+#define ABSL_ASSUME(cond) __assume(cond)
+#else
+#define ABSL_ASSUME(cond)               \
+  do {                                  \
+    static_cast<void>(false && (cond)); \
+  } while (0)
+#endif
+
+// ABSL_INTERNAL_UNIQUE_SMALL_NAME(cond)
+// This macro forces small unique name on a static file level symbols like
+// static local variables or static functions. This is intended to be used in
+// macro definitions to optimize the cost of generated code. Do NOT use it on
+// symbols exported from translation unit since it may cause a link time
+// conflict.
+//
+// Example:
+//
+// #define MY_MACRO(txt)
+// namespace {
+//  char VeryVeryLongVarName[] ABSL_INTERNAL_UNIQUE_SMALL_NAME() = txt;
+//  const char* VeryVeryLongFuncName() ABSL_INTERNAL_UNIQUE_SMALL_NAME();
+//  const char* VeryVeryLongFuncName() { return txt; }
+// }
+//
+
+#if defined(__GNUC__)
+#define ABSL_INTERNAL_UNIQUE_SMALL_NAME2(x) #x
+#define ABSL_INTERNAL_UNIQUE_SMALL_NAME1(x) ABSL_INTERNAL_UNIQUE_SMALL_NAME2(x)
+#define ABSL_INTERNAL_UNIQUE_SMALL_NAME() \
+  asm(ABSL_INTERNAL_UNIQUE_SMALL_NAME1(.absl.__COUNTER__))
+#else
+#define ABSL_INTERNAL_UNIQUE_SMALL_NAME()
+#endif
+
+#endif  // ABSL_BASE_OPTIMIZATION_H_
--- a/include/absl/base/options.h
+++ b/include/absl/base/options.h
@ -0,0 +1,238 @@
+// Copyright 2019 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// -----------------------------------------------------------------------------
+// File: options.h
+// -----------------------------------------------------------------------------
+//
+// This file contains Abseil configuration options for setting specific
+// implementations instead of letting Abseil determine which implementation to
+// use at compile-time. Setting these options may be useful for package or build
+// managers who wish to guarantee ABI stability within binary builds (which are
+// otherwise difficult to enforce).
+//
+// *** IMPORTANT NOTICE FOR PACKAGE MANAGERS:  It is important that
+// maintainers of package managers who wish to package Abseil read and
+// understand this file! ***
+//
+// Abseil contains a number of possible configuration endpoints, based on
+// parameters such as the detected platform, language version, or command-line
+// flags used to invoke the underlying binary. As is the case with all
+// libraries, binaries which contain Abseil code must ensure that separate
+// packages use the same compiled copy of Abseil to avoid a diamond dependency
+// problem, which can occur if two packages built with different Abseil
+// configuration settings are linked together. Diamond dependency problems in
+// C++ may manifest as violations to the One Definition Rule (ODR) (resulting in
+// linker errors), or undefined behavior (resulting in crashes).
+//
+// Diamond dependency problems can be avoided if all packages utilize the same
+// exact version of Abseil. Building from source code with the same compilation
+// parameters is the easiest way to avoid such dependency problems. However, for
+// package managers who cannot control such compilation parameters, we are
+// providing the file to allow you to inject ABI (Application Binary Interface)
+// stability across builds. Settings options in this file will neither change
+// API nor ABI, providing a stable copy of Abseil between packages.
+//
+// Care must be taken to keep options within these configurations isolated
+// from any other dynamic settings, such as command-line flags which could alter
+// these options. This file is provided specifically to help build and package
+// managers provide a stable copy of Abseil within their libraries and binaries;
+// other developers should not have need to alter the contents of this file.
+//
+// -----------------------------------------------------------------------------
+// Usage
+// -----------------------------------------------------------------------------
+//
+// For any particular package release, set the appropriate definitions within
+// this file to whatever value makes the most sense for your package(s). Note
+// that, by default, most of these options, at the moment, affect the
+// implementation of types; future options may affect other implementation
+// details.
+//
+// NOTE: the defaults within this file all assume that Abseil can select the
+// proper Abseil implementation at compile-time, which will not be sufficient
+// to guarantee ABI stability to package managers.
+
+#ifndef ABSL_BASE_OPTIONS_H_
+#define ABSL_BASE_OPTIONS_H_
+
+// Include a standard library header to allow configuration based on the
+// standard library in use.
+#ifdef __cplusplus
+#include <ciso646>
+#endif
+
+// -----------------------------------------------------------------------------
+// Type Compatibility Options
+// -----------------------------------------------------------------------------
+//
+// ABSL_OPTION_USE_STD_ANY
+//
+// This option controls whether absl::any is implemented as an alias to
+// std::any, or as an independent implementation.
+//
+// A value of 0 means to use Abseil's implementation.  This requires only C++11
+// support, and is expected to work on every toolchain we support.
+//
+// A value of 1 means to use an alias to std::any.  This requires that all code
+// using Abseil is built in C++17 mode or later.
+//
+// A value of 2 means to detect the C++ version being used to compile Abseil,
+// and use an alias only if a working std::any is available.  This option is
+// useful when you are building your entire program, including all of its
+// dependencies, from source.  It should not be used otherwise -- for example,
+// if you are distributing Abseil in a binary package manager -- since in
+// mode 2, absl::any will name a different type, with a different mangled name
+// and binary layout, depending on the compiler flags passed by the end user.
+// For more info, see https://abseil.io/about/design/dropin-types.
+//
+// User code should not inspect this macro.  To check in the preprocessor if
+// absl::any is a typedef of std::any, use the feature macro ABSL_USES_STD_ANY.
+
+#define ABSL_OPTION_USE_STD_ANY 2
+
+
+// ABSL_OPTION_USE_STD_OPTIONAL
+//
+// This option controls whether absl::optional is implemented as an alias to
+// std::optional, or as an independent implementation.
+//
+// A value of 0 means to use Abseil's implementation.  This requires only C++11
+// support, and is expected to work on every toolchain we support.
+//
+// A value of 1 means to use an alias to std::optional.  This requires that all
+// code using Abseil is built in C++17 mode or later.
+//
+// A value of 2 means to detect the C++ version being used to compile Abseil,
+// and use an alias only if a working std::optional is available.  This option
+// is useful when you are building your program from source.  It should not be
+// used otherwise -- for example, if you are distributing Abseil in a binary
+// package manager -- since in mode 2, absl::optional will name a different
+// type, with a different mangled name and binary layout, depending on the
+// compiler flags passed by the end user.  For more info, see
+// https://abseil.io/about/design/dropin-types.
+
+// User code should not inspect this macro.  To check in the preprocessor if
+// absl::optional is a typedef of std::optional, use the feature macro
+// ABSL_USES_STD_OPTIONAL.
+
+#define ABSL_OPTION_USE_STD_OPTIONAL 2
+
+
+// ABSL_OPTION_USE_STD_STRING_VIEW
+//
+// This option controls whether absl::string_view is implemented as an alias to
+// std::string_view, or as an independent implementation.
+//
+// A value of 0 means to use Abseil's implementation.  This requires only C++11
+// support, and is expected to work on every toolchain we support.
+//
+// A value of 1 means to use an alias to std::string_view.  This requires that
+// all code using Abseil is built in C++17 mode or later.
+//
+// A value of 2 means to detect the C++ version being used to compile Abseil,
+// and use an alias only if a working std::string_view is available.  This
+// option is useful when you are building your program from source.  It should
+// not be used otherwise -- for example, if you are distributing Abseil in a
+// binary package manager -- since in mode 2, absl::string_view will name a
+// different type, with a different mangled name and binary layout, depending on
+// the compiler flags passed by the end user.  For more info, see
+// https://abseil.io/about/design/dropin-types.
+//
+// User code should not inspect this macro.  To check in the preprocessor if
+// absl::string_view is a typedef of std::string_view, use the feature macro
+// ABSL_USES_STD_STRING_VIEW.
+
+#define ABSL_OPTION_USE_STD_STRING_VIEW 2
+
+// ABSL_OPTION_USE_STD_VARIANT
+//
+// This option controls whether absl::variant is implemented as an alias to
+// std::variant, or as an independent implementation.
+//
+// A value of 0 means to use Abseil's implementation.  This requires only C++11
+// support, and is expected to work on every toolchain we support.
+//
+// A value of 1 means to use an alias to std::variant.  This requires that all
+// code using Abseil is built in C++17 mode or later.
+//
+// A value of 2 means to detect the C++ version being used to compile Abseil,
+// and use an alias only if a working std::variant is available.  This option
+// is useful when you are building your program from source.  It should not be
+// used otherwise -- for example, if you are distributing Abseil in a binary
+// package manager -- since in mode 2, absl::variant will name a different
+// type, with a different mangled name and binary layout, depending on the
+// compiler flags passed by the end user.  For more info, see
+// https://abseil.io/about/design/dropin-types.
+//
+// User code should not inspect this macro.  To check in the preprocessor if
+// absl::variant is a typedef of std::variant, use the feature macro
+// ABSL_USES_STD_VARIANT.
+
+#define ABSL_OPTION_USE_STD_VARIANT 2
+
+
+// ABSL_OPTION_USE_INLINE_NAMESPACE
+// ABSL_OPTION_INLINE_NAMESPACE_NAME
+//
+// These options controls whether all entities in the absl namespace are
+// contained within an inner inline namespace.  This does not affect the
+// user-visible API of Abseil, but it changes the mangled names of all symbols.
+//
+// This can be useful as a version tag if you are distributing Abseil in
+// precompiled form.  This will prevent a binary library build of Abseil with
+// one inline namespace being used with headers configured with a different
+// inline namespace name.  Binary packagers are reminded that Abseil does not
+// guarantee any ABI stability in Abseil, so any update of Abseil or
+// configuration change in such a binary package should be combined with a
+// new, unique value for the inline namespace name.
+//
+// A value of 0 means not to use inline namespaces.
+//
+// A value of 1 means to use an inline namespace with the given name inside
+// namespace absl.  If this is set, ABSL_OPTION_INLINE_NAMESPACE_NAME must also
+// be changed to a new, unique identifier name.  In particular "head" is not
+// allowed.
+
+#define ABSL_OPTION_USE_INLINE_NAMESPACE 1
+#define ABSL_OPTION_INLINE_NAMESPACE_NAME lts_20220623
+
+// ABSL_OPTION_HARDENED
+//
+// This option enables a "hardened" build in release mode (in this context,
+// release mode is defined as a build where the `NDEBUG` macro is defined).
+//
+// A value of 0 means that "hardened" mode is not enabled.
+//
+// A value of 1 means that "hardened" mode is enabled.
+//
+// Hardened builds have additional security checks enabled when `NDEBUG` is
+// defined. Defining `NDEBUG` is normally used to turn `assert()` macro into a
+// no-op, as well as disabling other bespoke program consistency checks. By
+// defining ABSL_OPTION_HARDENED to 1, a select set of checks remain enabled in
+// release mode. These checks guard against programming errors that may lead to
+// security vulnerabilities. In release mode, when one of these programming
+// errors is encountered, the program will immediately abort, possibly without
+// any attempt at logging.
+//
+// The checks enabled by this option are not free; they do incur runtime cost.
+//
+// The checks enabled by this option are always active when `NDEBUG` is not
+// defined, even in the case when ABSL_OPTION_HARDENED is defined to 0. The
+// checks enabled by this option may abort the program in a different way and
+// log additional information when `NDEBUG` is not defined.
+
+#define ABSL_OPTION_HARDENED 0
+
+#endif  // ABSL_BASE_OPTIONS_H_
--- a/include/absl/base/policy_checks.h
+++ b/include/absl/base/policy_checks.h
@ -0,0 +1,111 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// -----------------------------------------------------------------------------
+// File: policy_checks.h
+// -----------------------------------------------------------------------------
+//
+// This header enforces a minimum set of policies at build time, such as the
+// supported compiler and library versions. Unsupported configurations are
+// reported with `#error`. This enforcement is best effort, so successfully
+// compiling this header does not guarantee a supported configuration.
+
+#ifndef ABSL_BASE_POLICY_CHECKS_H_
+#define ABSL_BASE_POLICY_CHECKS_H_
+
+// Included for the __GLIBC_PREREQ macro used below.
+#include <limits.h>
+
+// Included for the _STLPORT_VERSION macro used below.
+#if defined(__cplusplus)
+#include <cstddef>
+#endif
+
+// -----------------------------------------------------------------------------
+// Operating System Check
+// -----------------------------------------------------------------------------
+
+#if defined(__CYGWIN__)
+#error "Cygwin is not supported."
+#endif
+
+// -----------------------------------------------------------------------------
+// Toolchain Check
+// -----------------------------------------------------------------------------
+
+// We support MSVC++ 14.0 update 2 and later.
+// This minimum will go up.
+#if defined(_MSC_FULL_VER) && _MSC_FULL_VER < 190023918 && !defined(__clang__)
+#error "This package requires Visual Studio 2015 Update 2 or higher."
+#endif
+
+// We support gcc 4.7 and later.
+// This minimum will go up.
+#if defined(__GNUC__) && !defined(__clang__)
+#if __GNUC__ < 4 || (__GNUC__ == 4 && __GNUC_MINOR__ < 7)
+#error "This package requires gcc 4.7 or higher."
+#endif
+#endif
+
+// We support Apple Xcode clang 4.2.1 (version 421.11.65) and later.
+// This corresponds to Apple Xcode version 4.5.
+// This minimum will go up.
+#if defined(__apple_build_version__) && __apple_build_version__ < 4211165
+#error "This package requires __apple_build_version__ of 4211165 or higher."
+#endif
+
+// -----------------------------------------------------------------------------
+// C++ Version Check
+// -----------------------------------------------------------------------------
+
+// Enforce C++11 as the minimum.  Note that Visual Studio has not
+// advanced __cplusplus despite being good enough for our purposes, so
+// so we exempt it from the check.
+#if defined(__cplusplus) && !defined(_MSC_VER)
+#if __cplusplus < 201103L
+#error "C++ versions less than C++11 are not supported."
+#endif
+#endif
+
+// -----------------------------------------------------------------------------
+// Standard Library Check
+// -----------------------------------------------------------------------------
+
+#if defined(_STLPORT_VERSION)
+#error "STLPort is not supported."
+#endif
+
+// -----------------------------------------------------------------------------
+// `char` Size Check
+// -----------------------------------------------------------------------------
+
+// Abseil currently assumes CHAR_BIT == 8. If you would like to use Abseil on a
+// platform where this is not the case, please provide us with the details about
+// your platform so we can consider relaxing this requirement.
+#if CHAR_BIT != 8
+#error "Abseil assumes CHAR_BIT == 8."
+#endif
+
+// -----------------------------------------------------------------------------
+// `int` Size Check
+// -----------------------------------------------------------------------------
+
+// Abseil currently assumes that an int is 4 bytes. If you would like to use
+// Abseil on a platform where this is not the case, please provide us with the
+// details about your platform so we can consider relaxing this requirement.
+#if INT_MAX < 2147483647
+#error "Abseil assumes that int is at least 4 bytes. "
+#endif
+
+#endif  // ABSL_BASE_POLICY_CHECKS_H_
--- a/include/absl/base/port.h
+++ b/include/absl/base/port.h
@ -0,0 +1,25 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// This files is a forwarding header for other headers containing various
+// portability macros and functions.
+
+#ifndef ABSL_BASE_PORT_H_
+#define ABSL_BASE_PORT_H_
+
+#include "absl/base/attributes.h"
+#include "absl/base/config.h"
+#include "absl/base/optimization.h"
+
+#endif  // ABSL_BASE_PORT_H_
--- a/include/absl/base/thread_annotations.h
+++ b/include/absl/base/thread_annotations.h
@ -0,0 +1,335 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// -----------------------------------------------------------------------------
+// File: thread_annotations.h
+// -----------------------------------------------------------------------------
+//
+// This header file contains macro definitions for thread safety annotations
+// that allow developers to document the locking policies of multi-threaded
+// code. The annotations can also help program analysis tools to identify
+// potential thread safety issues.
+//
+// These annotations are implemented using compiler attributes. Using the macros
+// defined here instead of raw attributes allow for portability and future
+// compatibility.
+//
+// When referring to mutexes in the arguments of the attributes, you should
+// use variable names or more complex expressions (e.g. my_object->mutex_)
+// that evaluate to a concrete mutex object whenever possible. If the mutex
+// you want to refer to is not in scope, you may use a member pointer
+// (e.g. &MyClass::mutex_) to refer to a mutex in some (unknown) object.
+
+#ifndef ABSL_BASE_THREAD_ANNOTATIONS_H_
+#define ABSL_BASE_THREAD_ANNOTATIONS_H_
+
+#include "absl/base/attributes.h"
+#include "absl/base/config.h"
+// TODO(mbonadei): Remove after the backward compatibility period.
+#include "absl/base/internal/thread_annotations.h"  // IWYU pragma: export
+
+// ABSL_GUARDED_BY()
+//
+// Documents if a shared field or global variable needs to be protected by a
+// mutex. ABSL_GUARDED_BY() allows the user to specify a particular mutex that
+// should be held when accessing the annotated variable.
+//
+// Although this annotation (and ABSL_PT_GUARDED_BY, below) cannot be applied to
+// local variables, a local variable and its associated mutex can often be
+// combined into a small class or struct, thereby allowing the annotation.
+//
+// Example:
+//
+//   class Foo {
+//     Mutex mu_;
+//     int p1_ ABSL_GUARDED_BY(mu_);
+//     ...
+//   };
+#if ABSL_HAVE_ATTRIBUTE(guarded_by)
+#define ABSL_GUARDED_BY(x) __attribute__((guarded_by(x)))
+#else
+#define ABSL_GUARDED_BY(x)
+#endif
+
+// ABSL_PT_GUARDED_BY()
+//
+// Documents if the memory location pointed to by a pointer should be guarded
+// by a mutex when dereferencing the pointer.
+//
+// Example:
+//   class Foo {
+//     Mutex mu_;
+//     int *p1_ ABSL_PT_GUARDED_BY(mu_);
+//     ...
+//   };
+//
+// Note that a pointer variable to a shared memory location could itself be a
+// shared variable.
+//
+// Example:
+//
+//   // `q_`, guarded by `mu1_`, points to a shared memory location that is
+//   // guarded by `mu2_`:
+//   int *q_ ABSL_GUARDED_BY(mu1_) ABSL_PT_GUARDED_BY(mu2_);
+#if ABSL_HAVE_ATTRIBUTE(pt_guarded_by)
+#define ABSL_PT_GUARDED_BY(x) __attribute__((pt_guarded_by(x)))
+#else
+#define ABSL_PT_GUARDED_BY(x)
+#endif
+
+// ABSL_ACQUIRED_AFTER() / ABSL_ACQUIRED_BEFORE()
+//
+// Documents the acquisition order between locks that can be held
+// simultaneously by a thread. For any two locks that need to be annotated
+// to establish an acquisition order, only one of them needs the annotation.
+// (i.e. You don't have to annotate both locks with both ABSL_ACQUIRED_AFTER
+// and ABSL_ACQUIRED_BEFORE.)
+//
+// As with ABSL_GUARDED_BY, this is only applicable to mutexes that are shared
+// fields or global variables.
+//
+// Example:
+//
+//   Mutex m1_;
+//   Mutex m2_ ABSL_ACQUIRED_AFTER(m1_);
+#if ABSL_HAVE_ATTRIBUTE(acquired_after)
+#define ABSL_ACQUIRED_AFTER(...) __attribute__((acquired_after(__VA_ARGS__)))
+#else
+#define ABSL_ACQUIRED_AFTER(...)
+#endif
+
+#if ABSL_HAVE_ATTRIBUTE(acquired_before)
+#define ABSL_ACQUIRED_BEFORE(...) __attribute__((acquired_before(__VA_ARGS__)))
+#else
+#define ABSL_ACQUIRED_BEFORE(...)
+#endif
+
+// ABSL_EXCLUSIVE_LOCKS_REQUIRED() / ABSL_SHARED_LOCKS_REQUIRED()
+//
+// Documents a function that expects a mutex to be held prior to entry.
+// The mutex is expected to be held both on entry to, and exit from, the
+// function.
+//
+// An exclusive lock allows read-write access to the guarded data member(s), and
+// only one thread can acquire a lock exclusively at any one time. A shared lock
+// allows read-only access, and any number of threads can acquire a shared lock
+// concurrently.
+//
+// Generally, non-const methods should be annotated with
+// ABSL_EXCLUSIVE_LOCKS_REQUIRED, while const methods should be annotated with
+// ABSL_SHARED_LOCKS_REQUIRED.
+//
+// Example:
+//
+//   Mutex mu1, mu2;
+//   int a ABSL_GUARDED_BY(mu1);
+//   int b ABSL_GUARDED_BY(mu2);
+//
+//   void foo() ABSL_EXCLUSIVE_LOCKS_REQUIRED(mu1, mu2) { ... }
+//   void bar() const ABSL_SHARED_LOCKS_REQUIRED(mu1, mu2) { ... }
+#if ABSL_HAVE_ATTRIBUTE(exclusive_locks_required)
+#define ABSL_EXCLUSIVE_LOCKS_REQUIRED(...) \
+  __attribute__((exclusive_locks_required(__VA_ARGS__)))
+#else
+#define ABSL_EXCLUSIVE_LOCKS_REQUIRED(...)
+#endif
+
+#if ABSL_HAVE_ATTRIBUTE(shared_locks_required)
+#define ABSL_SHARED_LOCKS_REQUIRED(...) \
+  __attribute__((shared_locks_required(__VA_ARGS__)))
+#else
+#define ABSL_SHARED_LOCKS_REQUIRED(...)
+#endif
+
+// ABSL_LOCKS_EXCLUDED()
+//
+// Documents the locks that cannot be held by callers of this function, as they
+// might be acquired by this function (Abseil's `Mutex` locks are
+// non-reentrant).
+#if ABSL_HAVE_ATTRIBUTE(locks_excluded)
+#define ABSL_LOCKS_EXCLUDED(...) __attribute__((locks_excluded(__VA_ARGS__)))
+#else
+#define ABSL_LOCKS_EXCLUDED(...)
+#endif
+
+// ABSL_LOCK_RETURNED()
+//
+// Documents a function that returns a mutex without acquiring it.  For example,
+// a public getter method that returns a pointer to a private mutex should
+// be annotated with ABSL_LOCK_RETURNED.
+#if ABSL_HAVE_ATTRIBUTE(lock_returned)
+#define ABSL_LOCK_RETURNED(x) __attribute__((lock_returned(x)))
+#else
+#define ABSL_LOCK_RETURNED(x)
+#endif
+
+// ABSL_LOCKABLE
+//
+// Documents if a class/type is a lockable type (such as the `Mutex` class).
+#if ABSL_HAVE_ATTRIBUTE(lockable)
+#define ABSL_LOCKABLE __attribute__((lockable))
+#else
+#define ABSL_LOCKABLE
+#endif
+
+// ABSL_SCOPED_LOCKABLE
+//
+// Documents if a class does RAII locking (such as the `MutexLock` class).
+// The constructor should use `LOCK_FUNCTION()` to specify the mutex that is
+// acquired, and the destructor should use `UNLOCK_FUNCTION()` with no
+// arguments; the analysis will assume that the destructor unlocks whatever the
+// constructor locked.
+#if ABSL_HAVE_ATTRIBUTE(scoped_lockable)
+#define ABSL_SCOPED_LOCKABLE __attribute__((scoped_lockable))
+#else
+#define ABSL_SCOPED_LOCKABLE
+#endif
+
+// ABSL_EXCLUSIVE_LOCK_FUNCTION()
+//
+// Documents functions that acquire a lock in the body of a function, and do
+// not release it.
+#if ABSL_HAVE_ATTRIBUTE(exclusive_lock_function)
+#define ABSL_EXCLUSIVE_LOCK_FUNCTION(...) \
+  __attribute__((exclusive_lock_function(__VA_ARGS__)))
+#else
+#define ABSL_EXCLUSIVE_LOCK_FUNCTION(...)
+#endif
+
+// ABSL_SHARED_LOCK_FUNCTION()
+//
+// Documents functions that acquire a shared (reader) lock in the body of a
+// function, and do not release it.
+#if ABSL_HAVE_ATTRIBUTE(shared_lock_function)
+#define ABSL_SHARED_LOCK_FUNCTION(...) \
+  __attribute__((shared_lock_function(__VA_ARGS__)))
+#else
+#define ABSL_SHARED_LOCK_FUNCTION(...)
+#endif
+
+// ABSL_UNLOCK_FUNCTION()
+//
+// Documents functions that expect a lock to be held on entry to the function,
+// and release it in the body of the function.
+#if ABSL_HAVE_ATTRIBUTE(unlock_function)
+#define ABSL_UNLOCK_FUNCTION(...) __attribute__((unlock_function(__VA_ARGS__)))
+#else
+#define ABSL_UNLOCK_FUNCTION(...)
+#endif
+
+// ABSL_EXCLUSIVE_TRYLOCK_FUNCTION() / ABSL_SHARED_TRYLOCK_FUNCTION()
+//
+// Documents functions that try to acquire a lock, and return success or failure
+// (or a non-boolean value that can be interpreted as a boolean).
+// The first argument should be `true` for functions that return `true` on
+// success, or `false` for functions that return `false` on success. The second
+// argument specifies the mutex that is locked on success. If unspecified, this
+// mutex is assumed to be `this`.
+#if ABSL_HAVE_ATTRIBUTE(exclusive_trylock_function)
+#define ABSL_EXCLUSIVE_TRYLOCK_FUNCTION(...) \
+  __attribute__((exclusive_trylock_function(__VA_ARGS__)))
+#else
+#define ABSL_EXCLUSIVE_TRYLOCK_FUNCTION(...)
+#endif
+
+#if ABSL_HAVE_ATTRIBUTE(shared_trylock_function)
+#define ABSL_SHARED_TRYLOCK_FUNCTION(...) \
+  __attribute__((shared_trylock_function(__VA_ARGS__)))
+#else
+#define ABSL_SHARED_TRYLOCK_FUNCTION(...)
+#endif
+
+// ABSL_ASSERT_EXCLUSIVE_LOCK() / ABSL_ASSERT_SHARED_LOCK()
+//
+// Documents functions that dynamically check to see if a lock is held, and fail
+// if it is not held.
+#if ABSL_HAVE_ATTRIBUTE(assert_exclusive_lock)
+#define ABSL_ASSERT_EXCLUSIVE_LOCK(...) \
+  __attribute__((assert_exclusive_lock(__VA_ARGS__)))
+#else
+#define ABSL_ASSERT_EXCLUSIVE_LOCK(...)
+#endif
+
+#if ABSL_HAVE_ATTRIBUTE(assert_shared_lock)
+#define ABSL_ASSERT_SHARED_LOCK(...) \
+  __attribute__((assert_shared_lock(__VA_ARGS__)))
+#else
+#define ABSL_ASSERT_SHARED_LOCK(...)
+#endif
+
+// ABSL_NO_THREAD_SAFETY_ANALYSIS
+//
+// Turns off thread safety checking within the body of a particular function.
+// This annotation is used to mark functions that are known to be correct, but
+// the locking behavior is more complicated than the analyzer can handle.
+#if ABSL_HAVE_ATTRIBUTE(no_thread_safety_analysis)
+#define ABSL_NO_THREAD_SAFETY_ANALYSIS \
+  __attribute__((no_thread_safety_analysis))
+#else
+#define ABSL_NO_THREAD_SAFETY_ANALYSIS
+#endif
+
+//------------------------------------------------------------------------------
+// Tool-Supplied Annotations
+//------------------------------------------------------------------------------
+
+// ABSL_TS_UNCHECKED should be placed around lock expressions that are not valid
+// C++ syntax, but which are present for documentation purposes.  These
+// annotations will be ignored by the analysis.
+#define ABSL_TS_UNCHECKED(x) ""
+
+// ABSL_TS_FIXME is used to mark lock expressions that are not valid C++ syntax.
+// It is used by automated tools to mark and disable invalid expressions.
+// The annotation should either be fixed, or changed to ABSL_TS_UNCHECKED.
+#define ABSL_TS_FIXME(x) ""
+
+// Like ABSL_NO_THREAD_SAFETY_ANALYSIS, this turns off checking within the body
+// of a particular function.  However, this attribute is used to mark functions
+// that are incorrect and need to be fixed.  It is used by automated tools to
+// avoid breaking the build when the analysis is updated.
+// Code owners are expected to eventually fix the routine.
+#define ABSL_NO_THREAD_SAFETY_ANALYSIS_FIXME ABSL_NO_THREAD_SAFETY_ANALYSIS
+
+// Similar to ABSL_NO_THREAD_SAFETY_ANALYSIS_FIXME, this macro marks a
+// ABSL_GUARDED_BY annotation that needs to be fixed, because it is producing
+// thread safety warning. It disables the ABSL_GUARDED_BY.
+#define ABSL_GUARDED_BY_FIXME(x)
+
+// Disables warnings for a single read operation.  This can be used to avoid
+// warnings when it is known that the read is not actually involved in a race,
+// but the compiler cannot confirm that.
+#define ABSL_TS_UNCHECKED_READ(x) absl::base_internal::ts_unchecked_read(x)
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace base_internal {
+
+// Takes a reference to a guarded data member, and returns an unguarded
+// reference.
+// Do not use this function directly, use ABSL_TS_UNCHECKED_READ instead.
+template <typename T>
+inline const T& ts_unchecked_read(const T& v) ABSL_NO_THREAD_SAFETY_ANALYSIS {
+  return v;
+}
+
+template <typename T>
+inline T& ts_unchecked_read(T& v) ABSL_NO_THREAD_SAFETY_ANALYSIS {
+  return v;
+}
+
+}  // namespace base_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_BASE_THREAD_ANNOTATIONS_H_
--- a/include/absl/cleanup/cleanup.h
+++ b/include/absl/cleanup/cleanup.h
@ -0,0 +1,140 @@
+// Copyright 2021 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// -----------------------------------------------------------------------------
+// File: cleanup.h
+// -----------------------------------------------------------------------------
+//
+// `absl::Cleanup` implements the scope guard idiom, invoking the contained
+// callback's `operator()() &&` on scope exit.
+//
+// Example:
+//
+// ```
+//   absl::Status CopyGoodData(const char* source_path, const char* sink_path) {
+//     FILE* source_file = fopen(source_path, "r");
+//     if (source_file == nullptr) {
+//       return absl::NotFoundError("No source file");  // No cleanups execute
+//     }
+//
+//     // C++17 style cleanup using class template argument deduction
+//     absl::Cleanup source_closer = [source_file] { fclose(source_file); };
+//
+//     FILE* sink_file = fopen(sink_path, "w");
+//     if (sink_file == nullptr) {
+//       return absl::NotFoundError("No sink file");  // First cleanup executes
+//     }
+//
+//     // C++11 style cleanup using the factory function
+//     auto sink_closer = absl::MakeCleanup([sink_file] { fclose(sink_file); });
+//
+//     Data data;
+//     while (ReadData(source_file, &data)) {
+//       if (!data.IsGood()) {
+//         absl::Status result = absl::FailedPreconditionError("Read bad data");
+//         return result;  // Both cleanups execute
+//       }
+//       SaveData(sink_file, &data);
+//     }
+//
+//     return absl::OkStatus();  // Both cleanups execute
+//   }
+// ```
+//
+// Methods:
+//
+// `std::move(cleanup).Cancel()` will prevent the callback from executing.
+//
+// `std::move(cleanup).Invoke()` will execute the callback early, before
+// destruction, and prevent the callback from executing in the destructor.
+//
+// Usage:
+//
+// `absl::Cleanup` is not an interface type. It is only intended to be used
+// within the body of a function. It is not a value type and instead models a
+// control flow construct. Check out `defer` in Golang for something similar.
+
+#ifndef ABSL_CLEANUP_CLEANUP_H_
+#define ABSL_CLEANUP_CLEANUP_H_
+
+#include <utility>
+
+#include "absl/base/config.h"
+#include "absl/base/macros.h"
+#include "absl/cleanup/internal/cleanup.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+
+template <typename Arg, typename Callback = void()>
+class ABSL_MUST_USE_RESULT Cleanup final {
+  static_assert(cleanup_internal::WasDeduced<Arg>(),
+                "Explicit template parameters are not supported.");
+
+  static_assert(cleanup_internal::ReturnsVoid<Callback>(),
+                "Callbacks that return values are not supported.");
+
+ public:
+  Cleanup(Callback callback) : storage_(std::move(callback)) {}  // NOLINT
+
+  Cleanup(Cleanup&& other) = default;
+
+  void Cancel() && {
+    ABSL_HARDENING_ASSERT(storage_.IsCallbackEngaged());
+    storage_.DestroyCallback();
+  }
+
+  void Invoke() && {
+    ABSL_HARDENING_ASSERT(storage_.IsCallbackEngaged());
+    storage_.InvokeCallback();
+    storage_.DestroyCallback();
+  }
+
+  ~Cleanup() {
+    if (storage_.IsCallbackEngaged()) {
+      storage_.InvokeCallback();
+      storage_.DestroyCallback();
+    }
+  }
+
+ private:
+  cleanup_internal::Storage<Callback> storage_;
+};
+
+// `absl::Cleanup c = /* callback */;`
+//
+// C++17 type deduction API for creating an instance of `absl::Cleanup`
+#if defined(ABSL_HAVE_CLASS_TEMPLATE_ARGUMENT_DEDUCTION)
+template <typename Callback>
+Cleanup(Callback callback) -> Cleanup<cleanup_internal::Tag, Callback>;
+#endif  // defined(ABSL_HAVE_CLASS_TEMPLATE_ARGUMENT_DEDUCTION)
+
+// `auto c = absl::MakeCleanup(/* callback */);`
+//
+// C++11 type deduction API for creating an instance of `absl::Cleanup`
+template <typename... Args, typename Callback>
+absl::Cleanup<cleanup_internal::Tag, Callback> MakeCleanup(Callback callback) {
+  static_assert(cleanup_internal::WasDeduced<cleanup_internal::Tag, Args...>(),
+                "Explicit template parameters are not supported.");
+
+  static_assert(cleanup_internal::ReturnsVoid<Callback>(),
+                "Callbacks that return values are not supported.");
+
+  return {std::move(callback)};
+}
+
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_CLEANUP_CLEANUP_H_
--- a/include/absl/cleanup/internal/cleanup.h
+++ b/include/absl/cleanup/internal/cleanup.h
@ -0,0 +1,100 @@
+// Copyright 2021 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef ABSL_CLEANUP_INTERNAL_CLEANUP_H_
+#define ABSL_CLEANUP_INTERNAL_CLEANUP_H_
+
+#include <new>
+#include <type_traits>
+#include <utility>
+
+#include "absl/base/internal/invoke.h"
+#include "absl/base/macros.h"
+#include "absl/base/thread_annotations.h"
+#include "absl/utility/utility.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+
+namespace cleanup_internal {
+
+struct Tag {};
+
+template <typename Arg, typename... Args>
+constexpr bool WasDeduced() {
+  return (std::is_same<cleanup_internal::Tag, Arg>::value) &&
+         (sizeof...(Args) == 0);
+}
+
+template <typename Callback>
+constexpr bool ReturnsVoid() {
+  return (std::is_same<base_internal::invoke_result_t<Callback>, void>::value);
+}
+
+template <typename Callback>
+class Storage {
+ public:
+  Storage() = delete;
+
+  explicit Storage(Callback callback) {
+    // Placement-new into a character buffer is used for eager destruction when
+    // the cleanup is invoked or cancelled. To ensure this optimizes well, the
+    // behavior is implemented locally instead of using an absl::optional.
+    ::new (GetCallbackBuffer()) Callback(std::move(callback));
+    is_callback_engaged_ = true;
+  }
+
+  Storage(Storage&& other) {
+    ABSL_HARDENING_ASSERT(other.IsCallbackEngaged());
+
+    ::new (GetCallbackBuffer()) Callback(std::move(other.GetCallback()));
+    is_callback_engaged_ = true;
+
+    other.DestroyCallback();
+  }
+
+  Storage(const Storage& other) = delete;
+
+  Storage& operator=(Storage&& other) = delete;
+
+  Storage& operator=(const Storage& other) = delete;
+
+  void* GetCallbackBuffer() { return static_cast<void*>(+callback_buffer_); }
+
+  Callback& GetCallback() {
+    return *reinterpret_cast<Callback*>(GetCallbackBuffer());
+  }
+
+  bool IsCallbackEngaged() const { return is_callback_engaged_; }
+
+  void DestroyCallback() {
+    is_callback_engaged_ = false;
+    GetCallback().~Callback();
+  }
+
+  void InvokeCallback() ABSL_NO_THREAD_SAFETY_ANALYSIS {
+    std::move(GetCallback())();
+  }
+
+ private:
+  bool is_callback_engaged_;
+  alignas(Callback) char callback_buffer_[sizeof(Callback)];
+};
+
+}  // namespace cleanup_internal
+
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_CLEANUP_INTERNAL_CLEANUP_H_
--- a/include/absl/container/btree_map.h
+++ b/include/absl/container/btree_map.h
@ -0,0 +1,851 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// -----------------------------------------------------------------------------
+// File: btree_map.h
+// -----------------------------------------------------------------------------
+//
+// This header file defines B-tree maps: sorted associative containers mapping
+// keys to values.
+//
+//     * `absl::btree_map<>`
+//     * `absl::btree_multimap<>`
+//
+// These B-tree types are similar to the corresponding types in the STL
+// (`std::map` and `std::multimap`) and generally conform to the STL interfaces
+// of those types. However, because they are implemented using B-trees, they
+// are more efficient in most situations.
+//
+// Unlike `std::map` and `std::multimap`, which are commonly implemented using
+// red-black tree nodes, B-tree maps use more generic B-tree nodes able to hold
+// multiple values per node. Holding multiple values per node often makes
+// B-tree maps perform better than their `std::map` counterparts, because
+// multiple entries can be checked within the same cache hit.
+//
+// However, these types should not be considered drop-in replacements for
+// `std::map` and `std::multimap` as there are some API differences, which are
+// noted in this header file. The most consequential differences with respect to
+// migrating to b-tree from the STL types are listed in the next paragraph.
+// Other API differences are minor.
+//
+// Importantly, insertions and deletions may invalidate outstanding iterators,
+// pointers, and references to elements. Such invalidations are typically only
+// an issue if insertion and deletion operations are interleaved with the use of
+// more than one iterator, pointer, or reference simultaneously. For this
+// reason, `insert()` and `erase()` return a valid iterator at the current
+// position. Another important difference is that key-types must be
+// copy-constructible.
+
+#ifndef ABSL_CONTAINER_BTREE_MAP_H_
+#define ABSL_CONTAINER_BTREE_MAP_H_
+
+#include "absl/container/internal/btree.h"  // IWYU pragma: export
+#include "absl/container/internal/btree_container.h"  // IWYU pragma: export
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+
+namespace container_internal {
+
+template <typename Key, typename Data, typename Compare, typename Alloc,
+          int TargetNodeSize, bool IsMulti>
+struct map_params;
+
+}  // namespace container_internal
+
+// absl::btree_map<>
+//
+// An `absl::btree_map<K, V>` is an ordered associative container of
+// unique keys and associated values designed to be a more efficient replacement
+// for `std::map` (in most cases).
+//
+// Keys are sorted using an (optional) comparison function, which defaults to
+// `std::less<K>`.
+//
+// An `absl::btree_map<K, V>` uses a default allocator of
+// `std::allocator<std::pair<const K, V>>` to allocate (and deallocate)
+// nodes, and construct and destruct values within those nodes. You may
+// instead specify a custom allocator `A` (which in turn requires specifying a
+// custom comparator `C`) as in `absl::btree_map<K, V, C, A>`.
+//
+template <typename Key, typename Value, typename Compare = std::less<Key>,
+          typename Alloc = std::allocator<std::pair<const Key, Value>>>
+class btree_map
+    : public container_internal::btree_map_container<
+          container_internal::btree<container_internal::map_params<
+              Key, Value, Compare, Alloc, /*TargetNodeSize=*/256,
+              /*IsMulti=*/false>>> {
+  using Base = typename btree_map::btree_map_container;
+
+ public:
+  // Constructors and Assignment Operators
+  //
+  // A `btree_map` supports the same overload set as `std::map`
+  // for construction and assignment:
+  //
+  // * Default constructor
+  //
+  //   absl::btree_map<int, std::string> map1;
+  //
+  // * Initializer List constructor
+  //
+  //   absl::btree_map<int, std::string> map2 =
+  //       {{1, "huey"}, {2, "dewey"}, {3, "louie"},};
+  //
+  // * Copy constructor
+  //
+  //   absl::btree_map<int, std::string> map3(map2);
+  //
+  // * Copy assignment operator
+  //
+  //  absl::btree_map<int, std::string> map4;
+  //  map4 = map3;
+  //
+  // * Move constructor
+  //
+  //   // Move is guaranteed efficient
+  //   absl::btree_map<int, std::string> map5(std::move(map4));
+  //
+  // * Move assignment operator
+  //
+  //   // May be efficient if allocators are compatible
+  //   absl::btree_map<int, std::string> map6;
+  //   map6 = std::move(map5);
+  //
+  // * Range constructor
+  //
+  //   std::vector<std::pair<int, std::string>> v = {{1, "a"}, {2, "b"}};
+  //   absl::btree_map<int, std::string> map7(v.begin(), v.end());
+  btree_map() {}
+  using Base::Base;
+
+  // btree_map::begin()
+  //
+  // Returns an iterator to the beginning of the `btree_map`.
+  using Base::begin;
+
+  // btree_map::cbegin()
+  //
+  // Returns a const iterator to the beginning of the `btree_map`.
+  using Base::cbegin;
+
+  // btree_map::end()
+  //
+  // Returns an iterator to the end of the `btree_map`.
+  using Base::end;
+
+  // btree_map::cend()
+  //
+  // Returns a const iterator to the end of the `btree_map`.
+  using Base::cend;
+
+  // btree_map::empty()
+  //
+  // Returns whether or not the `btree_map` is empty.
+  using Base::empty;
+
+  // btree_map::max_size()
+  //
+  // Returns the largest theoretical possible number of elements within a
+  // `btree_map` under current memory constraints. This value can be thought
+  // of as the largest value of `std::distance(begin(), end())` for a
+  // `btree_map<Key, T>`.
+  using Base::max_size;
+
+  // btree_map::size()
+  //
+  // Returns the number of elements currently within the `btree_map`.
+  using Base::size;
+
+  // btree_map::clear()
+  //
+  // Removes all elements from the `btree_map`. Invalidates any references,
+  // pointers, or iterators referring to contained elements.
+  using Base::clear;
+
+  // btree_map::erase()
+  //
+  // Erases elements within the `btree_map`. If an erase occurs, any references,
+  // pointers, or iterators are invalidated.
+  // Overloads are listed below.
+  //
+  // iterator erase(iterator position):
+  // iterator erase(const_iterator position):
+  //
+  //   Erases the element at `position` of the `btree_map`, returning
+  //   the iterator pointing to the element after the one that was erased
+  //   (or end() if none exists).
+  //
+  // iterator erase(const_iterator first, const_iterator last):
+  //
+  //   Erases the elements in the open interval [`first`, `last`), returning
+  //   the iterator pointing to the element after the interval that was erased
+  //   (or end() if none exists).
+  //
+  // template <typename K> size_type erase(const K& key):
+  //
+  //   Erases the element with the matching key, if it exists, returning the
+  //   number of elements erased (0 or 1).
+  using Base::erase;
+
+  // btree_map::insert()
+  //
+  // Inserts an element of the specified value into the `btree_map`,
+  // returning an iterator pointing to the newly inserted element, provided that
+  // an element with the given key does not already exist. If an insertion
+  // occurs, any references, pointers, or iterators are invalidated.
+  // Overloads are listed below.
+  //
+  // std::pair<iterator,bool> insert(const value_type& value):
+  //
+  //   Inserts a value into the `btree_map`. Returns a pair consisting of an
+  //   iterator to the inserted element (or to the element that prevented the
+  //   insertion) and a bool denoting whether the insertion took place.
+  //
+  // std::pair<iterator,bool> insert(value_type&& value):
+  //
+  //   Inserts a moveable value into the `btree_map`. Returns a pair
+  //   consisting of an iterator to the inserted element (or to the element that
+  //   prevented the insertion) and a bool denoting whether the insertion took
+  //   place.
+  //
+  // iterator insert(const_iterator hint, const value_type& value):
+  // iterator insert(const_iterator hint, value_type&& value):
+  //
+  //   Inserts a value, using the position of `hint` as a non-binding suggestion
+  //   for where to begin the insertion search. Returns an iterator to the
+  //   inserted element, or to the existing element that prevented the
+  //   insertion.
+  //
+  // void insert(InputIterator first, InputIterator last):
+  //
+  //   Inserts a range of values [`first`, `last`).
+  //
+  // void insert(std::initializer_list<init_type> ilist):
+  //
+  //   Inserts the elements within the initializer list `ilist`.
+  using Base::insert;
+
+  // btree_map::insert_or_assign()
+  //
+  // Inserts an element of the specified value into the `btree_map` provided
+  // that a value with the given key does not already exist, or replaces the
+  // corresponding mapped type with the forwarded `obj` argument if a key for
+  // that value already exists, returning an iterator pointing to the newly
+  // inserted element. Overloads are listed below.
+  //
+  // pair<iterator, bool> insert_or_assign(const key_type& k, M&& obj):
+  // pair<iterator, bool> insert_or_assign(key_type&& k, M&& obj):
+  //
+  //   Inserts/Assigns (or moves) the element of the specified key into the
+  //   `btree_map`. If the returned bool is true, insertion took place, and if
+  //   it's false, assignment took place.
+  //
+  // iterator insert_or_assign(const_iterator hint,
+  //                           const key_type& k, M&& obj):
+  // iterator insert_or_assign(const_iterator hint, key_type&& k, M&& obj):
+  //
+  //   Inserts/Assigns (or moves) the element of the specified key into the
+  //   `btree_map` using the position of `hint` as a non-binding suggestion
+  //   for where to begin the insertion search.
+  using Base::insert_or_assign;
+
+  // btree_map::emplace()
+  //
+  // Inserts an element of the specified value by constructing it in-place
+  // within the `btree_map`, provided that no element with the given key
+  // already exists.
+  //
+  // The element may be constructed even if there already is an element with the
+  // key in the container, in which case the newly constructed element will be
+  // destroyed immediately. Prefer `try_emplace()` unless your key is not
+  // copyable or moveable.
+  //
+  // If an insertion occurs, any references, pointers, or iterators are
+  // invalidated.
+  using Base::emplace;
+
+  // btree_map::emplace_hint()
+  //
+  // Inserts an element of the specified value by constructing it in-place
+  // within the `btree_map`, using the position of `hint` as a non-binding
+  // suggestion for where to begin the insertion search, and only inserts
+  // provided that no element with the given key already exists.
+  //
+  // The element may be constructed even if there already is an element with the
+  // key in the container, in which case the newly constructed element will be
+  // destroyed immediately. Prefer `try_emplace()` unless your key is not
+  // copyable or moveable.
+  //
+  // If an insertion occurs, any references, pointers, or iterators are
+  // invalidated.
+  using Base::emplace_hint;
+
+  // btree_map::try_emplace()
+  //
+  // Inserts an element of the specified value by constructing it in-place
+  // within the `btree_map`, provided that no element with the given key
+  // already exists. Unlike `emplace()`, if an element with the given key
+  // already exists, we guarantee that no element is constructed.
+  //
+  // If an insertion occurs, any references, pointers, or iterators are
+  // invalidated.
+  //
+  // Overloads are listed below.
+  //
+  //   std::pair<iterator, bool> try_emplace(const key_type& k, Args&&... args):
+  //   std::pair<iterator, bool> try_emplace(key_type&& k, Args&&... args):
+  //
+  // Inserts (via copy or move) the element of the specified key into the
+  // `btree_map`.
+  //
+  //   iterator try_emplace(const_iterator hint,
+  //                        const key_type& k, Args&&... args):
+  //   iterator try_emplace(const_iterator hint, key_type&& k, Args&&... args):
+  //
+  // Inserts (via copy or move) the element of the specified key into the
+  // `btree_map` using the position of `hint` as a non-binding suggestion
+  // for where to begin the insertion search.
+  using Base::try_emplace;
+
+  // btree_map::extract()
+  //
+  // Extracts the indicated element, erasing it in the process, and returns it
+  // as a C++17-compatible node handle. Overloads are listed below.
+  //
+  // node_type extract(const_iterator position):
+  //
+  //   Extracts the element at the indicated position and returns a node handle
+  //   owning that extracted data.
+  //
+  // template <typename K> node_type extract(const K& k):
+  //
+  //   Extracts the element with the key matching the passed key value and
+  //   returns a node handle owning that extracted data. If the `btree_map`
+  //   does not contain an element with a matching key, this function returns an
+  //   empty node handle.
+  //
+  // NOTE: when compiled in an earlier version of C++ than C++17,
+  // `node_type::key()` returns a const reference to the key instead of a
+  // mutable reference. We cannot safely return a mutable reference without
+  // std::launder (which is not available before C++17).
+  //
+  // NOTE: In this context, `node_type` refers to the C++17 concept of a
+  // move-only type that owns and provides access to the elements in associative
+  // containers (https://en.cppreference.com/w/cpp/container/node_handle).
+  // It does NOT refer to the data layout of the underlying btree.
+  using Base::extract;
+
+  // btree_map::merge()
+  //
+  // Extracts elements from a given `source` btree_map into this
+  // `btree_map`. If the destination `btree_map` already contains an
+  // element with an equivalent key, that element is not extracted.
+  using Base::merge;
+
+  // btree_map::swap(btree_map& other)
+  //
+  // Exchanges the contents of this `btree_map` with those of the `other`
+  // btree_map, avoiding invocation of any move, copy, or swap operations on
+  // individual elements.
+  //
+  // All iterators and references on the `btree_map` remain valid, excepting
+  // for the past-the-end iterator, which is invalidated.
+  using Base::swap;
+
+  // btree_map::at()
+  //
+  // Returns a reference to the mapped value of the element with key equivalent
+  // to the passed key.
+  using Base::at;
+
+  // btree_map::contains()
+  //
+  // template <typename K> bool contains(const K& key) const:
+  //
+  // Determines whether an element comparing equal to the given `key` exists
+  // within the `btree_map`, returning `true` if so or `false` otherwise.
+  //
+  // Supports heterogeneous lookup, provided that the map has a compatible
+  // heterogeneous comparator.
+  using Base::contains;
+
+  // btree_map::count()
+  //
+  // template <typename K> size_type count(const K& key) const:
+  //
+  // Returns the number of elements comparing equal to the given `key` within
+  // the `btree_map`. Note that this function will return either `1` or `0`
+  // since duplicate elements are not allowed within a `btree_map`.
+  //
+  // Supports heterogeneous lookup, provided that the map has a compatible
+  // heterogeneous comparator.
+  using Base::count;
+
+  // btree_map::equal_range()
+  //
+  // Returns a half-open range [first, last), defined by a `std::pair` of two
+  // iterators, containing all elements with the passed key in the `btree_map`.
+  using Base::equal_range;
+
+  // btree_map::find()
+  //
+  // template <typename K> iterator find(const K& key):
+  // template <typename K> const_iterator find(const K& key) const:
+  //
+  // Finds an element with the passed `key` within the `btree_map`.
+  //
+  // Supports heterogeneous lookup, provided that the map has a compatible
+  // heterogeneous comparator.
+  using Base::find;
+
+  // btree_map::lower_bound()
+  //
+  // template <typename K> iterator lower_bound(const K& key):
+  // template <typename K> const_iterator lower_bound(const K& key) const:
+  //
+  // Finds the first element with a key that is not less than `key` within the
+  // `btree_map`.
+  //
+  // Supports heterogeneous lookup, provided that the map has a compatible
+  // heterogeneous comparator.
+  using Base::lower_bound;
+
+  // btree_map::upper_bound()
+  //
+  // template <typename K> iterator upper_bound(const K& key):
+  // template <typename K> const_iterator upper_bound(const K& key) const:
+  //
+  // Finds the first element with a key that is greater than `key` within the
+  // `btree_map`.
+  //
+  // Supports heterogeneous lookup, provided that the map has a compatible
+  // heterogeneous comparator.
+  using Base::upper_bound;
+
+  // btree_map::operator[]()
+  //
+  // Returns a reference to the value mapped to the passed key within the
+  // `btree_map`, performing an `insert()` if the key does not already
+  // exist.
+  //
+  // If an insertion occurs, any references, pointers, or iterators are
+  // invalidated. Otherwise iterators are not affected and references are not
+  // invalidated. Overloads are listed below.
+  //
+  // T& operator[](key_type&& key):
+  // T& operator[](const key_type& key):
+  //
+  //   Inserts a value_type object constructed in-place if the element with the
+  //   given key does not exist.
+  using Base::operator[];
+
+  // btree_map::get_allocator()
+  //
+  // Returns the allocator function associated with this `btree_map`.
+  using Base::get_allocator;
+
+  // btree_map::key_comp();
+  //
+  // Returns the key comparator associated with this `btree_map`.
+  using Base::key_comp;
+
+  // btree_map::value_comp();
+  //
+  // Returns the value comparator associated with this `btree_map`.
+  using Base::value_comp;
+};
+
+// absl::swap(absl::btree_map<>, absl::btree_map<>)
+//
+// Swaps the contents of two `absl::btree_map` containers.
+template <typename K, typename V, typename C, typename A>
+void swap(btree_map<K, V, C, A> &x, btree_map<K, V, C, A> &y) {
+  return x.swap(y);
+}
+
+// absl::erase_if(absl::btree_map<>, Pred)
+//
+// Erases all elements that satisfy the predicate pred from the container.
+// Returns the number of erased elements.
+template <typename K, typename V, typename C, typename A, typename Pred>
+typename btree_map<K, V, C, A>::size_type erase_if(
+    btree_map<K, V, C, A> &map, Pred pred) {
+  return container_internal::btree_access::erase_if(map, std::move(pred));
+}
+
+// absl::btree_multimap
+//
+// An `absl::btree_multimap<K, V>` is an ordered associative container of
+// keys and associated values designed to be a more efficient replacement for
+// `std::multimap` (in most cases). Unlike `absl::btree_map`, a B-tree multimap
+// allows multiple elements with equivalent keys.
+//
+// Keys are sorted using an (optional) comparison function, which defaults to
+// `std::less<K>`.
+//
+// An `absl::btree_multimap<K, V>` uses a default allocator of
+// `std::allocator<std::pair<const K, V>>` to allocate (and deallocate)
+// nodes, and construct and destruct values within those nodes. You may
+// instead specify a custom allocator `A` (which in turn requires specifying a
+// custom comparator `C`) as in `absl::btree_multimap<K, V, C, A>`.
+//
+template <typename Key, typename Value, typename Compare = std::less<Key>,
+          typename Alloc = std::allocator<std::pair<const Key, Value>>>
+class btree_multimap
+    : public container_internal::btree_multimap_container<
+          container_internal::btree<container_internal::map_params<
+              Key, Value, Compare, Alloc, /*TargetNodeSize=*/256,
+              /*IsMulti=*/true>>> {
+  using Base = typename btree_multimap::btree_multimap_container;
+
+ public:
+  // Constructors and Assignment Operators
+  //
+  // A `btree_multimap` supports the same overload set as `std::multimap`
+  // for construction and assignment:
+  //
+  // * Default constructor
+  //
+  //   absl::btree_multimap<int, std::string> map1;
+  //
+  // * Initializer List constructor
+  //
+  //   absl::btree_multimap<int, std::string> map2 =
+  //       {{1, "huey"}, {2, "dewey"}, {3, "louie"},};
+  //
+  // * Copy constructor
+  //
+  //   absl::btree_multimap<int, std::string> map3(map2);
+  //
+  // * Copy assignment operator
+  //
+  //  absl::btree_multimap<int, std::string> map4;
+  //  map4 = map3;
+  //
+  // * Move constructor
+  //
+  //   // Move is guaranteed efficient
+  //   absl::btree_multimap<int, std::string> map5(std::move(map4));
+  //
+  // * Move assignment operator
+  //
+  //   // May be efficient if allocators are compatible
+  //   absl::btree_multimap<int, std::string> map6;
+  //   map6 = std::move(map5);
+  //
+  // * Range constructor
+  //
+  //   std::vector<std::pair<int, std::string>> v = {{1, "a"}, {2, "b"}};
+  //   absl::btree_multimap<int, std::string> map7(v.begin(), v.end());
+  btree_multimap() {}
+  using Base::Base;
+
+  // btree_multimap::begin()
+  //
+  // Returns an iterator to the beginning of the `btree_multimap`.
+  using Base::begin;
+
+  // btree_multimap::cbegin()
+  //
+  // Returns a const iterator to the beginning of the `btree_multimap`.
+  using Base::cbegin;
+
+  // btree_multimap::end()
+  //
+  // Returns an iterator to the end of the `btree_multimap`.
+  using Base::end;
+
+  // btree_multimap::cend()
+  //
+  // Returns a const iterator to the end of the `btree_multimap`.
+  using Base::cend;
+
+  // btree_multimap::empty()
+  //
+  // Returns whether or not the `btree_multimap` is empty.
+  using Base::empty;
+
+  // btree_multimap::max_size()
+  //
+  // Returns the largest theoretical possible number of elements within a
+  // `btree_multimap` under current memory constraints. This value can be
+  // thought of as the largest value of `std::distance(begin(), end())` for a
+  // `btree_multimap<Key, T>`.
+  using Base::max_size;
+
+  // btree_multimap::size()
+  //
+  // Returns the number of elements currently within the `btree_multimap`.
+  using Base::size;
+
+  // btree_multimap::clear()
+  //
+  // Removes all elements from the `btree_multimap`. Invalidates any references,
+  // pointers, or iterators referring to contained elements.
+  using Base::clear;
+
+  // btree_multimap::erase()
+  //
+  // Erases elements within the `btree_multimap`. If an erase occurs, any
+  // references, pointers, or iterators are invalidated.
+  // Overloads are listed below.
+  //
+  // iterator erase(iterator position):
+  // iterator erase(const_iterator position):
+  //
+  //   Erases the element at `position` of the `btree_multimap`, returning
+  //   the iterator pointing to the element after the one that was erased
+  //   (or end() if none exists).
+  //
+  // iterator erase(const_iterator first, const_iterator last):
+  //
+  //   Erases the elements in the open interval [`first`, `last`), returning
+  //   the iterator pointing to the element after the interval that was erased
+  //   (or end() if none exists).
+  //
+  // template <typename K> size_type erase(const K& key):
+  //
+  //   Erases the elements matching the key, if any exist, returning the
+  //   number of elements erased.
+  using Base::erase;
+
+  // btree_multimap::insert()
+  //
+  // Inserts an element of the specified value into the `btree_multimap`,
+  // returning an iterator pointing to the newly inserted element.
+  // Any references, pointers, or iterators are invalidated.  Overloads are
+  // listed below.
+  //
+  // iterator insert(const value_type& value):
+  //
+  //   Inserts a value into the `btree_multimap`, returning an iterator to the
+  //   inserted element.
+  //
+  // iterator insert(value_type&& value):
+  //
+  //   Inserts a moveable value into the `btree_multimap`, returning an iterator
+  //   to the inserted element.
+  //
+  // iterator insert(const_iterator hint, const value_type& value):
+  // iterator insert(const_iterator hint, value_type&& value):
+  //
+  //   Inserts a value, using the position of `hint` as a non-binding suggestion
+  //   for where to begin the insertion search. Returns an iterator to the
+  //   inserted element.
+  //
+  // void insert(InputIterator first, InputIterator last):
+  //
+  //   Inserts a range of values [`first`, `last`).
+  //
+  // void insert(std::initializer_list<init_type> ilist):
+  //
+  //   Inserts the elements within the initializer list `ilist`.
+  using Base::insert;
+
+  // btree_multimap::emplace()
+  //
+  // Inserts an element of the specified value by constructing it in-place
+  // within the `btree_multimap`. Any references, pointers, or iterators are
+  // invalidated.
+  using Base::emplace;
+
+  // btree_multimap::emplace_hint()
+  //
+  // Inserts an element of the specified value by constructing it in-place
+  // within the `btree_multimap`, using the position of `hint` as a non-binding
+  // suggestion for where to begin the insertion search.
+  //
+  // Any references, pointers, or iterators are invalidated.
+  using Base::emplace_hint;
+
+  // btree_multimap::extract()
+  //
+  // Extracts the indicated element, erasing it in the process, and returns it
+  // as a C++17-compatible node handle. Overloads are listed below.
+  //
+  // node_type extract(const_iterator position):
+  //
+  //   Extracts the element at the indicated position and returns a node handle
+  //   owning that extracted data.
+  //
+  // template <typename K> node_type extract(const K& k):
+  //
+  //   Extracts the element with the key matching the passed key value and
+  //   returns a node handle owning that extracted data. If the `btree_multimap`
+  //   does not contain an element with a matching key, this function returns an
+  //   empty node handle.
+  //
+  // NOTE: when compiled in an earlier version of C++ than C++17,
+  // `node_type::key()` returns a const reference to the key instead of a
+  // mutable reference. We cannot safely return a mutable reference without
+  // std::launder (which is not available before C++17).
+  //
+  // NOTE: In this context, `node_type` refers to the C++17 concept of a
+  // move-only type that owns and provides access to the elements in associative
+  // containers (https://en.cppreference.com/w/cpp/container/node_handle).
+  // It does NOT refer to the data layout of the underlying btree.
+  using Base::extract;
+
+  // btree_multimap::merge()
+  //
+  // Extracts all elements from a given `source` btree_multimap into this
+  // `btree_multimap`.
+  using Base::merge;
+
+  // btree_multimap::swap(btree_multimap& other)
+  //
+  // Exchanges the contents of this `btree_multimap` with those of the `other`
+  // btree_multimap, avoiding invocation of any move, copy, or swap operations
+  // on individual elements.
+  //
+  // All iterators and references on the `btree_multimap` remain valid,
+  // excepting for the past-the-end iterator, which is invalidated.
+  using Base::swap;
+
+  // btree_multimap::contains()
+  //
+  // template <typename K> bool contains(const K& key) const:
+  //
+  // Determines whether an element comparing equal to the given `key` exists
+  // within the `btree_multimap`, returning `true` if so or `false` otherwise.
+  //
+  // Supports heterogeneous lookup, provided that the map has a compatible
+  // heterogeneous comparator.
+  using Base::contains;
+
+  // btree_multimap::count()
+  //
+  // template <typename K> size_type count(const K& key) const:
+  //
+  // Returns the number of elements comparing equal to the given `key` within
+  // the `btree_multimap`.
+  //
+  // Supports heterogeneous lookup, provided that the map has a compatible
+  // heterogeneous comparator.
+  using Base::count;
+
+  // btree_multimap::equal_range()
+  //
+  // Returns a half-open range [first, last), defined by a `std::pair` of two
+  // iterators, containing all elements with the passed key in the
+  // `btree_multimap`.
+  using Base::equal_range;
+
+  // btree_multimap::find()
+  //
+  // template <typename K> iterator find(const K& key):
+  // template <typename K> const_iterator find(const K& key) const:
+  //
+  // Finds an element with the passed `key` within the `btree_multimap`.
+  //
+  // Supports heterogeneous lookup, provided that the map has a compatible
+  // heterogeneous comparator.
+  using Base::find;
+
+  // btree_multimap::lower_bound()
+  //
+  // template <typename K> iterator lower_bound(const K& key):
+  // template <typename K> const_iterator lower_bound(const K& key) const:
+  //
+  // Finds the first element with a key that is not less than `key` within the
+  // `btree_multimap`.
+  //
+  // Supports heterogeneous lookup, provided that the map has a compatible
+  // heterogeneous comparator.
+  using Base::lower_bound;
+
+  // btree_multimap::upper_bound()
+  //
+  // template <typename K> iterator upper_bound(const K& key):
+  // template <typename K> const_iterator upper_bound(const K& key) const:
+  //
+  // Finds the first element with a key that is greater than `key` within the
+  // `btree_multimap`.
+  //
+  // Supports heterogeneous lookup, provided that the map has a compatible
+  // heterogeneous comparator.
+  using Base::upper_bound;
+
+  // btree_multimap::get_allocator()
+  //
+  // Returns the allocator function associated with this `btree_multimap`.
+  using Base::get_allocator;
+
+  // btree_multimap::key_comp();
+  //
+  // Returns the key comparator associated with this `btree_multimap`.
+  using Base::key_comp;
+
+  // btree_multimap::value_comp();
+  //
+  // Returns the value comparator associated with this `btree_multimap`.
+  using Base::value_comp;
+};
+
+// absl::swap(absl::btree_multimap<>, absl::btree_multimap<>)
+//
+// Swaps the contents of two `absl::btree_multimap` containers.
+template <typename K, typename V, typename C, typename A>
+void swap(btree_multimap<K, V, C, A> &x, btree_multimap<K, V, C, A> &y) {
+  return x.swap(y);
+}
+
+// absl::erase_if(absl::btree_multimap<>, Pred)
+//
+// Erases all elements that satisfy the predicate pred from the container.
+// Returns the number of erased elements.
+template <typename K, typename V, typename C, typename A, typename Pred>
+typename btree_multimap<K, V, C, A>::size_type erase_if(
+    btree_multimap<K, V, C, A> &map, Pred pred) {
+  return container_internal::btree_access::erase_if(map, std::move(pred));
+}
+
+namespace container_internal {
+
+// A parameters structure for holding the type parameters for a btree_map.
+// Compare and Alloc should be nothrow copy-constructible.
+template <typename Key, typename Data, typename Compare, typename Alloc,
+          int TargetNodeSize, bool IsMulti>
+struct map_params : common_params<Key, Compare, Alloc, TargetNodeSize, IsMulti,
+                                  /*IsMap=*/true, map_slot_policy<Key, Data>> {
+  using super_type = typename map_params::common_params;
+  using mapped_type = Data;
+  // This type allows us to move keys when it is safe to do so. It is safe
+  // for maps in which value_type and mutable_value_type are layout compatible.
+  using slot_policy = typename super_type::slot_policy;
+  using slot_type = typename super_type::slot_type;
+  using value_type = typename super_type::value_type;
+  using init_type = typename super_type::init_type;
+
+  template <typename V>
+  static auto key(const V &value) -> decltype(value.first) {
+    return value.first;
+  }
+  static const Key &key(const slot_type *s) { return slot_policy::key(s); }
+  static const Key &key(slot_type *s) { return slot_policy::key(s); }
+  // For use in node handle.
+  static auto mutable_key(slot_type *s)
+      -> decltype(slot_policy::mutable_key(s)) {
+    return slot_policy::mutable_key(s);
+  }
+  static mapped_type &value(value_type *value) { return value->second; }
+};
+
+}  // namespace container_internal
+
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_CONTAINER_BTREE_MAP_H_
--- a/include/absl/container/btree_set.h
+++ b/include/absl/container/btree_set.h
@ -0,0 +1,793 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// -----------------------------------------------------------------------------
+// File: btree_set.h
+// -----------------------------------------------------------------------------
+//
+// This header file defines B-tree sets: sorted associative containers of
+// values.
+//
+//     * `absl::btree_set<>`
+//     * `absl::btree_multiset<>`
+//
+// These B-tree types are similar to the corresponding types in the STL
+// (`std::set` and `std::multiset`) and generally conform to the STL interfaces
+// of those types. However, because they are implemented using B-trees, they
+// are more efficient in most situations.
+//
+// Unlike `std::set` and `std::multiset`, which are commonly implemented using
+// red-black tree nodes, B-tree sets use more generic B-tree nodes able to hold
+// multiple values per node. Holding multiple values per node often makes
+// B-tree sets perform better than their `std::set` counterparts, because
+// multiple entries can be checked within the same cache hit.
+//
+// However, these types should not be considered drop-in replacements for
+// `std::set` and `std::multiset` as there are some API differences, which are
+// noted in this header file. The most consequential differences with respect to
+// migrating to b-tree from the STL types are listed in the next paragraph.
+// Other API differences are minor.
+//
+// Importantly, insertions and deletions may invalidate outstanding iterators,
+// pointers, and references to elements. Such invalidations are typically only
+// an issue if insertion and deletion operations are interleaved with the use of
+// more than one iterator, pointer, or reference simultaneously. For this
+// reason, `insert()` and `erase()` return a valid iterator at the current
+// position.
+
+#ifndef ABSL_CONTAINER_BTREE_SET_H_
+#define ABSL_CONTAINER_BTREE_SET_H_
+
+#include "absl/container/internal/btree.h"  // IWYU pragma: export
+#include "absl/container/internal/btree_container.h"  // IWYU pragma: export
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+
+namespace container_internal {
+
+template <typename Key>
+struct set_slot_policy;
+
+template <typename Key, typename Compare, typename Alloc, int TargetNodeSize,
+          bool IsMulti>
+struct set_params;
+
+}  // namespace container_internal
+
+// absl::btree_set<>
+//
+// An `absl::btree_set<K>` is an ordered associative container of unique key
+// values designed to be a more efficient replacement for `std::set` (in most
+// cases).
+//
+// Keys are sorted using an (optional) comparison function, which defaults to
+// `std::less<K>`.
+//
+// An `absl::btree_set<K>` uses a default allocator of `std::allocator<K>` to
+// allocate (and deallocate) nodes, and construct and destruct values within
+// those nodes. You may instead specify a custom allocator `A` (which in turn
+// requires specifying a custom comparator `C`) as in
+// `absl::btree_set<K, C, A>`.
+//
+template <typename Key, typename Compare = std::less<Key>,
+          typename Alloc = std::allocator<Key>>
+class btree_set
+    : public container_internal::btree_set_container<
+          container_internal::btree<container_internal::set_params<
+              Key, Compare, Alloc, /*TargetNodeSize=*/256,
+              /*IsMulti=*/false>>> {
+  using Base = typename btree_set::btree_set_container;
+
+ public:
+  // Constructors and Assignment Operators
+  //
+  // A `btree_set` supports the same overload set as `std::set`
+  // for construction and assignment:
+  //
+  // * Default constructor
+  //
+  //   absl::btree_set<std::string> set1;
+  //
+  // * Initializer List constructor
+  //
+  //   absl::btree_set<std::string> set2 =
+  //       {{"huey"}, {"dewey"}, {"louie"},};
+  //
+  // * Copy constructor
+  //
+  //   absl::btree_set<std::string> set3(set2);
+  //
+  // * Copy assignment operator
+  //
+  //  absl::btree_set<std::string> set4;
+  //  set4 = set3;
+  //
+  // * Move constructor
+  //
+  //   // Move is guaranteed efficient
+  //   absl::btree_set<std::string> set5(std::move(set4));
+  //
+  // * Move assignment operator
+  //
+  //   // May be efficient if allocators are compatible
+  //   absl::btree_set<std::string> set6;
+  //   set6 = std::move(set5);
+  //
+  // * Range constructor
+  //
+  //   std::vector<std::string> v = {"a", "b"};
+  //   absl::btree_set<std::string> set7(v.begin(), v.end());
+  btree_set() {}
+  using Base::Base;
+
+  // btree_set::begin()
+  //
+  // Returns an iterator to the beginning of the `btree_set`.
+  using Base::begin;
+
+  // btree_set::cbegin()
+  //
+  // Returns a const iterator to the beginning of the `btree_set`.
+  using Base::cbegin;
+
+  // btree_set::end()
+  //
+  // Returns an iterator to the end of the `btree_set`.
+  using Base::end;
+
+  // btree_set::cend()
+  //
+  // Returns a const iterator to the end of the `btree_set`.
+  using Base::cend;
+
+  // btree_set::empty()
+  //
+  // Returns whether or not the `btree_set` is empty.
+  using Base::empty;
+
+  // btree_set::max_size()
+  //
+  // Returns the largest theoretical possible number of elements within a
+  // `btree_set` under current memory constraints. This value can be thought
+  // of as the largest value of `std::distance(begin(), end())` for a
+  // `btree_set<Key>`.
+  using Base::max_size;
+
+  // btree_set::size()
+  //
+  // Returns the number of elements currently within the `btree_set`.
+  using Base::size;
+
+  // btree_set::clear()
+  //
+  // Removes all elements from the `btree_set`. Invalidates any references,
+  // pointers, or iterators referring to contained elements.
+  using Base::clear;
+
+  // btree_set::erase()
+  //
+  // Erases elements within the `btree_set`. Overloads are listed below.
+  //
+  // iterator erase(iterator position):
+  // iterator erase(const_iterator position):
+  //
+  //   Erases the element at `position` of the `btree_set`, returning
+  //   the iterator pointing to the element after the one that was erased
+  //   (or end() if none exists).
+  //
+  // iterator erase(const_iterator first, const_iterator last):
+  //
+  //   Erases the elements in the open interval [`first`, `last`), returning
+  //   the iterator pointing to the element after the interval that was erased
+  //   (or end() if none exists).
+  //
+  // template <typename K> size_type erase(const K& key):
+  //
+  //   Erases the element with the matching key, if it exists, returning the
+  //   number of elements erased (0 or 1).
+  using Base::erase;
+
+  // btree_set::insert()
+  //
+  // Inserts an element of the specified value into the `btree_set`,
+  // returning an iterator pointing to the newly inserted element, provided that
+  // an element with the given key does not already exist. If an insertion
+  // occurs, any references, pointers, or iterators are invalidated.
+  // Overloads are listed below.
+  //
+  // std::pair<iterator,bool> insert(const value_type& value):
+  //
+  //   Inserts a value into the `btree_set`. Returns a pair consisting of an
+  //   iterator to the inserted element (or to the element that prevented the
+  //   insertion) and a bool denoting whether the insertion took place.
+  //
+  // std::pair<iterator,bool> insert(value_type&& value):
+  //
+  //   Inserts a moveable value into the `btree_set`. Returns a pair
+  //   consisting of an iterator to the inserted element (or to the element that
+  //   prevented the insertion) and a bool denoting whether the insertion took
+  //   place.
+  //
+  // iterator insert(const_iterator hint, const value_type& value):
+  // iterator insert(const_iterator hint, value_type&& value):
+  //
+  //   Inserts a value, using the position of `hint` as a non-binding suggestion
+  //   for where to begin the insertion search. Returns an iterator to the
+  //   inserted element, or to the existing element that prevented the
+  //   insertion.
+  //
+  // void insert(InputIterator first, InputIterator last):
+  //
+  //   Inserts a range of values [`first`, `last`).
+  //
+  // void insert(std::initializer_list<init_type> ilist):
+  //
+  //   Inserts the elements within the initializer list `ilist`.
+  using Base::insert;
+
+  // btree_set::emplace()
+  //
+  // Inserts an element of the specified value by constructing it in-place
+  // within the `btree_set`, provided that no element with the given key
+  // already exists.
+  //
+  // The element may be constructed even if there already is an element with the
+  // key in the container, in which case the newly constructed element will be
+  // destroyed immediately.
+  //
+  // If an insertion occurs, any references, pointers, or iterators are
+  // invalidated.
+  using Base::emplace;
+
+  // btree_set::emplace_hint()
+  //
+  // Inserts an element of the specified value by constructing it in-place
+  // within the `btree_set`, using the position of `hint` as a non-binding
+  // suggestion for where to begin the insertion search, and only inserts
+  // provided that no element with the given key already exists.
+  //
+  // The element may be constructed even if there already is an element with the
+  // key in the container, in which case the newly constructed element will be
+  // destroyed immediately.
+  //
+  // If an insertion occurs, any references, pointers, or iterators are
+  // invalidated.
+  using Base::emplace_hint;
+
+  // btree_set::extract()
+  //
+  // Extracts the indicated element, erasing it in the process, and returns it
+  // as a C++17-compatible node handle. Overloads are listed below.
+  //
+  // node_type extract(const_iterator position):
+  //
+  //   Extracts the element at the indicated position and returns a node handle
+  //   owning that extracted data.
+  //
+  // template <typename K> node_type extract(const K& k):
+  //
+  //   Extracts the element with the key matching the passed key value and
+  //   returns a node handle owning that extracted data. If the `btree_set`
+  //   does not contain an element with a matching key, this function returns an
+  //   empty node handle.
+  //
+  // NOTE: In this context, `node_type` refers to the C++17 concept of a
+  // move-only type that owns and provides access to the elements in associative
+  // containers (https://en.cppreference.com/w/cpp/container/node_handle).
+  // It does NOT refer to the data layout of the underlying btree.
+  using Base::extract;
+
+  // btree_set::merge()
+  //
+  // Extracts elements from a given `source` btree_set into this
+  // `btree_set`. If the destination `btree_set` already contains an
+  // element with an equivalent key, that element is not extracted.
+  using Base::merge;
+
+  // btree_set::swap(btree_set& other)
+  //
+  // Exchanges the contents of this `btree_set` with those of the `other`
+  // btree_set, avoiding invocation of any move, copy, or swap operations on
+  // individual elements.
+  //
+  // All iterators and references on the `btree_set` remain valid, excepting
+  // for the past-the-end iterator, which is invalidated.
+  using Base::swap;
+
+  // btree_set::contains()
+  //
+  // template <typename K> bool contains(const K& key) const:
+  //
+  // Determines whether an element comparing equal to the given `key` exists
+  // within the `btree_set`, returning `true` if so or `false` otherwise.
+  //
+  // Supports heterogeneous lookup, provided that the set has a compatible
+  // heterogeneous comparator.
+  using Base::contains;
+
+  // btree_set::count()
+  //
+  // template <typename K> size_type count(const K& key) const:
+  //
+  // Returns the number of elements comparing equal to the given `key` within
+  // the `btree_set`. Note that this function will return either `1` or `0`
+  // since duplicate elements are not allowed within a `btree_set`.
+  //
+  // Supports heterogeneous lookup, provided that the set has a compatible
+  // heterogeneous comparator.
+  using Base::count;
+
+  // btree_set::equal_range()
+  //
+  // Returns a closed range [first, last], defined by a `std::pair` of two
+  // iterators, containing all elements with the passed key in the
+  // `btree_set`.
+  using Base::equal_range;
+
+  // btree_set::find()
+  //
+  // template <typename K> iterator find(const K& key):
+  // template <typename K> const_iterator find(const K& key) const:
+  //
+  // Finds an element with the passed `key` within the `btree_set`.
+  //
+  // Supports heterogeneous lookup, provided that the set has a compatible
+  // heterogeneous comparator.
+  using Base::find;
+
+  // btree_set::lower_bound()
+  //
+  // template <typename K> iterator lower_bound(const K& key):
+  // template <typename K> const_iterator lower_bound(const K& key) const:
+  //
+  // Finds the first element that is not less than `key` within the `btree_set`.
+  //
+  // Supports heterogeneous lookup, provided that the set has a compatible
+  // heterogeneous comparator.
+  using Base::lower_bound;
+
+  // btree_set::upper_bound()
+  //
+  // template <typename K> iterator upper_bound(const K& key):
+  // template <typename K> const_iterator upper_bound(const K& key) const:
+  //
+  // Finds the first element that is greater than `key` within the `btree_set`.
+  //
+  // Supports heterogeneous lookup, provided that the set has a compatible
+  // heterogeneous comparator.
+  using Base::upper_bound;
+
+  // btree_set::get_allocator()
+  //
+  // Returns the allocator function associated with this `btree_set`.
+  using Base::get_allocator;
+
+  // btree_set::key_comp();
+  //
+  // Returns the key comparator associated with this `btree_set`.
+  using Base::key_comp;
+
+  // btree_set::value_comp();
+  //
+  // Returns the value comparator associated with this `btree_set`. The keys to
+  // sort the elements are the values themselves, therefore `value_comp` and its
+  // sibling member function `key_comp` are equivalent.
+  using Base::value_comp;
+};
+
+// absl::swap(absl::btree_set<>, absl::btree_set<>)
+//
+// Swaps the contents of two `absl::btree_set` containers.
+template <typename K, typename C, typename A>
+void swap(btree_set<K, C, A> &x, btree_set<K, C, A> &y) {
+  return x.swap(y);
+}
+
+// absl::erase_if(absl::btree_set<>, Pred)
+//
+// Erases all elements that satisfy the predicate pred from the container.
+// Returns the number of erased elements.
+template <typename K, typename C, typename A, typename Pred>
+typename btree_set<K, C, A>::size_type erase_if(btree_set<K, C, A> &set,
+                                                Pred pred) {
+  return container_internal::btree_access::erase_if(set, std::move(pred));
+}
+
+// absl::btree_multiset<>
+//
+// An `absl::btree_multiset<K>` is an ordered associative container of
+// keys and associated values designed to be a more efficient replacement
+// for `std::multiset` (in most cases). Unlike `absl::btree_set`, a B-tree
+// multiset allows equivalent elements.
+//
+// Keys are sorted using an (optional) comparison function, which defaults to
+// `std::less<K>`.
+//
+// An `absl::btree_multiset<K>` uses a default allocator of `std::allocator<K>`
+// to allocate (and deallocate) nodes, and construct and destruct values within
+// those nodes. You may instead specify a custom allocator `A` (which in turn
+// requires specifying a custom comparator `C`) as in
+// `absl::btree_multiset<K, C, A>`.
+//
+template <typename Key, typename Compare = std::less<Key>,
+          typename Alloc = std::allocator<Key>>
+class btree_multiset
+    : public container_internal::btree_multiset_container<
+          container_internal::btree<container_internal::set_params<
+              Key, Compare, Alloc, /*TargetNodeSize=*/256,
+              /*IsMulti=*/true>>> {
+  using Base = typename btree_multiset::btree_multiset_container;
+
+ public:
+  // Constructors and Assignment Operators
+  //
+  // A `btree_multiset` supports the same overload set as `std::set`
+  // for construction and assignment:
+  //
+  // * Default constructor
+  //
+  //   absl::btree_multiset<std::string> set1;
+  //
+  // * Initializer List constructor
+  //
+  //   absl::btree_multiset<std::string> set2 =
+  //       {{"huey"}, {"dewey"}, {"louie"},};
+  //
+  // * Copy constructor
+  //
+  //   absl::btree_multiset<std::string> set3(set2);
+  //
+  // * Copy assignment operator
+  //
+  //  absl::btree_multiset<std::string> set4;
+  //  set4 = set3;
+  //
+  // * Move constructor
+  //
+  //   // Move is guaranteed efficient
+  //   absl::btree_multiset<std::string> set5(std::move(set4));
+  //
+  // * Move assignment operator
+  //
+  //   // May be efficient if allocators are compatible
+  //   absl::btree_multiset<std::string> set6;
+  //   set6 = std::move(set5);
+  //
+  // * Range constructor
+  //
+  //   std::vector<std::string> v = {"a", "b"};
+  //   absl::btree_multiset<std::string> set7(v.begin(), v.end());
+  btree_multiset() {}
+  using Base::Base;
+
+  // btree_multiset::begin()
+  //
+  // Returns an iterator to the beginning of the `btree_multiset`.
+  using Base::begin;
+
+  // btree_multiset::cbegin()
+  //
+  // Returns a const iterator to the beginning of the `btree_multiset`.
+  using Base::cbegin;
+
+  // btree_multiset::end()
+  //
+  // Returns an iterator to the end of the `btree_multiset`.
+  using Base::end;
+
+  // btree_multiset::cend()
+  //
+  // Returns a const iterator to the end of the `btree_multiset`.
+  using Base::cend;
+
+  // btree_multiset::empty()
+  //
+  // Returns whether or not the `btree_multiset` is empty.
+  using Base::empty;
+
+  // btree_multiset::max_size()
+  //
+  // Returns the largest theoretical possible number of elements within a
+  // `btree_multiset` under current memory constraints. This value can be
+  // thought of as the largest value of `std::distance(begin(), end())` for a
+  // `btree_multiset<Key>`.
+  using Base::max_size;
+
+  // btree_multiset::size()
+  //
+  // Returns the number of elements currently within the `btree_multiset`.
+  using Base::size;
+
+  // btree_multiset::clear()
+  //
+  // Removes all elements from the `btree_multiset`. Invalidates any references,
+  // pointers, or iterators referring to contained elements.
+  using Base::clear;
+
+  // btree_multiset::erase()
+  //
+  // Erases elements within the `btree_multiset`. Overloads are listed below.
+  //
+  // iterator erase(iterator position):
+  // iterator erase(const_iterator position):
+  //
+  //   Erases the element at `position` of the `btree_multiset`, returning
+  //   the iterator pointing to the element after the one that was erased
+  //   (or end() if none exists).
+  //
+  // iterator erase(const_iterator first, const_iterator last):
+  //
+  //   Erases the elements in the open interval [`first`, `last`), returning
+  //   the iterator pointing to the element after the interval that was erased
+  //   (or end() if none exists).
+  //
+  // template <typename K> size_type erase(const K& key):
+  //
+  //   Erases the elements matching the key, if any exist, returning the
+  //   number of elements erased.
+  using Base::erase;
+
+  // btree_multiset::insert()
+  //
+  // Inserts an element of the specified value into the `btree_multiset`,
+  // returning an iterator pointing to the newly inserted element.
+  // Any references, pointers, or iterators are invalidated.  Overloads are
+  // listed below.
+  //
+  // iterator insert(const value_type& value):
+  //
+  //   Inserts a value into the `btree_multiset`, returning an iterator to the
+  //   inserted element.
+  //
+  // iterator insert(value_type&& value):
+  //
+  //   Inserts a moveable value into the `btree_multiset`, returning an iterator
+  //   to the inserted element.
+  //
+  // iterator insert(const_iterator hint, const value_type& value):
+  // iterator insert(const_iterator hint, value_type&& value):
+  //
+  //   Inserts a value, using the position of `hint` as a non-binding suggestion
+  //   for where to begin the insertion search. Returns an iterator to the
+  //   inserted element.
+  //
+  // void insert(InputIterator first, InputIterator last):
+  //
+  //   Inserts a range of values [`first`, `last`).
+  //
+  // void insert(std::initializer_list<init_type> ilist):
+  //
+  //   Inserts the elements within the initializer list `ilist`.
+  using Base::insert;
+
+  // btree_multiset::emplace()
+  //
+  // Inserts an element of the specified value by constructing it in-place
+  // within the `btree_multiset`. Any references, pointers, or iterators are
+  // invalidated.
+  using Base::emplace;
+
+  // btree_multiset::emplace_hint()
+  //
+  // Inserts an element of the specified value by constructing it in-place
+  // within the `btree_multiset`, using the position of `hint` as a non-binding
+  // suggestion for where to begin the insertion search.
+  //
+  // Any references, pointers, or iterators are invalidated.
+  using Base::emplace_hint;
+
+  // btree_multiset::extract()
+  //
+  // Extracts the indicated element, erasing it in the process, and returns it
+  // as a C++17-compatible node handle. Overloads are listed below.
+  //
+  // node_type extract(const_iterator position):
+  //
+  //   Extracts the element at the indicated position and returns a node handle
+  //   owning that extracted data.
+  //
+  // template <typename K> node_type extract(const K& k):
+  //
+  //   Extracts the element with the key matching the passed key value and
+  //   returns a node handle owning that extracted data. If the `btree_multiset`
+  //   does not contain an element with a matching key, this function returns an
+  //   empty node handle.
+  //
+  // NOTE: In this context, `node_type` refers to the C++17 concept of a
+  // move-only type that owns and provides access to the elements in associative
+  // containers (https://en.cppreference.com/w/cpp/container/node_handle).
+  // It does NOT refer to the data layout of the underlying btree.
+  using Base::extract;
+
+  // btree_multiset::merge()
+  //
+  // Extracts all elements from a given `source` btree_multiset into this
+  // `btree_multiset`.
+  using Base::merge;
+
+  // btree_multiset::swap(btree_multiset& other)
+  //
+  // Exchanges the contents of this `btree_multiset` with those of the `other`
+  // btree_multiset, avoiding invocation of any move, copy, or swap operations
+  // on individual elements.
+  //
+  // All iterators and references on the `btree_multiset` remain valid,
+  // excepting for the past-the-end iterator, which is invalidated.
+  using Base::swap;
+
+  // btree_multiset::contains()
+  //
+  // template <typename K> bool contains(const K& key) const:
+  //
+  // Determines whether an element comparing equal to the given `key` exists
+  // within the `btree_multiset`, returning `true` if so or `false` otherwise.
+  //
+  // Supports heterogeneous lookup, provided that the set has a compatible
+  // heterogeneous comparator.
+  using Base::contains;
+
+  // btree_multiset::count()
+  //
+  // template <typename K> size_type count(const K& key) const:
+  //
+  // Returns the number of elements comparing equal to the given `key` within
+  // the `btree_multiset`.
+  //
+  // Supports heterogeneous lookup, provided that the set has a compatible
+  // heterogeneous comparator.
+  using Base::count;
+
+  // btree_multiset::equal_range()
+  //
+  // Returns a closed range [first, last], defined by a `std::pair` of two
+  // iterators, containing all elements with the passed key in the
+  // `btree_multiset`.
+  using Base::equal_range;
+
+  // btree_multiset::find()
+  //
+  // template <typename K> iterator find(const K& key):
+  // template <typename K> const_iterator find(const K& key) const:
+  //
+  // Finds an element with the passed `key` within the `btree_multiset`.
+  //
+  // Supports heterogeneous lookup, provided that the set has a compatible
+  // heterogeneous comparator.
+  using Base::find;
+
+  // btree_multiset::lower_bound()
+  //
+  // template <typename K> iterator lower_bound(const K& key):
+  // template <typename K> const_iterator lower_bound(const K& key) const:
+  //
+  // Finds the first element that is not less than `key` within the
+  // `btree_multiset`.
+  //
+  // Supports heterogeneous lookup, provided that the set has a compatible
+  // heterogeneous comparator.
+  using Base::lower_bound;
+
+  // btree_multiset::upper_bound()
+  //
+  // template <typename K> iterator upper_bound(const K& key):
+  // template <typename K> const_iterator upper_bound(const K& key) const:
+  //
+  // Finds the first element that is greater than `key` within the
+  // `btree_multiset`.
+  //
+  // Supports heterogeneous lookup, provided that the set has a compatible
+  // heterogeneous comparator.
+  using Base::upper_bound;
+
+  // btree_multiset::get_allocator()
+  //
+  // Returns the allocator function associated with this `btree_multiset`.
+  using Base::get_allocator;
+
+  // btree_multiset::key_comp();
+  //
+  // Returns the key comparator associated with this `btree_multiset`.
+  using Base::key_comp;
+
+  // btree_multiset::value_comp();
+  //
+  // Returns the value comparator associated with this `btree_multiset`. The
+  // keys to sort the elements are the values themselves, therefore `value_comp`
+  // and its sibling member function `key_comp` are equivalent.
+  using Base::value_comp;
+};
+
+// absl::swap(absl::btree_multiset<>, absl::btree_multiset<>)
+//
+// Swaps the contents of two `absl::btree_multiset` containers.
+template <typename K, typename C, typename A>
+void swap(btree_multiset<K, C, A> &x, btree_multiset<K, C, A> &y) {
+  return x.swap(y);
+}
+
+// absl::erase_if(absl::btree_multiset<>, Pred)
+//
+// Erases all elements that satisfy the predicate pred from the container.
+// Returns the number of erased elements.
+template <typename K, typename C, typename A, typename Pred>
+typename btree_multiset<K, C, A>::size_type erase_if(
+   btree_multiset<K, C, A> & set, Pred pred) {
+  return container_internal::btree_access::erase_if(set, std::move(pred));
+}
+
+namespace container_internal {
+
+// This type implements the necessary functions from the
+// absl::container_internal::slot_type interface for btree_(multi)set.
+template <typename Key>
+struct set_slot_policy {
+  using slot_type = Key;
+  using value_type = Key;
+  using mutable_value_type = Key;
+
+  static value_type &element(slot_type *slot) { return *slot; }
+  static const value_type &element(const slot_type *slot) { return *slot; }
+
+  template <typename Alloc, class... Args>
+  static void construct(Alloc *alloc, slot_type *slot, Args &&...args) {
+    absl::allocator_traits<Alloc>::construct(*alloc, slot,
+                                             std::forward<Args>(args)...);
+  }
+
+  template <typename Alloc>
+  static void construct(Alloc *alloc, slot_type *slot, slot_type *other) {
+    absl::allocator_traits<Alloc>::construct(*alloc, slot, std::move(*other));
+  }
+
+  template <typename Alloc>
+  static void construct(Alloc *alloc, slot_type *slot, const slot_type *other) {
+    absl::allocator_traits<Alloc>::construct(*alloc, slot, *other);
+  }
+
+  template <typename Alloc>
+  static void destroy(Alloc *alloc, slot_type *slot) {
+    absl::allocator_traits<Alloc>::destroy(*alloc, slot);
+  }
+
+  template <typename Alloc>
+  static void transfer(Alloc *alloc, slot_type *new_slot, slot_type *old_slot) {
+    construct(alloc, new_slot, old_slot);
+    destroy(alloc, old_slot);
+  }
+};
+
+// A parameters structure for holding the type parameters for a btree_set.
+// Compare and Alloc should be nothrow copy-constructible.
+template <typename Key, typename Compare, typename Alloc, int TargetNodeSize,
+          bool IsMulti>
+struct set_params : common_params<Key, Compare, Alloc, TargetNodeSize, IsMulti,
+                                  /*IsMap=*/false, set_slot_policy<Key>> {
+  using value_type = Key;
+  using slot_type = typename set_params::common_params::slot_type;
+
+  template <typename V>
+  static const V &key(const V &value) {
+    return value;
+  }
+  static const Key &key(const slot_type *slot) { return *slot; }
+  static const Key &key(slot_type *slot) { return *slot; }
+};
+
+}  // namespace container_internal
+
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_CONTAINER_BTREE_SET_H_
--- a/include/absl/container/btree_test.h
+++ b/include/absl/container/btree_test.h
@ -0,0 +1,166 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef ABSL_CONTAINER_BTREE_TEST_H_
+#define ABSL_CONTAINER_BTREE_TEST_H_
+
+#include <algorithm>
+#include <cassert>
+#include <random>
+#include <string>
+#include <utility>
+#include <vector>
+
+#include "absl/container/btree_map.h"
+#include "absl/container/btree_set.h"
+#include "absl/container/flat_hash_set.h"
+#include "absl/strings/cord.h"
+#include "absl/time/time.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace container_internal {
+
+// Like remove_const but propagates the removal through std::pair.
+template <typename T>
+struct remove_pair_const {
+  using type = typename std::remove_const<T>::type;
+};
+template <typename T, typename U>
+struct remove_pair_const<std::pair<T, U> > {
+  using type = std::pair<typename remove_pair_const<T>::type,
+                         typename remove_pair_const<U>::type>;
+};
+
+// Utility class to provide an accessor for a key given a value. The default
+// behavior is to treat the value as a pair and return the first element.
+template <typename K, typename V>
+struct KeyOfValue {
+  struct type {
+    const K& operator()(const V& p) const { return p.first; }
+  };
+};
+
+// Partial specialization of KeyOfValue class for when the key and value are
+// the same type such as in set<> and btree_set<>.
+template <typename K>
+struct KeyOfValue<K, K> {
+  struct type {
+    const K& operator()(const K& k) const { return k; }
+  };
+};
+
+inline char* GenerateDigits(char buf[16], unsigned val, unsigned maxval) {
+  assert(val <= maxval);
+  constexpr unsigned kBase = 64;  // avoid integer division.
+  unsigned p = 15;
+  buf[p--] = 0;
+  while (maxval > 0) {
+    buf[p--] = ' ' + (val % kBase);
+    val /= kBase;
+    maxval /= kBase;
+  }
+  return buf + p + 1;
+}
+
+template <typename K>
+struct Generator {
+  int maxval;
+  explicit Generator(int m) : maxval(m) {}
+  K operator()(int i) const {
+    assert(i <= maxval);
+    return K(i);
+  }
+};
+
+template <>
+struct Generator<absl::Time> {
+  int maxval;
+  explicit Generator(int m) : maxval(m) {}
+  absl::Time operator()(int i) const { return absl::FromUnixMillis(i); }
+};
+
+template <>
+struct Generator<std::string> {
+  int maxval;
+  explicit Generator(int m) : maxval(m) {}
+  std::string operator()(int i) const {
+    char buf[16];
+    return GenerateDigits(buf, i, maxval);
+  }
+};
+
+template <>
+struct Generator<Cord> {
+  int maxval;
+  explicit Generator(int m) : maxval(m) {}
+  Cord operator()(int i) const {
+    char buf[16];
+    return Cord(GenerateDigits(buf, i, maxval));
+  }
+};
+
+template <typename T, typename U>
+struct Generator<std::pair<T, U> > {
+  Generator<typename remove_pair_const<T>::type> tgen;
+  Generator<typename remove_pair_const<U>::type> ugen;
+
+  explicit Generator(int m) : tgen(m), ugen(m) {}
+  std::pair<T, U> operator()(int i) const {
+    return std::make_pair(tgen(i), ugen(i));
+  }
+};
+
+// Generate n values for our tests and benchmarks. Value range is [0, maxval].
+inline std::vector<int> GenerateNumbersWithSeed(int n, int maxval, int seed) {
+  // NOTE: Some tests rely on generated numbers not changing between test runs.
+  // We use std::minstd_rand0 because it is well-defined, but don't use
+  // std::uniform_int_distribution because platforms use different algorithms.
+  std::minstd_rand0 rng(seed);
+
+  std::vector<int> values;
+  absl::flat_hash_set<int> unique_values;
+  if (values.size() < n) {
+    for (int i = values.size(); i < n; i++) {
+      int value;
+      do {
+        value = static_cast<int>(rng()) % (maxval + 1);
+      } while (!unique_values.insert(value).second);
+
+      values.push_back(value);
+    }
+  }
+  return values;
+}
+
+// Generates n values in the range [0, maxval].
+template <typename V>
+std::vector<V> GenerateValuesWithSeed(int n, int maxval, int seed) {
+  const std::vector<int> nums = GenerateNumbersWithSeed(n, maxval, seed);
+  Generator<V> gen(maxval);
+  std::vector<V> vec;
+
+  vec.reserve(n);
+  for (int i = 0; i < n; i++) {
+    vec.push_back(gen(nums[i]));
+  }
+
+  return vec;
+}
+
+}  // namespace container_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_CONTAINER_BTREE_TEST_H_
--- a/include/absl/container/fixed_array.h
+++ b/include/absl/container/fixed_array.h
@ -0,0 +1,529 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// -----------------------------------------------------------------------------
+// File: fixed_array.h
+// -----------------------------------------------------------------------------
+//
+// A `FixedArray<T>` represents a non-resizable array of `T` where the length of
+// the array can be determined at run-time. It is a good replacement for
+// non-standard and deprecated uses of `alloca()` and variable length arrays
+// within the GCC extension. (See
+// https://gcc.gnu.org/onlinedocs/gcc/Variable-Length.html).
+//
+// `FixedArray` allocates small arrays inline, keeping performance fast by
+// avoiding heap operations. It also helps reduce the chances of
+// accidentally overflowing your stack if large input is passed to
+// your function.
+
+#ifndef ABSL_CONTAINER_FIXED_ARRAY_H_
+#define ABSL_CONTAINER_FIXED_ARRAY_H_
+
+#include <algorithm>
+#include <cassert>
+#include <cstddef>
+#include <initializer_list>
+#include <iterator>
+#include <limits>
+#include <memory>
+#include <new>
+#include <type_traits>
+
+#include "absl/algorithm/algorithm.h"
+#include "absl/base/config.h"
+#include "absl/base/dynamic_annotations.h"
+#include "absl/base/internal/throw_delegate.h"
+#include "absl/base/macros.h"
+#include "absl/base/optimization.h"
+#include "absl/base/port.h"
+#include "absl/container/internal/compressed_tuple.h"
+#include "absl/memory/memory.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+
+constexpr static auto kFixedArrayUseDefault = static_cast<size_t>(-1);
+
+// -----------------------------------------------------------------------------
+// FixedArray
+// -----------------------------------------------------------------------------
+//
+// A `FixedArray` provides a run-time fixed-size array, allocating a small array
+// inline for efficiency.
+//
+// Most users should not specify an `inline_elements` argument and let
+// `FixedArray` automatically determine the number of elements
+// to store inline based on `sizeof(T)`. If `inline_elements` is specified, the
+// `FixedArray` implementation will use inline storage for arrays with a
+// length <= `inline_elements`.
+//
+// Note that a `FixedArray` constructed with a `size_type` argument will
+// default-initialize its values by leaving trivially constructible types
+// uninitialized (e.g. int, int[4], double), and others default-constructed.
+// This matches the behavior of c-style arrays and `std::array`, but not
+// `std::vector`.
+template <typename T, size_t N = kFixedArrayUseDefault,
+          typename A = std::allocator<T>>
+class FixedArray {
+  static_assert(!std::is_array<T>::value || std::extent<T>::value > 0,
+                "Arrays with unknown bounds cannot be used with FixedArray.");
+
+  static constexpr size_t kInlineBytesDefault = 256;
+
+  using AllocatorTraits = std::allocator_traits<A>;
+  // std::iterator_traits isn't guaranteed to be SFINAE-friendly until C++17,
+  // but this seems to be mostly pedantic.
+  template <typename Iterator>
+  using EnableIfForwardIterator = absl::enable_if_t<std::is_convertible<
+      typename std::iterator_traits<Iterator>::iterator_category,
+      std::forward_iterator_tag>::value>;
+  static constexpr bool NoexceptCopyable() {
+    return std::is_nothrow_copy_constructible<StorageElement>::value &&
+           absl::allocator_is_nothrow<allocator_type>::value;
+  }
+  static constexpr bool NoexceptMovable() {
+    return std::is_nothrow_move_constructible<StorageElement>::value &&
+           absl::allocator_is_nothrow<allocator_type>::value;
+  }
+  static constexpr bool DefaultConstructorIsNonTrivial() {
+    return !absl::is_trivially_default_constructible<StorageElement>::value;
+  }
+
+ public:
+  using allocator_type = typename AllocatorTraits::allocator_type;
+  using value_type = typename AllocatorTraits::value_type;
+  using pointer = typename AllocatorTraits::pointer;
+  using const_pointer = typename AllocatorTraits::const_pointer;
+  using reference = value_type&;
+  using const_reference = const value_type&;
+  using size_type = typename AllocatorTraits::size_type;
+  using difference_type = typename AllocatorTraits::difference_type;
+  using iterator = pointer;
+  using const_iterator = const_pointer;
+  using reverse_iterator = std::reverse_iterator<iterator>;
+  using const_reverse_iterator = std::reverse_iterator<const_iterator>;
+
+  static constexpr size_type inline_elements =
+      (N == kFixedArrayUseDefault ? kInlineBytesDefault / sizeof(value_type)
+                                  : static_cast<size_type>(N));
+
+  FixedArray(
+      const FixedArray& other,
+      const allocator_type& a = allocator_type()) noexcept(NoexceptCopyable())
+      : FixedArray(other.begin(), other.end(), a) {}
+
+  FixedArray(
+      FixedArray&& other,
+      const allocator_type& a = allocator_type()) noexcept(NoexceptMovable())
+      : FixedArray(std::make_move_iterator(other.begin()),
+                   std::make_move_iterator(other.end()), a) {}
+
+  // Creates an array object that can store `n` elements.
+  // Note that trivially constructible elements will be uninitialized.
+  explicit FixedArray(size_type n, const allocator_type& a = allocator_type())
+      : storage_(n, a) {
+    if (DefaultConstructorIsNonTrivial()) {
+      memory_internal::ConstructRange(storage_.alloc(), storage_.begin(),
+                                      storage_.end());
+    }
+  }
+
+  // Creates an array initialized with `n` copies of `val`.
+  FixedArray(size_type n, const value_type& val,
+             const allocator_type& a = allocator_type())
+      : storage_(n, a) {
+    memory_internal::ConstructRange(storage_.alloc(), storage_.begin(),
+                                    storage_.end(), val);
+  }
+
+  // Creates an array initialized with the size and contents of `init_list`.
+  FixedArray(std::initializer_list<value_type> init_list,
+             const allocator_type& a = allocator_type())
+      : FixedArray(init_list.begin(), init_list.end(), a) {}
+
+  // Creates an array initialized with the elements from the input
+  // range. The array's size will always be `std::distance(first, last)`.
+  // REQUIRES: Iterator must be a forward_iterator or better.
+  template <typename Iterator, EnableIfForwardIterator<Iterator>* = nullptr>
+  FixedArray(Iterator first, Iterator last,
+             const allocator_type& a = allocator_type())
+      : storage_(std::distance(first, last), a) {
+    memory_internal::CopyRange(storage_.alloc(), storage_.begin(), first, last);
+  }
+
+  ~FixedArray() noexcept {
+    for (auto* cur = storage_.begin(); cur != storage_.end(); ++cur) {
+      AllocatorTraits::destroy(storage_.alloc(), cur);
+    }
+  }
+
+  // Assignments are deleted because they break the invariant that the size of a
+  // `FixedArray` never changes.
+  void operator=(FixedArray&&) = delete;
+  void operator=(const FixedArray&) = delete;
+
+  // FixedArray::size()
+  //
+  // Returns the length of the fixed array.
+  size_type size() const { return storage_.size(); }
+
+  // FixedArray::max_size()
+  //
+  // Returns the largest possible value of `std::distance(begin(), end())` for a
+  // `FixedArray<T>`. This is equivalent to the most possible addressable bytes
+  // over the number of bytes taken by T.
+  constexpr size_type max_size() const {
+    return (std::numeric_limits<difference_type>::max)() / sizeof(value_type);
+  }
+
+  // FixedArray::empty()
+  //
+  // Returns whether or not the fixed array is empty.
+  bool empty() const { return size() == 0; }
+
+  // FixedArray::memsize()
+  //
+  // Returns the memory size of the fixed array in bytes.
+  size_t memsize() const { return size() * sizeof(value_type); }
+
+  // FixedArray::data()
+  //
+  // Returns a const T* pointer to elements of the `FixedArray`. This pointer
+  // can be used to access (but not modify) the contained elements.
+  const_pointer data() const { return AsValueType(storage_.begin()); }
+
+  // Overload of FixedArray::data() to return a T* pointer to elements of the
+  // fixed array. This pointer can be used to access and modify the contained
+  // elements.
+  pointer data() { return AsValueType(storage_.begin()); }
+
+  // FixedArray::operator[]
+  //
+  // Returns a reference the ith element of the fixed array.
+  // REQUIRES: 0 <= i < size()
+  reference operator[](size_type i) {
+    ABSL_HARDENING_ASSERT(i < size());
+    return data()[i];
+  }
+
+  // Overload of FixedArray::operator()[] to return a const reference to the
+  // ith element of the fixed array.
+  // REQUIRES: 0 <= i < size()
+  const_reference operator[](size_type i) const {
+    ABSL_HARDENING_ASSERT(i < size());
+    return data()[i];
+  }
+
+  // FixedArray::at
+  //
+  // Bounds-checked access.  Returns a reference to the ith element of the fixed
+  // array, or throws std::out_of_range
+  reference at(size_type i) {
+    if (ABSL_PREDICT_FALSE(i >= size())) {
+      base_internal::ThrowStdOutOfRange("FixedArray::at failed bounds check");
+    }
+    return data()[i];
+  }
+
+  // Overload of FixedArray::at() to return a const reference to the ith element
+  // of the fixed array.
+  const_reference at(size_type i) const {
+    if (ABSL_PREDICT_FALSE(i >= size())) {
+      base_internal::ThrowStdOutOfRange("FixedArray::at failed bounds check");
+    }
+    return data()[i];
+  }
+
+  // FixedArray::front()
+  //
+  // Returns a reference to the first element of the fixed array.
+  reference front() {
+    ABSL_HARDENING_ASSERT(!empty());
+    return data()[0];
+  }
+
+  // Overload of FixedArray::front() to return a reference to the first element
+  // of a fixed array of const values.
+  const_reference front() const {
+    ABSL_HARDENING_ASSERT(!empty());
+    return data()[0];
+  }
+
+  // FixedArray::back()
+  //
+  // Returns a reference to the last element of the fixed array.
+  reference back() {
+    ABSL_HARDENING_ASSERT(!empty());
+    return data()[size() - 1];
+  }
+
+  // Overload of FixedArray::back() to return a reference to the last element
+  // of a fixed array of const values.
+  const_reference back() const {
+    ABSL_HARDENING_ASSERT(!empty());
+    return data()[size() - 1];
+  }
+
+  // FixedArray::begin()
+  //
+  // Returns an iterator to the beginning of the fixed array.
+  iterator begin() { return data(); }
+
+  // Overload of FixedArray::begin() to return a const iterator to the
+  // beginning of the fixed array.
+  const_iterator begin() const { return data(); }
+
+  // FixedArray::cbegin()
+  //
+  // Returns a const iterator to the beginning of the fixed array.
+  const_iterator cbegin() const { return begin(); }
+
+  // FixedArray::end()
+  //
+  // Returns an iterator to the end of the fixed array.
+  iterator end() { return data() + size(); }
+
+  // Overload of FixedArray::end() to return a const iterator to the end of the
+  // fixed array.
+  const_iterator end() const { return data() + size(); }
+
+  // FixedArray::cend()
+  //
+  // Returns a const iterator to the end of the fixed array.
+  const_iterator cend() const { return end(); }
+
+  // FixedArray::rbegin()
+  //
+  // Returns a reverse iterator from the end of the fixed array.
+  reverse_iterator rbegin() { return reverse_iterator(end()); }
+
+  // Overload of FixedArray::rbegin() to return a const reverse iterator from
+  // the end of the fixed array.
+  const_reverse_iterator rbegin() const {
+    return const_reverse_iterator(end());
+  }
+
+  // FixedArray::crbegin()
+  //
+  // Returns a const reverse iterator from the end of the fixed array.
+  const_reverse_iterator crbegin() const { return rbegin(); }
+
+  // FixedArray::rend()
+  //
+  // Returns a reverse iterator from the beginning of the fixed array.
+  reverse_iterator rend() { return reverse_iterator(begin()); }
+
+  // Overload of FixedArray::rend() for returning a const reverse iterator
+  // from the beginning of the fixed array.
+  const_reverse_iterator rend() const {
+    return const_reverse_iterator(begin());
+  }
+
+  // FixedArray::crend()
+  //
+  // Returns a reverse iterator from the beginning of the fixed array.
+  const_reverse_iterator crend() const { return rend(); }
+
+  // FixedArray::fill()
+  //
+  // Assigns the given `value` to all elements in the fixed array.
+  void fill(const value_type& val) { std::fill(begin(), end(), val); }
+
+  // Relational operators. Equality operators are elementwise using
+  // `operator==`, while order operators order FixedArrays lexicographically.
+  friend bool operator==(const FixedArray& lhs, const FixedArray& rhs) {
+    return absl::equal(lhs.begin(), lhs.end(), rhs.begin(), rhs.end());
+  }
+
+  friend bool operator!=(const FixedArray& lhs, const FixedArray& rhs) {
+    return !(lhs == rhs);
+  }
+
+  friend bool operator<(const FixedArray& lhs, const FixedArray& rhs) {
+    return std::lexicographical_compare(lhs.begin(), lhs.end(), rhs.begin(),
+                                        rhs.end());
+  }
+
+  friend bool operator>(const FixedArray& lhs, const FixedArray& rhs) {
+    return rhs < lhs;
+  }
+
+  friend bool operator<=(const FixedArray& lhs, const FixedArray& rhs) {
+    return !(rhs < lhs);
+  }
+
+  friend bool operator>=(const FixedArray& lhs, const FixedArray& rhs) {
+    return !(lhs < rhs);
+  }
+
+  template <typename H>
+  friend H AbslHashValue(H h, const FixedArray& v) {
+    return H::combine(H::combine_contiguous(std::move(h), v.data(), v.size()),
+                      v.size());
+  }
+
+ private:
+  // StorageElement
+  //
+  // For FixedArrays with a C-style-array value_type, StorageElement is a POD
+  // wrapper struct called StorageElementWrapper that holds the value_type
+  // instance inside. This is needed for construction and destruction of the
+  // entire array regardless of how many dimensions it has. For all other cases,
+  // StorageElement is just an alias of value_type.
+  //
+  // Maintainer's Note: The simpler solution would be to simply wrap value_type
+  // in a struct whether it's an array or not. That causes some paranoid
+  // diagnostics to misfire, believing that 'data()' returns a pointer to a
+  // single element, rather than the packed array that it really is.
+  // e.g.:
+  //
+  //     FixedArray<char> buf(1);
+  //     sprintf(buf.data(), "foo");
+  //
+  //     error: call to int __builtin___sprintf_chk(etc...)
+  //     will always overflow destination buffer [-Werror]
+  //
+  template <typename OuterT, typename InnerT = absl::remove_extent_t<OuterT>,
+            size_t InnerN = std::extent<OuterT>::value>
+  struct StorageElementWrapper {
+    InnerT array[InnerN];
+  };
+
+  using StorageElement =
+      absl::conditional_t<std::is_array<value_type>::value,
+                          StorageElementWrapper<value_type>, value_type>;
+
+  static pointer AsValueType(pointer ptr) { return ptr; }
+  static pointer AsValueType(StorageElementWrapper<value_type>* ptr) {
+    return std::addressof(ptr->array);
+  }
+
+  static_assert(sizeof(StorageElement) == sizeof(value_type), "");
+  static_assert(alignof(StorageElement) == alignof(value_type), "");
+
+  class NonEmptyInlinedStorage {
+   public:
+    StorageElement* data() { return reinterpret_cast<StorageElement*>(buff_); }
+    void AnnotateConstruct(size_type n);
+    void AnnotateDestruct(size_type n);
+
+#ifdef ABSL_HAVE_ADDRESS_SANITIZER
+    void* RedzoneBegin() { return &redzone_begin_; }
+    void* RedzoneEnd() { return &redzone_end_ + 1; }
+#endif  // ABSL_HAVE_ADDRESS_SANITIZER
+
+   private:
+    ABSL_ADDRESS_SANITIZER_REDZONE(redzone_begin_);
+    alignas(StorageElement) char buff_[sizeof(StorageElement[inline_elements])];
+    ABSL_ADDRESS_SANITIZER_REDZONE(redzone_end_);
+  };
+
+  class EmptyInlinedStorage {
+   public:
+    StorageElement* data() { return nullptr; }
+    void AnnotateConstruct(size_type) {}
+    void AnnotateDestruct(size_type) {}
+  };
+
+  using InlinedStorage =
+      absl::conditional_t<inline_elements == 0, EmptyInlinedStorage,
+                          NonEmptyInlinedStorage>;
+
+  // Storage
+  //
+  // An instance of Storage manages the inline and out-of-line memory for
+  // instances of FixedArray. This guarantees that even when construction of
+  // individual elements fails in the FixedArray constructor body, the
+  // destructor for Storage will still be called and out-of-line memory will be
+  // properly deallocated.
+  //
+  class Storage : public InlinedStorage {
+   public:
+    Storage(size_type n, const allocator_type& a)
+        : size_alloc_(n, a), data_(InitializeData()) {}
+
+    ~Storage() noexcept {
+      if (UsingInlinedStorage(size())) {
+        InlinedStorage::AnnotateDestruct(size());
+      } else {
+        AllocatorTraits::deallocate(alloc(), AsValueType(begin()), size());
+      }
+    }
+
+    size_type size() const { return size_alloc_.template get<0>(); }
+    StorageElement* begin() const { return data_; }
+    StorageElement* end() const { return begin() + size(); }
+    allocator_type& alloc() { return size_alloc_.template get<1>(); }
+
+   private:
+    static bool UsingInlinedStorage(size_type n) {
+      return n <= inline_elements;
+    }
+
+    StorageElement* InitializeData() {
+      if (UsingInlinedStorage(size())) {
+        InlinedStorage::AnnotateConstruct(size());
+        return InlinedStorage::data();
+      } else {
+        return reinterpret_cast<StorageElement*>(
+            AllocatorTraits::allocate(alloc(), size()));
+      }
+    }
+
+    // `CompressedTuple` takes advantage of EBCO for stateless `allocator_type`s
+    container_internal::CompressedTuple<size_type, allocator_type> size_alloc_;
+    StorageElement* data_;
+  };
+
+  Storage storage_;
+};
+
+#ifdef ABSL_INTERNAL_NEED_REDUNDANT_CONSTEXPR_DECL
+template <typename T, size_t N, typename A>
+constexpr size_t FixedArray<T, N, A>::kInlineBytesDefault;
+
+template <typename T, size_t N, typename A>
+constexpr typename FixedArray<T, N, A>::size_type
+    FixedArray<T, N, A>::inline_elements;
+#endif
+
+template <typename T, size_t N, typename A>
+void FixedArray<T, N, A>::NonEmptyInlinedStorage::AnnotateConstruct(
+    typename FixedArray<T, N, A>::size_type n) {
+#ifdef ABSL_HAVE_ADDRESS_SANITIZER
+  if (!n) return;
+  ABSL_ANNOTATE_CONTIGUOUS_CONTAINER(data(), RedzoneEnd(), RedzoneEnd(),
+                                     data() + n);
+  ABSL_ANNOTATE_CONTIGUOUS_CONTAINER(RedzoneBegin(), data(), data(),
+                                     RedzoneBegin());
+#endif  // ABSL_HAVE_ADDRESS_SANITIZER
+  static_cast<void>(n);  // Mark used when not in asan mode
+}
+
+template <typename T, size_t N, typename A>
+void FixedArray<T, N, A>::NonEmptyInlinedStorage::AnnotateDestruct(
+    typename FixedArray<T, N, A>::size_type n) {
+#ifdef ABSL_HAVE_ADDRESS_SANITIZER
+  if (!n) return;
+  ABSL_ANNOTATE_CONTIGUOUS_CONTAINER(data(), RedzoneEnd(), data() + n,
+                                     RedzoneEnd());
+  ABSL_ANNOTATE_CONTIGUOUS_CONTAINER(RedzoneBegin(), data(), RedzoneBegin(),
+                                     data());
+#endif  // ABSL_HAVE_ADDRESS_SANITIZER
+  static_cast<void>(n);  // Mark used when not in asan mode
+}
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_CONTAINER_FIXED_ARRAY_H_
--- a/include/absl/container/flat_hash_map.h
+++ b/include/absl/container/flat_hash_map.h
@ -0,0 +1,613 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// -----------------------------------------------------------------------------
+// File: flat_hash_map.h
+// -----------------------------------------------------------------------------
+//
+// An `absl::flat_hash_map<K, V>` is an unordered associative container of
+// unique keys and associated values designed to be a more efficient replacement
+// for `std::unordered_map`. Like `unordered_map`, search, insertion, and
+// deletion of map elements can be done as an `O(1)` operation. However,
+// `flat_hash_map` (and other unordered associative containers known as the
+// collection of Abseil "Swiss tables") contain other optimizations that result
+// in both memory and computation advantages.
+//
+// In most cases, your default choice for a hash map should be a map of type
+// `flat_hash_map`.
+
+#ifndef ABSL_CONTAINER_FLAT_HASH_MAP_H_
+#define ABSL_CONTAINER_FLAT_HASH_MAP_H_
+
+#include <cstddef>
+#include <new>
+#include <type_traits>
+#include <utility>
+
+#include "absl/algorithm/container.h"
+#include "absl/base/macros.h"
+#include "absl/container/internal/container_memory.h"
+#include "absl/container/internal/hash_function_defaults.h"  // IWYU pragma: export
+#include "absl/container/internal/raw_hash_map.h"  // IWYU pragma: export
+#include "absl/memory/memory.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace container_internal {
+template <class K, class V>
+struct FlatHashMapPolicy;
+}  // namespace container_internal
+
+// -----------------------------------------------------------------------------
+// absl::flat_hash_map
+// -----------------------------------------------------------------------------
+//
+// An `absl::flat_hash_map<K, V>` is an unordered associative container which
+// has been optimized for both speed and memory footprint in most common use
+// cases. Its interface is similar to that of `std::unordered_map<K, V>` with
+// the following notable differences:
+//
+// * Requires keys that are CopyConstructible
+// * Requires values that are MoveConstructible
+// * Supports heterogeneous lookup, through `find()`, `operator[]()` and
+//   `insert()`, provided that the map is provided a compatible heterogeneous
+//   hashing function and equality operator.
+// * Invalidates any references and pointers to elements within the table after
+//   `rehash()`.
+// * Contains a `capacity()` member function indicating the number of element
+//   slots (open, deleted, and empty) within the hash map.
+// * Returns `void` from the `erase(iterator)` overload.
+//
+// By default, `flat_hash_map` uses the `absl::Hash` hashing framework.
+// All fundamental and Abseil types that support the `absl::Hash` framework have
+// a compatible equality operator for comparing insertions into `flat_hash_map`.
+// If your type is not yet supported by the `absl::Hash` framework, see
+// absl/hash/hash.h for information on extending Abseil hashing to user-defined
+// types.
+//
+// Using `absl::flat_hash_map` at interface boundaries in dynamically loaded
+// libraries (e.g. .dll, .so) is unsupported due to way `absl::Hash` values may
+// be randomized across dynamically loaded libraries.
+//
+// NOTE: A `flat_hash_map` stores its value types directly inside its
+// implementation array to avoid memory indirection. Because a `flat_hash_map`
+// is designed to move data when rehashed, map values will not retain pointer
+// stability. If you require pointer stability, or if your values are large,
+// consider using `absl::flat_hash_map<Key, std::unique_ptr<Value>>` instead.
+// If your types are not moveable or you require pointer stability for keys,
+// consider `absl::node_hash_map`.
+//
+// Example:
+//
+//   // Create a flat hash map of three strings (that map to strings)
+//   absl::flat_hash_map<std::string, std::string> ducks =
+//     {{"a", "huey"}, {"b", "dewey"}, {"c", "louie"}};
+//
+//  // Insert a new element into the flat hash map
+//  ducks.insert({"d", "donald"});
+//
+//  // Force a rehash of the flat hash map
+//  ducks.rehash(0);
+//
+//  // Find the element with the key "b"
+//  std::string search_key = "b";
+//  auto result = ducks.find(search_key);
+//  if (result != ducks.end()) {
+//    std::cout << "Result: " << result->second << std::endl;
+//  }
+template <class K, class V,
+          class Hash = absl::container_internal::hash_default_hash<K>,
+          class Eq = absl::container_internal::hash_default_eq<K>,
+          class Allocator = std::allocator<std::pair<const K, V>>>
+class flat_hash_map : public absl::container_internal::raw_hash_map<
+                          absl::container_internal::FlatHashMapPolicy<K, V>,
+                          Hash, Eq, Allocator> {
+  using Base = typename flat_hash_map::raw_hash_map;
+
+ public:
+  // Constructors and Assignment Operators
+  //
+  // A flat_hash_map supports the same overload set as `std::unordered_map`
+  // for construction and assignment:
+  //
+  // *  Default constructor
+  //
+  //    // No allocation for the table's elements is made.
+  //    absl::flat_hash_map<int, std::string> map1;
+  //
+  // * Initializer List constructor
+  //
+  //   absl::flat_hash_map<int, std::string> map2 =
+  //       {{1, "huey"}, {2, "dewey"}, {3, "louie"},};
+  //
+  // * Copy constructor
+  //
+  //   absl::flat_hash_map<int, std::string> map3(map2);
+  //
+  // * Copy assignment operator
+  //
+  //  // Hash functor and Comparator are copied as well
+  //  absl::flat_hash_map<int, std::string> map4;
+  //  map4 = map3;
+  //
+  // * Move constructor
+  //
+  //   // Move is guaranteed efficient
+  //   absl::flat_hash_map<int, std::string> map5(std::move(map4));
+  //
+  // * Move assignment operator
+  //
+  //   // May be efficient if allocators are compatible
+  //   absl::flat_hash_map<int, std::string> map6;
+  //   map6 = std::move(map5);
+  //
+  // * Range constructor
+  //
+  //   std::vector<std::pair<int, std::string>> v = {{1, "a"}, {2, "b"}};
+  //   absl::flat_hash_map<int, std::string> map7(v.begin(), v.end());
+  flat_hash_map() {}
+  using Base::Base;
+
+  // flat_hash_map::begin()
+  //
+  // Returns an iterator to the beginning of the `flat_hash_map`.
+  using Base::begin;
+
+  // flat_hash_map::cbegin()
+  //
+  // Returns a const iterator to the beginning of the `flat_hash_map`.
+  using Base::cbegin;
+
+  // flat_hash_map::cend()
+  //
+  // Returns a const iterator to the end of the `flat_hash_map`.
+  using Base::cend;
+
+  // flat_hash_map::end()
+  //
+  // Returns an iterator to the end of the `flat_hash_map`.
+  using Base::end;
+
+  // flat_hash_map::capacity()
+  //
+  // Returns the number of element slots (assigned, deleted, and empty)
+  // available within the `flat_hash_map`.
+  //
+  // NOTE: this member function is particular to `absl::flat_hash_map` and is
+  // not provided in the `std::unordered_map` API.
+  using Base::capacity;
+
+  // flat_hash_map::empty()
+  //
+  // Returns whether or not the `flat_hash_map` is empty.
+  using Base::empty;
+
+  // flat_hash_map::max_size()
+  //
+  // Returns the largest theoretical possible number of elements within a
+  // `flat_hash_map` under current memory constraints. This value can be thought
+  // of the largest value of `std::distance(begin(), end())` for a
+  // `flat_hash_map<K, V>`.
+  using Base::max_size;
+
+  // flat_hash_map::size()
+  //
+  // Returns the number of elements currently within the `flat_hash_map`.
+  using Base::size;
+
+  // flat_hash_map::clear()
+  //
+  // Removes all elements from the `flat_hash_map`. Invalidates any references,
+  // pointers, or iterators referring to contained elements.
+  //
+  // NOTE: this operation may shrink the underlying buffer. To avoid shrinking
+  // the underlying buffer call `erase(begin(), end())`.
+  using Base::clear;
+
+  // flat_hash_map::erase()
+  //
+  // Erases elements within the `flat_hash_map`. Erasing does not trigger a
+  // rehash. Overloads are listed below.
+  //
+  // void erase(const_iterator pos):
+  //
+  //   Erases the element at `position` of the `flat_hash_map`, returning
+  //   `void`.
+  //
+  //   NOTE: returning `void` in this case is different than that of STL
+  //   containers in general and `std::unordered_map` in particular (which
+  //   return an iterator to the element following the erased element). If that
+  //   iterator is needed, simply post increment the iterator:
+  //
+  //     map.erase(it++);
+  //
+  // iterator erase(const_iterator first, const_iterator last):
+  //
+  //   Erases the elements in the open interval [`first`, `last`), returning an
+  //   iterator pointing to `last`.
+  //
+  // size_type erase(const key_type& key):
+  //
+  //   Erases the element with the matching key, if it exists, returning the
+  //   number of elements erased (0 or 1).
+  using Base::erase;
+
+  // flat_hash_map::insert()
+  //
+  // Inserts an element of the specified value into the `flat_hash_map`,
+  // returning an iterator pointing to the newly inserted element, provided that
+  // an element with the given key does not already exist. If rehashing occurs
+  // due to the insertion, all iterators are invalidated. Overloads are listed
+  // below.
+  //
+  // std::pair<iterator,bool> insert(const init_type& value):
+  //
+  //   Inserts a value into the `flat_hash_map`. Returns a pair consisting of an
+  //   iterator to the inserted element (or to the element that prevented the
+  //   insertion) and a bool denoting whether the insertion took place.
+  //
+  // std::pair<iterator,bool> insert(T&& value):
+  // std::pair<iterator,bool> insert(init_type&& value):
+  //
+  //   Inserts a moveable value into the `flat_hash_map`. Returns a pair
+  //   consisting of an iterator to the inserted element (or to the element that
+  //   prevented the insertion) and a bool denoting whether the insertion took
+  //   place.
+  //
+  // iterator insert(const_iterator hint, const init_type& value):
+  // iterator insert(const_iterator hint, T&& value):
+  // iterator insert(const_iterator hint, init_type&& value);
+  //
+  //   Inserts a value, using the position of `hint` as a non-binding suggestion
+  //   for where to begin the insertion search. Returns an iterator to the
+  //   inserted element, or to the existing element that prevented the
+  //   insertion.
+  //
+  // void insert(InputIterator first, InputIterator last):
+  //
+  //   Inserts a range of values [`first`, `last`).
+  //
+  //   NOTE: Although the STL does not specify which element may be inserted if
+  //   multiple keys compare equivalently, for `flat_hash_map` we guarantee the
+  //   first match is inserted.
+  //
+  // void insert(std::initializer_list<init_type> ilist):
+  //
+  //   Inserts the elements within the initializer list `ilist`.
+  //
+  //   NOTE: Although the STL does not specify which element may be inserted if
+  //   multiple keys compare equivalently within the initializer list, for
+  //   `flat_hash_map` we guarantee the first match is inserted.
+  using Base::insert;
+
+  // flat_hash_map::insert_or_assign()
+  //
+  // Inserts an element of the specified value into the `flat_hash_map` provided
+  // that a value with the given key does not already exist, or replaces it with
+  // the element value if a key for that value already exists, returning an
+  // iterator pointing to the newly inserted element.  If rehashing occurs due
+  // to the insertion, all existing iterators are invalidated. Overloads are
+  // listed below.
+  //
+  // pair<iterator, bool> insert_or_assign(const init_type& k, T&& obj):
+  // pair<iterator, bool> insert_or_assign(init_type&& k, T&& obj):
+  //
+  //   Inserts/Assigns (or moves) the element of the specified key into the
+  //   `flat_hash_map`.
+  //
+  // iterator insert_or_assign(const_iterator hint,
+  //                           const init_type& k, T&& obj):
+  // iterator insert_or_assign(const_iterator hint, init_type&& k, T&& obj):
+  //
+  //   Inserts/Assigns (or moves) the element of the specified key into the
+  //   `flat_hash_map` using the position of `hint` as a non-binding suggestion
+  //   for where to begin the insertion search.
+  using Base::insert_or_assign;
+
+  // flat_hash_map::emplace()
+  //
+  // Inserts an element of the specified value by constructing it in-place
+  // within the `flat_hash_map`, provided that no element with the given key
+  // already exists.
+  //
+  // The element may be constructed even if there already is an element with the
+  // key in the container, in which case the newly constructed element will be
+  // destroyed immediately. Prefer `try_emplace()` unless your key is not
+  // copyable or moveable.
+  //
+  // If rehashing occurs due to the insertion, all iterators are invalidated.
+  using Base::emplace;
+
+  // flat_hash_map::emplace_hint()
+  //
+  // Inserts an element of the specified value by constructing it in-place
+  // within the `flat_hash_map`, using the position of `hint` as a non-binding
+  // suggestion for where to begin the insertion search, and only inserts
+  // provided that no element with the given key already exists.
+  //
+  // The element may be constructed even if there already is an element with the
+  // key in the container, in which case the newly constructed element will be
+  // destroyed immediately. Prefer `try_emplace()` unless your key is not
+  // copyable or moveable.
+  //
+  // If rehashing occurs due to the insertion, all iterators are invalidated.
+  using Base::emplace_hint;
+
+  // flat_hash_map::try_emplace()
+  //
+  // Inserts an element of the specified value by constructing it in-place
+  // within the `flat_hash_map`, provided that no element with the given key
+  // already exists. Unlike `emplace()`, if an element with the given key
+  // already exists, we guarantee that no element is constructed.
+  //
+  // If rehashing occurs due to the insertion, all iterators are invalidated.
+  // Overloads are listed below.
+  //
+  //   pair<iterator, bool> try_emplace(const key_type& k, Args&&... args):
+  //   pair<iterator, bool> try_emplace(key_type&& k, Args&&... args):
+  //
+  // Inserts (via copy or move) the element of the specified key into the
+  // `flat_hash_map`.
+  //
+  //   iterator try_emplace(const_iterator hint,
+  //                        const key_type& k, Args&&... args):
+  //   iterator try_emplace(const_iterator hint, key_type&& k, Args&&... args):
+  //
+  // Inserts (via copy or move) the element of the specified key into the
+  // `flat_hash_map` using the position of `hint` as a non-binding suggestion
+  // for where to begin the insertion search.
+  //
+  // All `try_emplace()` overloads make the same guarantees regarding rvalue
+  // arguments as `std::unordered_map::try_emplace()`, namely that these
+  // functions will not move from rvalue arguments if insertions do not happen.
+  using Base::try_emplace;
+
+  // flat_hash_map::extract()
+  //
+  // Extracts the indicated element, erasing it in the process, and returns it
+  // as a C++17-compatible node handle. Overloads are listed below.
+  //
+  // node_type extract(const_iterator position):
+  //
+  //   Extracts the key,value pair of the element at the indicated position and
+  //   returns a node handle owning that extracted data.
+  //
+  // node_type extract(const key_type& x):
+  //
+  //   Extracts the key,value pair of the element with a key matching the passed
+  //   key value and returns a node handle owning that extracted data. If the
+  //   `flat_hash_map` does not contain an element with a matching key, this
+  //   function returns an empty node handle.
+  //
+  // NOTE: when compiled in an earlier version of C++ than C++17,
+  // `node_type::key()` returns a const reference to the key instead of a
+  // mutable reference. We cannot safely return a mutable reference without
+  // std::launder (which is not available before C++17).
+  using Base::extract;
+
+  // flat_hash_map::merge()
+  //
+  // Extracts elements from a given `source` flat hash map into this
+  // `flat_hash_map`. If the destination `flat_hash_map` already contains an
+  // element with an equivalent key, that element is not extracted.
+  using Base::merge;
+
+  // flat_hash_map::swap(flat_hash_map& other)
+  //
+  // Exchanges the contents of this `flat_hash_map` with those of the `other`
+  // flat hash map, avoiding invocation of any move, copy, or swap operations on
+  // individual elements.
+  //
+  // All iterators and references on the `flat_hash_map` remain valid, excepting
+  // for the past-the-end iterator, which is invalidated.
+  //
+  // `swap()` requires that the flat hash map's hashing and key equivalence
+  // functions be Swappable, and are exchanged using unqualified calls to
+  // non-member `swap()`. If the map's allocator has
+  // `std::allocator_traits<allocator_type>::propagate_on_container_swap::value`
+  // set to `true`, the allocators are also exchanged using an unqualified call
+  // to non-member `swap()`; otherwise, the allocators are not swapped.
+  using Base::swap;
+
+  // flat_hash_map::rehash(count)
+  //
+  // Rehashes the `flat_hash_map`, setting the number of slots to be at least
+  // the passed value. If the new number of slots increases the load factor more
+  // than the current maximum load factor
+  // (`count` < `size()` / `max_load_factor()`), then the new number of slots
+  // will be at least `size()` / `max_load_factor()`.
+  //
+  // To force a rehash, pass rehash(0).
+  //
+  // NOTE: unlike behavior in `std::unordered_map`, references are also
+  // invalidated upon a `rehash()`.
+  using Base::rehash;
+
+  // flat_hash_map::reserve(count)
+  //
+  // Sets the number of slots in the `flat_hash_map` to the number needed to
+  // accommodate at least `count` total elements without exceeding the current
+  // maximum load factor, and may rehash the container if needed.
+  using Base::reserve;
+
+  // flat_hash_map::at()
+  //
+  // Returns a reference to the mapped value of the element with key equivalent
+  // to the passed key.
+  using Base::at;
+
+  // flat_hash_map::contains()
+  //
+  // Determines whether an element with a key comparing equal to the given `key`
+  // exists within the `flat_hash_map`, returning `true` if so or `false`
+  // otherwise.
+  using Base::contains;
+
+  // flat_hash_map::count(const Key& key) const
+  //
+  // Returns the number of elements with a key comparing equal to the given
+  // `key` within the `flat_hash_map`. note that this function will return
+  // either `1` or `0` since duplicate keys are not allowed within a
+  // `flat_hash_map`.
+  using Base::count;
+
+  // flat_hash_map::equal_range()
+  //
+  // Returns a closed range [first, last], defined by a `std::pair` of two
+  // iterators, containing all elements with the passed key in the
+  // `flat_hash_map`.
+  using Base::equal_range;
+
+  // flat_hash_map::find()
+  //
+  // Finds an element with the passed `key` within the `flat_hash_map`.
+  using Base::find;
+
+  // flat_hash_map::operator[]()
+  //
+  // Returns a reference to the value mapped to the passed key within the
+  // `flat_hash_map`, performing an `insert()` if the key does not already
+  // exist.
+  //
+  // If an insertion occurs and results in a rehashing of the container, all
+  // iterators are invalidated. Otherwise iterators are not affected and
+  // references are not invalidated. Overloads are listed below.
+  //
+  // T& operator[](const Key& key):
+  //
+  //   Inserts an init_type object constructed in-place if the element with the
+  //   given key does not exist.
+  //
+  // T& operator[](Key&& key):
+  //
+  //   Inserts an init_type object constructed in-place provided that an element
+  //   with the given key does not exist.
+  using Base::operator[];
+
+  // flat_hash_map::bucket_count()
+  //
+  // Returns the number of "buckets" within the `flat_hash_map`. Note that
+  // because a flat hash map contains all elements within its internal storage,
+  // this value simply equals the current capacity of the `flat_hash_map`.
+  using Base::bucket_count;
+
+  // flat_hash_map::load_factor()
+  //
+  // Returns the current load factor of the `flat_hash_map` (the average number
+  // of slots occupied with a value within the hash map).
+  using Base::load_factor;
+
+  // flat_hash_map::max_load_factor()
+  //
+  // Manages the maximum load factor of the `flat_hash_map`. Overloads are
+  // listed below.
+  //
+  // float flat_hash_map::max_load_factor()
+  //
+  //   Returns the current maximum load factor of the `flat_hash_map`.
+  //
+  // void flat_hash_map::max_load_factor(float ml)
+  //
+  //   Sets the maximum load factor of the `flat_hash_map` to the passed value.
+  //
+  //   NOTE: This overload is provided only for API compatibility with the STL;
+  //   `flat_hash_map` will ignore any set load factor and manage its rehashing
+  //   internally as an implementation detail.
+  using Base::max_load_factor;
+
+  // flat_hash_map::get_allocator()
+  //
+  // Returns the allocator function associated with this `flat_hash_map`.
+  using Base::get_allocator;
+
+  // flat_hash_map::hash_function()
+  //
+  // Returns the hashing function used to hash the keys within this
+  // `flat_hash_map`.
+  using Base::hash_function;
+
+  // flat_hash_map::key_eq()
+  //
+  // Returns the function used for comparing keys equality.
+  using Base::key_eq;
+};
+
+// erase_if(flat_hash_map<>, Pred)
+//
+// Erases all elements that satisfy the predicate `pred` from the container `c`.
+// Returns the number of erased elements.
+template <typename K, typename V, typename H, typename E, typename A,
+          typename Predicate>
+typename flat_hash_map<K, V, H, E, A>::size_type erase_if(
+    flat_hash_map<K, V, H, E, A>& c, Predicate pred) {
+  return container_internal::EraseIf(pred, &c);
+}
+
+namespace container_internal {
+
+template <class K, class V>
+struct FlatHashMapPolicy {
+  using slot_policy = container_internal::map_slot_policy<K, V>;
+  using slot_type = typename slot_policy::slot_type;
+  using key_type = K;
+  using mapped_type = V;
+  using init_type = std::pair</*non const*/ key_type, mapped_type>;
+
+  template <class Allocator, class... Args>
+  static void construct(Allocator* alloc, slot_type* slot, Args&&... args) {
+    slot_policy::construct(alloc, slot, std::forward<Args>(args)...);
+  }
+
+  template <class Allocator>
+  static void destroy(Allocator* alloc, slot_type* slot) {
+    slot_policy::destroy(alloc, slot);
+  }
+
+  template <class Allocator>
+  static void transfer(Allocator* alloc, slot_type* new_slot,
+                       slot_type* old_slot) {
+    slot_policy::transfer(alloc, new_slot, old_slot);
+  }
+
+  template <class F, class... Args>
+  static decltype(absl::container_internal::DecomposePair(
+      std::declval<F>(), std::declval<Args>()...))
+  apply(F&& f, Args&&... args) {
+    return absl::container_internal::DecomposePair(std::forward<F>(f),
+                                                   std::forward<Args>(args)...);
+  }
+
+  static size_t space_used(const slot_type*) { return 0; }
+
+  static std::pair<const K, V>& element(slot_type* slot) { return slot->value; }
+
+  static V& value(std::pair<const K, V>* kv) { return kv->second; }
+  static const V& value(const std::pair<const K, V>* kv) { return kv->second; }
+};
+
+}  // namespace container_internal
+
+namespace container_algorithm_internal {
+
+// Specialization of trait in absl/algorithm/container.h
+template <class Key, class T, class Hash, class KeyEqual, class Allocator>
+struct IsUnorderedContainer<
+    absl::flat_hash_map<Key, T, Hash, KeyEqual, Allocator>> : std::true_type {};
+
+}  // namespace container_algorithm_internal
+
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_CONTAINER_FLAT_HASH_MAP_H_
--- a/include/absl/container/flat_hash_set.h
+++ b/include/absl/container/flat_hash_set.h
@ -0,0 +1,510 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// -----------------------------------------------------------------------------
+// File: flat_hash_set.h
+// -----------------------------------------------------------------------------
+//
+// An `absl::flat_hash_set<T>` is an unordered associative container designed to
+// be a more efficient replacement for `std::unordered_set`. Like
+// `unordered_set`, search, insertion, and deletion of set elements can be done
+// as an `O(1)` operation. However, `flat_hash_set` (and other unordered
+// associative containers known as the collection of Abseil "Swiss tables")
+// contain other optimizations that result in both memory and computation
+// advantages.
+//
+// In most cases, your default choice for a hash set should be a set of type
+// `flat_hash_set`.
+#ifndef ABSL_CONTAINER_FLAT_HASH_SET_H_
+#define ABSL_CONTAINER_FLAT_HASH_SET_H_
+
+#include <type_traits>
+#include <utility>
+
+#include "absl/algorithm/container.h"
+#include "absl/base/macros.h"
+#include "absl/container/internal/container_memory.h"
+#include "absl/container/internal/hash_function_defaults.h"  // IWYU pragma: export
+#include "absl/container/internal/raw_hash_set.h"  // IWYU pragma: export
+#include "absl/memory/memory.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace container_internal {
+template <typename T>
+struct FlatHashSetPolicy;
+}  // namespace container_internal
+
+// -----------------------------------------------------------------------------
+// absl::flat_hash_set
+// -----------------------------------------------------------------------------
+//
+// An `absl::flat_hash_set<T>` is an unordered associative container which has
+// been optimized for both speed and memory footprint in most common use cases.
+// Its interface is similar to that of `std::unordered_set<T>` with the
+// following notable differences:
+//
+// * Requires keys that are CopyConstructible
+// * Supports heterogeneous lookup, through `find()` and `insert()`, provided
+//   that the set is provided a compatible heterogeneous hashing function and
+//   equality operator.
+// * Invalidates any references and pointers to elements within the table after
+//   `rehash()`.
+// * Contains a `capacity()` member function indicating the number of element
+//   slots (open, deleted, and empty) within the hash set.
+// * Returns `void` from the `erase(iterator)` overload.
+//
+// By default, `flat_hash_set` uses the `absl::Hash` hashing framework. All
+// fundamental and Abseil types that support the `absl::Hash` framework have a
+// compatible equality operator for comparing insertions into `flat_hash_set`.
+// If your type is not yet supported by the `absl::Hash` framework, see
+// absl/hash/hash.h for information on extending Abseil hashing to user-defined
+// types.
+//
+// Using `absl::flat_hash_set` at interface boundaries in dynamically loaded
+// libraries (e.g. .dll, .so) is unsupported due to way `absl::Hash` values may
+// be randomized across dynamically loaded libraries.
+//
+// NOTE: A `flat_hash_set` stores its keys directly inside its implementation
+// array to avoid memory indirection. Because a `flat_hash_set` is designed to
+// move data when rehashed, set keys will not retain pointer stability. If you
+// require pointer stability, consider using
+// `absl::flat_hash_set<std::unique_ptr<T>>`. If your type is not moveable and
+// you require pointer stability, consider `absl::node_hash_set` instead.
+//
+// Example:
+//
+//   // Create a flat hash set of three strings
+//   absl::flat_hash_set<std::string> ducks =
+//     {"huey", "dewey", "louie"};
+//
+//  // Insert a new element into the flat hash set
+//  ducks.insert("donald");
+//
+//  // Force a rehash of the flat hash set
+//  ducks.rehash(0);
+//
+//  // See if "dewey" is present
+//  if (ducks.contains("dewey")) {
+//    std::cout << "We found dewey!" << std::endl;
+//  }
+template <class T, class Hash = absl::container_internal::hash_default_hash<T>,
+          class Eq = absl::container_internal::hash_default_eq<T>,
+          class Allocator = std::allocator<T>>
+class flat_hash_set
+    : public absl::container_internal::raw_hash_set<
+          absl::container_internal::FlatHashSetPolicy<T>, Hash, Eq, Allocator> {
+  using Base = typename flat_hash_set::raw_hash_set;
+
+ public:
+  // Constructors and Assignment Operators
+  //
+  // A flat_hash_set supports the same overload set as `std::unordered_set`
+  // for construction and assignment:
+  //
+  // *  Default constructor
+  //
+  //    // No allocation for the table's elements is made.
+  //    absl::flat_hash_set<std::string> set1;
+  //
+  // * Initializer List constructor
+  //
+  //   absl::flat_hash_set<std::string> set2 =
+  //       {{"huey"}, {"dewey"}, {"louie"},};
+  //
+  // * Copy constructor
+  //
+  //   absl::flat_hash_set<std::string> set3(set2);
+  //
+  // * Copy assignment operator
+  //
+  //  // Hash functor and Comparator are copied as well
+  //  absl::flat_hash_set<std::string> set4;
+  //  set4 = set3;
+  //
+  // * Move constructor
+  //
+  //   // Move is guaranteed efficient
+  //   absl::flat_hash_set<std::string> set5(std::move(set4));
+  //
+  // * Move assignment operator
+  //
+  //   // May be efficient if allocators are compatible
+  //   absl::flat_hash_set<std::string> set6;
+  //   set6 = std::move(set5);
+  //
+  // * Range constructor
+  //
+  //   std::vector<std::string> v = {"a", "b"};
+  //   absl::flat_hash_set<std::string> set7(v.begin(), v.end());
+  flat_hash_set() {}
+  using Base::Base;
+
+  // flat_hash_set::begin()
+  //
+  // Returns an iterator to the beginning of the `flat_hash_set`.
+  using Base::begin;
+
+  // flat_hash_set::cbegin()
+  //
+  // Returns a const iterator to the beginning of the `flat_hash_set`.
+  using Base::cbegin;
+
+  // flat_hash_set::cend()
+  //
+  // Returns a const iterator to the end of the `flat_hash_set`.
+  using Base::cend;
+
+  // flat_hash_set::end()
+  //
+  // Returns an iterator to the end of the `flat_hash_set`.
+  using Base::end;
+
+  // flat_hash_set::capacity()
+  //
+  // Returns the number of element slots (assigned, deleted, and empty)
+  // available within the `flat_hash_set`.
+  //
+  // NOTE: this member function is particular to `absl::flat_hash_set` and is
+  // not provided in the `std::unordered_set` API.
+  using Base::capacity;
+
+  // flat_hash_set::empty()
+  //
+  // Returns whether or not the `flat_hash_set` is empty.
+  using Base::empty;
+
+  // flat_hash_set::max_size()
+  //
+  // Returns the largest theoretical possible number of elements within a
+  // `flat_hash_set` under current memory constraints. This value can be thought
+  // of the largest value of `std::distance(begin(), end())` for a
+  // `flat_hash_set<T>`.
+  using Base::max_size;
+
+  // flat_hash_set::size()
+  //
+  // Returns the number of elements currently within the `flat_hash_set`.
+  using Base::size;
+
+  // flat_hash_set::clear()
+  //
+  // Removes all elements from the `flat_hash_set`. Invalidates any references,
+  // pointers, or iterators referring to contained elements.
+  //
+  // NOTE: this operation may shrink the underlying buffer. To avoid shrinking
+  // the underlying buffer call `erase(begin(), end())`.
+  using Base::clear;
+
+  // flat_hash_set::erase()
+  //
+  // Erases elements within the `flat_hash_set`. Erasing does not trigger a
+  // rehash. Overloads are listed below.
+  //
+  // void erase(const_iterator pos):
+  //
+  //   Erases the element at `position` of the `flat_hash_set`, returning
+  //   `void`.
+  //
+  //   NOTE: returning `void` in this case is different than that of STL
+  //   containers in general and `std::unordered_set` in particular (which
+  //   return an iterator to the element following the erased element). If that
+  //   iterator is needed, simply post increment the iterator:
+  //
+  //     set.erase(it++);
+  //
+  // iterator erase(const_iterator first, const_iterator last):
+  //
+  //   Erases the elements in the open interval [`first`, `last`), returning an
+  //   iterator pointing to `last`.
+  //
+  // size_type erase(const key_type& key):
+  //
+  //   Erases the element with the matching key, if it exists, returning the
+  //   number of elements erased (0 or 1).
+  using Base::erase;
+
+  // flat_hash_set::insert()
+  //
+  // Inserts an element of the specified value into the `flat_hash_set`,
+  // returning an iterator pointing to the newly inserted element, provided that
+  // an element with the given key does not already exist. If rehashing occurs
+  // due to the insertion, all iterators are invalidated. Overloads are listed
+  // below.
+  //
+  // std::pair<iterator,bool> insert(const T& value):
+  //
+  //   Inserts a value into the `flat_hash_set`. Returns a pair consisting of an
+  //   iterator to the inserted element (or to the element that prevented the
+  //   insertion) and a bool denoting whether the insertion took place.
+  //
+  // std::pair<iterator,bool> insert(T&& value):
+  //
+  //   Inserts a moveable value into the `flat_hash_set`. Returns a pair
+  //   consisting of an iterator to the inserted element (or to the element that
+  //   prevented the insertion) and a bool denoting whether the insertion took
+  //   place.
+  //
+  // iterator insert(const_iterator hint, const T& value):
+  // iterator insert(const_iterator hint, T&& value):
+  //
+  //   Inserts a value, using the position of `hint` as a non-binding suggestion
+  //   for where to begin the insertion search. Returns an iterator to the
+  //   inserted element, or to the existing element that prevented the
+  //   insertion.
+  //
+  // void insert(InputIterator first, InputIterator last):
+  //
+  //   Inserts a range of values [`first`, `last`).
+  //
+  //   NOTE: Although the STL does not specify which element may be inserted if
+  //   multiple keys compare equivalently, for `flat_hash_set` we guarantee the
+  //   first match is inserted.
+  //
+  // void insert(std::initializer_list<T> ilist):
+  //
+  //   Inserts the elements within the initializer list `ilist`.
+  //
+  //   NOTE: Although the STL does not specify which element may be inserted if
+  //   multiple keys compare equivalently within the initializer list, for
+  //   `flat_hash_set` we guarantee the first match is inserted.
+  using Base::insert;
+
+  // flat_hash_set::emplace()
+  //
+  // Inserts an element of the specified value by constructing it in-place
+  // within the `flat_hash_set`, provided that no element with the given key
+  // already exists.
+  //
+  // The element may be constructed even if there already is an element with the
+  // key in the container, in which case the newly constructed element will be
+  // destroyed immediately.
+  //
+  // If rehashing occurs due to the insertion, all iterators are invalidated.
+  using Base::emplace;
+
+  // flat_hash_set::emplace_hint()
+  //
+  // Inserts an element of the specified value by constructing it in-place
+  // within the `flat_hash_set`, using the position of `hint` as a non-binding
+  // suggestion for where to begin the insertion search, and only inserts
+  // provided that no element with the given key already exists.
+  //
+  // The element may be constructed even if there already is an element with the
+  // key in the container, in which case the newly constructed element will be
+  // destroyed immediately.
+  //
+  // If rehashing occurs due to the insertion, all iterators are invalidated.
+  using Base::emplace_hint;
+
+  // flat_hash_set::extract()
+  //
+  // Extracts the indicated element, erasing it in the process, and returns it
+  // as a C++17-compatible node handle. Overloads are listed below.
+  //
+  // node_type extract(const_iterator position):
+  //
+  //   Extracts the element at the indicated position and returns a node handle
+  //   owning that extracted data.
+  //
+  // node_type extract(const key_type& x):
+  //
+  //   Extracts the element with the key matching the passed key value and
+  //   returns a node handle owning that extracted data. If the `flat_hash_set`
+  //   does not contain an element with a matching key, this function returns an
+  //   empty node handle.
+  using Base::extract;
+
+  // flat_hash_set::merge()
+  //
+  // Extracts elements from a given `source` flat hash set into this
+  // `flat_hash_set`. If the destination `flat_hash_set` already contains an
+  // element with an equivalent key, that element is not extracted.
+  using Base::merge;
+
+  // flat_hash_set::swap(flat_hash_set& other)
+  //
+  // Exchanges the contents of this `flat_hash_set` with those of the `other`
+  // flat hash set, avoiding invocation of any move, copy, or swap operations on
+  // individual elements.
+  //
+  // All iterators and references on the `flat_hash_set` remain valid, excepting
+  // for the past-the-end iterator, which is invalidated.
+  //
+  // `swap()` requires that the flat hash set's hashing and key equivalence
+  // functions be Swappable, and are exchaged using unqualified calls to
+  // non-member `swap()`. If the set's allocator has
+  // `std::allocator_traits<allocator_type>::propagate_on_container_swap::value`
+  // set to `true`, the allocators are also exchanged using an unqualified call
+  // to non-member `swap()`; otherwise, the allocators are not swapped.
+  using Base::swap;
+
+  // flat_hash_set::rehash(count)
+  //
+  // Rehashes the `flat_hash_set`, setting the number of slots to be at least
+  // the passed value. If the new number of slots increases the load factor more
+  // than the current maximum load factor
+  // (`count` < `size()` / `max_load_factor()`), then the new number of slots
+  // will be at least `size()` / `max_load_factor()`.
+  //
+  // To force a rehash, pass rehash(0).
+  //
+  // NOTE: unlike behavior in `std::unordered_set`, references are also
+  // invalidated upon a `rehash()`.
+  using Base::rehash;
+
+  // flat_hash_set::reserve(count)
+  //
+  // Sets the number of slots in the `flat_hash_set` to the number needed to
+  // accommodate at least `count` total elements without exceeding the current
+  // maximum load factor, and may rehash the container if needed.
+  using Base::reserve;
+
+  // flat_hash_set::contains()
+  //
+  // Determines whether an element comparing equal to the given `key` exists
+  // within the `flat_hash_set`, returning `true` if so or `false` otherwise.
+  using Base::contains;
+
+  // flat_hash_set::count(const Key& key) const
+  //
+  // Returns the number of elements comparing equal to the given `key` within
+  // the `flat_hash_set`. note that this function will return either `1` or `0`
+  // since duplicate elements are not allowed within a `flat_hash_set`.
+  using Base::count;
+
+  // flat_hash_set::equal_range()
+  //
+  // Returns a closed range [first, last], defined by a `std::pair` of two
+  // iterators, containing all elements with the passed key in the
+  // `flat_hash_set`.
+  using Base::equal_range;
+
+  // flat_hash_set::find()
+  //
+  // Finds an element with the passed `key` within the `flat_hash_set`.
+  using Base::find;
+
+  // flat_hash_set::bucket_count()
+  //
+  // Returns the number of "buckets" within the `flat_hash_set`. Note that
+  // because a flat hash set contains all elements within its internal storage,
+  // this value simply equals the current capacity of the `flat_hash_set`.
+  using Base::bucket_count;
+
+  // flat_hash_set::load_factor()
+  //
+  // Returns the current load factor of the `flat_hash_set` (the average number
+  // of slots occupied with a value within the hash set).
+  using Base::load_factor;
+
+  // flat_hash_set::max_load_factor()
+  //
+  // Manages the maximum load factor of the `flat_hash_set`. Overloads are
+  // listed below.
+  //
+  // float flat_hash_set::max_load_factor()
+  //
+  //   Returns the current maximum load factor of the `flat_hash_set`.
+  //
+  // void flat_hash_set::max_load_factor(float ml)
+  //
+  //   Sets the maximum load factor of the `flat_hash_set` to the passed value.
+  //
+  //   NOTE: This overload is provided only for API compatibility with the STL;
+  //   `flat_hash_set` will ignore any set load factor and manage its rehashing
+  //   internally as an implementation detail.
+  using Base::max_load_factor;
+
+  // flat_hash_set::get_allocator()
+  //
+  // Returns the allocator function associated with this `flat_hash_set`.
+  using Base::get_allocator;
+
+  // flat_hash_set::hash_function()
+  //
+  // Returns the hashing function used to hash the keys within this
+  // `flat_hash_set`.
+  using Base::hash_function;
+
+  // flat_hash_set::key_eq()
+  //
+  // Returns the function used for comparing keys equality.
+  using Base::key_eq;
+};
+
+// erase_if(flat_hash_set<>, Pred)
+//
+// Erases all elements that satisfy the predicate `pred` from the container `c`.
+// Returns the number of erased elements.
+template <typename T, typename H, typename E, typename A, typename Predicate>
+typename flat_hash_set<T, H, E, A>::size_type erase_if(
+    flat_hash_set<T, H, E, A>& c, Predicate pred) {
+  return container_internal::EraseIf(pred, &c);
+}
+
+namespace container_internal {
+
+template <class T>
+struct FlatHashSetPolicy {
+  using slot_type = T;
+  using key_type = T;
+  using init_type = T;
+  using constant_iterators = std::true_type;
+
+  template <class Allocator, class... Args>
+  static void construct(Allocator* alloc, slot_type* slot, Args&&... args) {
+    absl::allocator_traits<Allocator>::construct(*alloc, slot,
+                                                 std::forward<Args>(args)...);
+  }
+
+  template <class Allocator>
+  static void destroy(Allocator* alloc, slot_type* slot) {
+    absl::allocator_traits<Allocator>::destroy(*alloc, slot);
+  }
+
+  template <class Allocator>
+  static void transfer(Allocator* alloc, slot_type* new_slot,
+                       slot_type* old_slot) {
+    construct(alloc, new_slot, std::move(*old_slot));
+    destroy(alloc, old_slot);
+  }
+
+  static T& element(slot_type* slot) { return *slot; }
+
+  template <class F, class... Args>
+  static decltype(absl::container_internal::DecomposeValue(
+      std::declval<F>(), std::declval<Args>()...))
+  apply(F&& f, Args&&... args) {
+    return absl::container_internal::DecomposeValue(
+        std::forward<F>(f), std::forward<Args>(args)...);
+  }
+
+  static size_t space_used(const T*) { return 0; }
+};
+}  // namespace container_internal
+
+namespace container_algorithm_internal {
+
+// Specialization of trait in absl/algorithm/container.h
+template <class Key, class Hash, class KeyEqual, class Allocator>
+struct IsUnorderedContainer<absl::flat_hash_set<Key, Hash, KeyEqual, Allocator>>
+    : std::true_type {};
+
+}  // namespace container_algorithm_internal
+
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_CONTAINER_FLAT_HASH_SET_H_
--- a/include/absl/container/inlined_vector.h
+++ b/include/absl/container/inlined_vector.h
@ -0,0 +1,866 @@
+// Copyright 2019 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// -----------------------------------------------------------------------------
+// File: inlined_vector.h
+// -----------------------------------------------------------------------------
+//
+// This header file contains the declaration and definition of an "inlined
+// vector" which behaves in an equivalent fashion to a `std::vector`, except
+// that storage for small sequences of the vector are provided inline without
+// requiring any heap allocation.
+//
+// An `absl::InlinedVector<T, N>` specifies the default capacity `N` as one of
+// its template parameters. Instances where `size() <= N` hold contained
+// elements in inline space. Typically `N` is very small so that sequences that
+// are expected to be short do not require allocations.
+//
+// An `absl::InlinedVector` does not usually require a specific allocator. If
+// the inlined vector grows beyond its initial constraints, it will need to
+// allocate (as any normal `std::vector` would). This is usually performed with
+// the default allocator (defined as `std::allocator<T>`). Optionally, a custom
+// allocator type may be specified as `A` in `absl::InlinedVector<T, N, A>`.
+
+#ifndef ABSL_CONTAINER_INLINED_VECTOR_H_
+#define ABSL_CONTAINER_INLINED_VECTOR_H_
+
+#include <algorithm>
+#include <cstddef>
+#include <cstdlib>
+#include <cstring>
+#include <initializer_list>
+#include <iterator>
+#include <memory>
+#include <type_traits>
+#include <utility>
+
+#include "absl/algorithm/algorithm.h"
+#include "absl/base/internal/throw_delegate.h"
+#include "absl/base/macros.h"
+#include "absl/base/optimization.h"
+#include "absl/base/port.h"
+#include "absl/container/internal/inlined_vector.h"
+#include "absl/memory/memory.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+// -----------------------------------------------------------------------------
+// InlinedVector
+// -----------------------------------------------------------------------------
+//
+// An `absl::InlinedVector` is designed to be a drop-in replacement for
+// `std::vector` for use cases where the vector's size is sufficiently small
+// that it can be inlined. If the inlined vector does grow beyond its estimated
+// capacity, it will trigger an initial allocation on the heap, and will behave
+// as a `std::vector`. The API of the `absl::InlinedVector` within this file is
+// designed to cover the same API footprint as covered by `std::vector`.
+template <typename T, size_t N, typename A = std::allocator<T>>
+class InlinedVector {
+  static_assert(N > 0, "`absl::InlinedVector` requires an inlined capacity.");
+
+  using Storage = inlined_vector_internal::Storage<T, N, A>;
+
+  template <typename TheA>
+  using AllocatorTraits = inlined_vector_internal::AllocatorTraits<TheA>;
+  template <typename TheA>
+  using MoveIterator = inlined_vector_internal::MoveIterator<TheA>;
+  template <typename TheA>
+  using IsMemcpyOk = inlined_vector_internal::IsMemcpyOk<TheA>;
+
+  template <typename TheA, typename Iterator>
+  using IteratorValueAdapter =
+      inlined_vector_internal::IteratorValueAdapter<TheA, Iterator>;
+  template <typename TheA>
+  using CopyValueAdapter = inlined_vector_internal::CopyValueAdapter<TheA>;
+  template <typename TheA>
+  using DefaultValueAdapter =
+      inlined_vector_internal::DefaultValueAdapter<TheA>;
+
+  template <typename Iterator>
+  using EnableIfAtLeastForwardIterator = absl::enable_if_t<
+      inlined_vector_internal::IsAtLeastForwardIterator<Iterator>::value, int>;
+  template <typename Iterator>
+  using DisableIfAtLeastForwardIterator = absl::enable_if_t<
+      !inlined_vector_internal::IsAtLeastForwardIterator<Iterator>::value, int>;
+
+ public:
+  using allocator_type = A;
+  using value_type = inlined_vector_internal::ValueType<A>;
+  using pointer = inlined_vector_internal::Pointer<A>;
+  using const_pointer = inlined_vector_internal::ConstPointer<A>;
+  using size_type = inlined_vector_internal::SizeType<A>;
+  using difference_type = inlined_vector_internal::DifferenceType<A>;
+  using reference = inlined_vector_internal::Reference<A>;
+  using const_reference = inlined_vector_internal::ConstReference<A>;
+  using iterator = inlined_vector_internal::Iterator<A>;
+  using const_iterator = inlined_vector_internal::ConstIterator<A>;
+  using reverse_iterator = inlined_vector_internal::ReverseIterator<A>;
+  using const_reverse_iterator =
+      inlined_vector_internal::ConstReverseIterator<A>;
+
+  // ---------------------------------------------------------------------------
+  // InlinedVector Constructors and Destructor
+  // ---------------------------------------------------------------------------
+
+  // Creates an empty inlined vector with a value-initialized allocator.
+  InlinedVector() noexcept(noexcept(allocator_type())) : storage_() {}
+
+  // Creates an empty inlined vector with a copy of `allocator`.
+  explicit InlinedVector(const allocator_type& allocator) noexcept
+      : storage_(allocator) {}
+
+  // Creates an inlined vector with `n` copies of `value_type()`.
+  explicit InlinedVector(size_type n,
+                         const allocator_type& allocator = allocator_type())
+      : storage_(allocator) {
+    storage_.Initialize(DefaultValueAdapter<A>(), n);
+  }
+
+  // Creates an inlined vector with `n` copies of `v`.
+  InlinedVector(size_type n, const_reference v,
+                const allocator_type& allocator = allocator_type())
+      : storage_(allocator) {
+    storage_.Initialize(CopyValueAdapter<A>(std::addressof(v)), n);
+  }
+
+  // Creates an inlined vector with copies of the elements of `list`.
+  InlinedVector(std::initializer_list<value_type> list,
+                const allocator_type& allocator = allocator_type())
+      : InlinedVector(list.begin(), list.end(), allocator) {}
+
+  // Creates an inlined vector with elements constructed from the provided
+  // forward iterator range [`first`, `last`).
+  //
+  // NOTE: the `enable_if` prevents ambiguous interpretation between a call to
+  // this constructor with two integral arguments and a call to the above
+  // `InlinedVector(size_type, const_reference)` constructor.
+  template <typename ForwardIterator,
+            EnableIfAtLeastForwardIterator<ForwardIterator> = 0>
+  InlinedVector(ForwardIterator first, ForwardIterator last,
+                const allocator_type& allocator = allocator_type())
+      : storage_(allocator) {
+    storage_.Initialize(IteratorValueAdapter<A, ForwardIterator>(first),
+                        static_cast<size_t>(std::distance(first, last)));
+  }
+
+  // Creates an inlined vector with elements constructed from the provided input
+  // iterator range [`first`, `last`).
+  template <typename InputIterator,
+            DisableIfAtLeastForwardIterator<InputIterator> = 0>
+  InlinedVector(InputIterator first, InputIterator last,
+                const allocator_type& allocator = allocator_type())
+      : storage_(allocator) {
+    std::copy(first, last, std::back_inserter(*this));
+  }
+
+  // Creates an inlined vector by copying the contents of `other` using
+  // `other`'s allocator.
+  InlinedVector(const InlinedVector& other)
+      : InlinedVector(other, other.storage_.GetAllocator()) {}
+
+  // Creates an inlined vector by copying the contents of `other` using the
+  // provided `allocator`.
+  InlinedVector(const InlinedVector& other, const allocator_type& allocator)
+      : storage_(allocator) {
+    if (other.empty()) {
+      // Empty; nothing to do.
+    } else if (IsMemcpyOk<A>::value && !other.storage_.GetIsAllocated()) {
+      // Memcpy-able and do not need allocation.
+      storage_.MemcpyFrom(other.storage_);
+    } else {
+      storage_.InitFrom(other.storage_);
+    }
+  }
+
+  // Creates an inlined vector by moving in the contents of `other` without
+  // allocating. If `other` contains allocated memory, the newly-created inlined
+  // vector will take ownership of that memory. However, if `other` does not
+  // contain allocated memory, the newly-created inlined vector will perform
+  // element-wise move construction of the contents of `other`.
+  //
+  // NOTE: since no allocation is performed for the inlined vector in either
+  // case, the `noexcept(...)` specification depends on whether moving the
+  // underlying objects can throw. It is assumed assumed that...
+  //  a) move constructors should only throw due to allocation failure.
+  //  b) if `value_type`'s move constructor allocates, it uses the same
+  //     allocation function as the inlined vector's allocator.
+  // Thus, the move constructor is non-throwing if the allocator is non-throwing
+  // or `value_type`'s move constructor is specified as `noexcept`.
+  InlinedVector(InlinedVector&& other) noexcept(
+      absl::allocator_is_nothrow<allocator_type>::value ||
+      std::is_nothrow_move_constructible<value_type>::value)
+      : storage_(other.storage_.GetAllocator()) {
+    if (IsMemcpyOk<A>::value) {
+      storage_.MemcpyFrom(other.storage_);
+
+      other.storage_.SetInlinedSize(0);
+    } else if (other.storage_.GetIsAllocated()) {
+      storage_.SetAllocation({other.storage_.GetAllocatedData(),
+                              other.storage_.GetAllocatedCapacity()});
+      storage_.SetAllocatedSize(other.storage_.GetSize());
+
+      other.storage_.SetInlinedSize(0);
+    } else {
+      IteratorValueAdapter<A, MoveIterator<A>> other_values(
+          MoveIterator<A>(other.storage_.GetInlinedData()));
+
+      inlined_vector_internal::ConstructElements<A>(
+          storage_.GetAllocator(), storage_.GetInlinedData(), other_values,
+          other.storage_.GetSize());
+
+      storage_.SetInlinedSize(other.storage_.GetSize());
+    }
+  }
+
+  // Creates an inlined vector by moving in the contents of `other` with a copy
+  // of `allocator`.
+  //
+  // NOTE: if `other`'s allocator is not equal to `allocator`, even if `other`
+  // contains allocated memory, this move constructor will still allocate. Since
+  // allocation is performed, this constructor can only be `noexcept` if the
+  // specified allocator is also `noexcept`.
+  InlinedVector(
+      InlinedVector&& other,
+      const allocator_type&
+          allocator) noexcept(absl::allocator_is_nothrow<allocator_type>::value)
+      : storage_(allocator) {
+    if (IsMemcpyOk<A>::value) {
+      storage_.MemcpyFrom(other.storage_);
+
+      other.storage_.SetInlinedSize(0);
+    } else if ((storage_.GetAllocator() == other.storage_.GetAllocator()) &&
+               other.storage_.GetIsAllocated()) {
+      storage_.SetAllocation({other.storage_.GetAllocatedData(),
+                              other.storage_.GetAllocatedCapacity()});
+      storage_.SetAllocatedSize(other.storage_.GetSize());
+
+      other.storage_.SetInlinedSize(0);
+    } else {
+      storage_.Initialize(IteratorValueAdapter<A, MoveIterator<A>>(
+                              MoveIterator<A>(other.data())),
+                          other.size());
+    }
+  }
+
+  ~InlinedVector() {}
+
+  // ---------------------------------------------------------------------------
+  // InlinedVector Member Accessors
+  // ---------------------------------------------------------------------------
+
+  // `InlinedVector::empty()`
+  //
+  // Returns whether the inlined vector contains no elements.
+  bool empty() const noexcept { return !size(); }
+
+  // `InlinedVector::size()`
+  //
+  // Returns the number of elements in the inlined vector.
+  size_type size() const noexcept { return storage_.GetSize(); }
+
+  // `InlinedVector::max_size()`
+  //
+  // Returns the maximum number of elements the inlined vector can hold.
+  size_type max_size() const noexcept {
+    // One bit of the size storage is used to indicate whether the inlined
+    // vector contains allocated memory. As a result, the maximum size that the
+    // inlined vector can express is half of the max for `size_type`.
+    return (std::numeric_limits<size_type>::max)() / 2;
+  }
+
+  // `InlinedVector::capacity()`
+  //
+  // Returns the number of elements that could be stored in the inlined vector
+  // without requiring a reallocation.
+  //
+  // NOTE: for most inlined vectors, `capacity()` should be equal to the
+  // template parameter `N`. For inlined vectors which exceed this capacity,
+  // they will no longer be inlined and `capacity()` will equal the capactity of
+  // the allocated memory.
+  size_type capacity() const noexcept {
+    return storage_.GetIsAllocated() ? storage_.GetAllocatedCapacity()
+                                     : storage_.GetInlinedCapacity();
+  }
+
+  // `InlinedVector::data()`
+  //
+  // Returns a `pointer` to the elements of the inlined vector. This pointer
+  // can be used to access and modify the contained elements.
+  //
+  // NOTE: only elements within [`data()`, `data() + size()`) are valid.
+  pointer data() noexcept {
+    return storage_.GetIsAllocated() ? storage_.GetAllocatedData()
+                                     : storage_.GetInlinedData();
+  }
+
+  // Overload of `InlinedVector::data()` that returns a `const_pointer` to the
+  // elements of the inlined vector. This pointer can be used to access but not
+  // modify the contained elements.
+  //
+  // NOTE: only elements within [`data()`, `data() + size()`) are valid.
+  const_pointer data() const noexcept {
+    return storage_.GetIsAllocated() ? storage_.GetAllocatedData()
+                                     : storage_.GetInlinedData();
+  }
+
+  // `InlinedVector::operator[](...)`
+  //
+  // Returns a `reference` to the `i`th element of the inlined vector.
+  reference operator[](size_type i) {
+    ABSL_HARDENING_ASSERT(i < size());
+    return data()[i];
+  }
+
+  // Overload of `InlinedVector::operator[](...)` that returns a
+  // `const_reference` to the `i`th element of the inlined vector.
+  const_reference operator[](size_type i) const {
+    ABSL_HARDENING_ASSERT(i < size());
+    return data()[i];
+  }
+
+  // `InlinedVector::at(...)`
+  //
+  // Returns a `reference` to the `i`th element of the inlined vector.
+  //
+  // NOTE: if `i` is not within the required range of `InlinedVector::at(...)`,
+  // in both debug and non-debug builds, `std::out_of_range` will be thrown.
+  reference at(size_type i) {
+    if (ABSL_PREDICT_FALSE(i >= size())) {
+      base_internal::ThrowStdOutOfRange(
+          "`InlinedVector::at(size_type)` failed bounds check");
+    }
+    return data()[i];
+  }
+
+  // Overload of `InlinedVector::at(...)` that returns a `const_reference` to
+  // the `i`th element of the inlined vector.
+  //
+  // NOTE: if `i` is not within the required range of `InlinedVector::at(...)`,
+  // in both debug and non-debug builds, `std::out_of_range` will be thrown.
+  const_reference at(size_type i) const {
+    if (ABSL_PREDICT_FALSE(i >= size())) {
+      base_internal::ThrowStdOutOfRange(
+          "`InlinedVector::at(size_type) const` failed bounds check");
+    }
+    return data()[i];
+  }
+
+  // `InlinedVector::front()`
+  //
+  // Returns a `reference` to the first element of the inlined vector.
+  reference front() {
+    ABSL_HARDENING_ASSERT(!empty());
+    return data()[0];
+  }
+
+  // Overload of `InlinedVector::front()` that returns a `const_reference` to
+  // the first element of the inlined vector.
+  const_reference front() const {
+    ABSL_HARDENING_ASSERT(!empty());
+    return data()[0];
+  }
+
+  // `InlinedVector::back()`
+  //
+  // Returns a `reference` to the last element of the inlined vector.
+  reference back() {
+    ABSL_HARDENING_ASSERT(!empty());
+    return data()[size() - 1];
+  }
+
+  // Overload of `InlinedVector::back()` that returns a `const_reference` to the
+  // last element of the inlined vector.
+  const_reference back() const {
+    ABSL_HARDENING_ASSERT(!empty());
+    return data()[size() - 1];
+  }
+
+  // `InlinedVector::begin()`
+  //
+  // Returns an `iterator` to the beginning of the inlined vector.
+  iterator begin() noexcept { return data(); }
+
+  // Overload of `InlinedVector::begin()` that returns a `const_iterator` to
+  // the beginning of the inlined vector.
+  const_iterator begin() const noexcept { return data(); }
+
+  // `InlinedVector::end()`
+  //
+  // Returns an `iterator` to the end of the inlined vector.
+  iterator end() noexcept { return data() + size(); }
+
+  // Overload of `InlinedVector::end()` that returns a `const_iterator` to the
+  // end of the inlined vector.
+  const_iterator end() const noexcept { return data() + size(); }
+
+  // `InlinedVector::cbegin()`
+  //
+  // Returns a `const_iterator` to the beginning of the inlined vector.
+  const_iterator cbegin() const noexcept { return begin(); }
+
+  // `InlinedVector::cend()`
+  //
+  // Returns a `const_iterator` to the end of the inlined vector.
+  const_iterator cend() const noexcept { return end(); }
+
+  // `InlinedVector::rbegin()`
+  //
+  // Returns a `reverse_iterator` from the end of the inlined vector.
+  reverse_iterator rbegin() noexcept { return reverse_iterator(end()); }
+
+  // Overload of `InlinedVector::rbegin()` that returns a
+  // `const_reverse_iterator` from the end of the inlined vector.
+  const_reverse_iterator rbegin() const noexcept {
+    return const_reverse_iterator(end());
+  }
+
+  // `InlinedVector::rend()`
+  //
+  // Returns a `reverse_iterator` from the beginning of the inlined vector.
+  reverse_iterator rend() noexcept { return reverse_iterator(begin()); }
+
+  // Overload of `InlinedVector::rend()` that returns a `const_reverse_iterator`
+  // from the beginning of the inlined vector.
+  const_reverse_iterator rend() const noexcept {
+    return const_reverse_iterator(begin());
+  }
+
+  // `InlinedVector::crbegin()`
+  //
+  // Returns a `const_reverse_iterator` from the end of the inlined vector.
+  const_reverse_iterator crbegin() const noexcept { return rbegin(); }
+
+  // `InlinedVector::crend()`
+  //
+  // Returns a `const_reverse_iterator` from the beginning of the inlined
+  // vector.
+  const_reverse_iterator crend() const noexcept { return rend(); }
+
+  // `InlinedVector::get_allocator()`
+  //
+  // Returns a copy of the inlined vector's allocator.
+  allocator_type get_allocator() const { return storage_.GetAllocator(); }
+
+  // ---------------------------------------------------------------------------
+  // InlinedVector Member Mutators
+  // ---------------------------------------------------------------------------
+
+  // `InlinedVector::operator=(...)`
+  //
+  // Replaces the elements of the inlined vector with copies of the elements of
+  // `list`.
+  InlinedVector& operator=(std::initializer_list<value_type> list) {
+    assign(list.begin(), list.end());
+
+    return *this;
+  }
+
+  // Overload of `InlinedVector::operator=(...)` that replaces the elements of
+  // the inlined vector with copies of the elements of `other`.
+  InlinedVector& operator=(const InlinedVector& other) {
+    if (ABSL_PREDICT_TRUE(this != std::addressof(other))) {
+      const_pointer other_data = other.data();
+      assign(other_data, other_data + other.size());
+    }
+
+    return *this;
+  }
+
+  // Overload of `InlinedVector::operator=(...)` that moves the elements of
+  // `other` into the inlined vector.
+  //
+  // NOTE: as a result of calling this overload, `other` is left in a valid but
+  // unspecified state.
+  InlinedVector& operator=(InlinedVector&& other) {
+    if (ABSL_PREDICT_TRUE(this != std::addressof(other))) {
+      if (IsMemcpyOk<A>::value || other.storage_.GetIsAllocated()) {
+        inlined_vector_internal::DestroyAdapter<A>::DestroyElements(
+            storage_.GetAllocator(), data(), size());
+        storage_.DeallocateIfAllocated();
+        storage_.MemcpyFrom(other.storage_);
+
+        other.storage_.SetInlinedSize(0);
+      } else {
+        storage_.Assign(IteratorValueAdapter<A, MoveIterator<A>>(
+                            MoveIterator<A>(other.storage_.GetInlinedData())),
+                        other.size());
+      }
+    }
+
+    return *this;
+  }
+
+  // `InlinedVector::assign(...)`
+  //
+  // Replaces the contents of the inlined vector with `n` copies of `v`.
+  void assign(size_type n, const_reference v) {
+    storage_.Assign(CopyValueAdapter<A>(std::addressof(v)), n);
+  }
+
+  // Overload of `InlinedVector::assign(...)` that replaces the contents of the
+  // inlined vector with copies of the elements of `list`.
+  void assign(std::initializer_list<value_type> list) {
+    assign(list.begin(), list.end());
+  }
+
+  // Overload of `InlinedVector::assign(...)` to replace the contents of the
+  // inlined vector with the range [`first`, `last`).
+  //
+  // NOTE: this overload is for iterators that are "forward" category or better.
+  template <typename ForwardIterator,
+            EnableIfAtLeastForwardIterator<ForwardIterator> = 0>
+  void assign(ForwardIterator first, ForwardIterator last) {
+    storage_.Assign(IteratorValueAdapter<A, ForwardIterator>(first),
+                    static_cast<size_t>(std::distance(first, last)));
+  }
+
+  // Overload of `InlinedVector::assign(...)` to replace the contents of the
+  // inlined vector with the range [`first`, `last`).
+  //
+  // NOTE: this overload is for iterators that are "input" category.
+  template <typename InputIterator,
+            DisableIfAtLeastForwardIterator<InputIterator> = 0>
+  void assign(InputIterator first, InputIterator last) {
+    size_type i = 0;
+    for (; i < size() && first != last; ++i, static_cast<void>(++first)) {
+      data()[i] = *first;
+    }
+
+    erase(data() + i, data() + size());
+    std::copy(first, last, std::back_inserter(*this));
+  }
+
+  // `InlinedVector::resize(...)`
+  //
+  // Resizes the inlined vector to contain `n` elements.
+  //
+  // NOTE: If `n` is smaller than `size()`, extra elements are destroyed. If `n`
+  // is larger than `size()`, new elements are value-initialized.
+  void resize(size_type n) {
+    ABSL_HARDENING_ASSERT(n <= max_size());
+    storage_.Resize(DefaultValueAdapter<A>(), n);
+  }
+
+  // Overload of `InlinedVector::resize(...)` that resizes the inlined vector to
+  // contain `n` elements.
+  //
+  // NOTE: if `n` is smaller than `size()`, extra elements are destroyed. If `n`
+  // is larger than `size()`, new elements are copied-constructed from `v`.
+  void resize(size_type n, const_reference v) {
+    ABSL_HARDENING_ASSERT(n <= max_size());
+    storage_.Resize(CopyValueAdapter<A>(std::addressof(v)), n);
+  }
+
+  // `InlinedVector::insert(...)`
+  //
+  // Inserts a copy of `v` at `pos`, returning an `iterator` to the newly
+  // inserted element.
+  iterator insert(const_iterator pos, const_reference v) {
+    return emplace(pos, v);
+  }
+
+  // Overload of `InlinedVector::insert(...)` that inserts `v` at `pos` using
+  // move semantics, returning an `iterator` to the newly inserted element.
+  iterator insert(const_iterator pos, value_type&& v) {
+    return emplace(pos, std::move(v));
+  }
+
+  // Overload of `InlinedVector::insert(...)` that inserts `n` contiguous copies
+  // of `v` starting at `pos`, returning an `iterator` pointing to the first of
+  // the newly inserted elements.
+  iterator insert(const_iterator pos, size_type n, const_reference v) {
+    ABSL_HARDENING_ASSERT(pos >= begin());
+    ABSL_HARDENING_ASSERT(pos <= end());
+
+    if (ABSL_PREDICT_TRUE(n != 0)) {
+      value_type dealias = v;
+      // https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102329#c2
+      // It appears that GCC thinks that since `pos` is a const pointer and may
+      // point to uninitialized memory at this point, a warning should be
+      // issued. But `pos` is actually only used to compute an array index to
+      // write to.
+#if !defined(__clang__) && defined(__GNUC__)
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wmaybe-uninitialized"
+#endif
+      return storage_.Insert(pos, CopyValueAdapter<A>(std::addressof(dealias)),
+                             n);
+#if !defined(__clang__) && defined(__GNUC__)
+#pragma GCC diagnostic pop
+#endif
+    } else {
+      return const_cast<iterator>(pos);
+    }
+  }
+
+  // Overload of `InlinedVector::insert(...)` that inserts copies of the
+  // elements of `list` starting at `pos`, returning an `iterator` pointing to
+  // the first of the newly inserted elements.
+  iterator insert(const_iterator pos, std::initializer_list<value_type> list) {
+    return insert(pos, list.begin(), list.end());
+  }
+
+  // Overload of `InlinedVector::insert(...)` that inserts the range [`first`,
+  // `last`) starting at `pos`, returning an `iterator` pointing to the first
+  // of the newly inserted elements.
+  //
+  // NOTE: this overload is for iterators that are "forward" category or better.
+  template <typename ForwardIterator,
+            EnableIfAtLeastForwardIterator<ForwardIterator> = 0>
+  iterator insert(const_iterator pos, ForwardIterator first,
+                  ForwardIterator last) {
+    ABSL_HARDENING_ASSERT(pos >= begin());
+    ABSL_HARDENING_ASSERT(pos <= end());
+
+    if (ABSL_PREDICT_TRUE(first != last)) {
+      return storage_.Insert(pos,
+                             IteratorValueAdapter<A, ForwardIterator>(first),
+                             std::distance(first, last));
+    } else {
+      return const_cast<iterator>(pos);
+    }
+  }
+
+  // Overload of `InlinedVector::insert(...)` that inserts the range [`first`,
+  // `last`) starting at `pos`, returning an `iterator` pointing to the first
+  // of the newly inserted elements.
+  //
+  // NOTE: this overload is for iterators that are "input" category.
+  template <typename InputIterator,
+            DisableIfAtLeastForwardIterator<InputIterator> = 0>
+  iterator insert(const_iterator pos, InputIterator first, InputIterator last) {
+    ABSL_HARDENING_ASSERT(pos >= begin());
+    ABSL_HARDENING_ASSERT(pos <= end());
+
+    size_type index = std::distance(cbegin(), pos);
+    for (size_type i = index; first != last; ++i, static_cast<void>(++first)) {
+      insert(data() + i, *first);
+    }
+
+    return iterator(data() + index);
+  }
+
+  // `InlinedVector::emplace(...)`
+  //
+  // Constructs and inserts an element using `args...` in the inlined vector at
+  // `pos`, returning an `iterator` pointing to the newly emplaced element.
+  template <typename... Args>
+  iterator emplace(const_iterator pos, Args&&... args) {
+    ABSL_HARDENING_ASSERT(pos >= begin());
+    ABSL_HARDENING_ASSERT(pos <= end());
+
+    value_type dealias(std::forward<Args>(args)...);
+    return storage_.Insert(pos,
+                           IteratorValueAdapter<A, MoveIterator<A>>(
+                               MoveIterator<A>(std::addressof(dealias))),
+                           1);
+  }
+
+  // `InlinedVector::emplace_back(...)`
+  //
+  // Constructs and inserts an element using `args...` in the inlined vector at
+  // `end()`, returning a `reference` to the newly emplaced element.
+  template <typename... Args>
+  reference emplace_back(Args&&... args) {
+    return storage_.EmplaceBack(std::forward<Args>(args)...);
+  }
+
+  // `InlinedVector::push_back(...)`
+  //
+  // Inserts a copy of `v` in the inlined vector at `end()`.
+  void push_back(const_reference v) { static_cast<void>(emplace_back(v)); }
+
+  // Overload of `InlinedVector::push_back(...)` for inserting `v` at `end()`
+  // using move semantics.
+  void push_back(value_type&& v) {
+    static_cast<void>(emplace_back(std::move(v)));
+  }
+
+  // `InlinedVector::pop_back()`
+  //
+  // Destroys the element at `back()`, reducing the size by `1`.
+  void pop_back() noexcept {
+    ABSL_HARDENING_ASSERT(!empty());
+
+    AllocatorTraits<A>::destroy(storage_.GetAllocator(), data() + (size() - 1));
+    storage_.SubtractSize(1);
+  }
+
+  // `InlinedVector::erase(...)`
+  //
+  // Erases the element at `pos`, returning an `iterator` pointing to where the
+  // erased element was located.
+  //
+  // NOTE: may return `end()`, which is not dereferencable.
+  iterator erase(const_iterator pos) {
+    ABSL_HARDENING_ASSERT(pos >= begin());
+    ABSL_HARDENING_ASSERT(pos < end());
+
+    return storage_.Erase(pos, pos + 1);
+  }
+
+  // Overload of `InlinedVector::erase(...)` that erases every element in the
+  // range [`from`, `to`), returning an `iterator` pointing to where the first
+  // erased element was located.
+  //
+  // NOTE: may return `end()`, which is not dereferencable.
+  iterator erase(const_iterator from, const_iterator to) {
+    ABSL_HARDENING_ASSERT(from >= begin());
+    ABSL_HARDENING_ASSERT(from <= to);
+    ABSL_HARDENING_ASSERT(to <= end());
+
+    if (ABSL_PREDICT_TRUE(from != to)) {
+      return storage_.Erase(from, to);
+    } else {
+      return const_cast<iterator>(from);
+    }
+  }
+
+  // `InlinedVector::clear()`
+  //
+  // Destroys all elements in the inlined vector, setting the size to `0` and
+  // deallocating any held memory.
+  void clear() noexcept {
+    inlined_vector_internal::DestroyAdapter<A>::DestroyElements(
+        storage_.GetAllocator(), data(), size());
+    storage_.DeallocateIfAllocated();
+
+    storage_.SetInlinedSize(0);
+  }
+
+  // `InlinedVector::reserve(...)`
+  //
+  // Ensures that there is enough room for at least `n` elements.
+  void reserve(size_type n) { storage_.Reserve(n); }
+
+  // `InlinedVector::shrink_to_fit()`
+  //
+  // Attempts to reduce memory usage by moving elements to (or keeping elements
+  // in) the smallest available buffer sufficient for containing `size()`
+  // elements.
+  //
+  // If `size()` is sufficiently small, the elements will be moved into (or kept
+  // in) the inlined space.
+  void shrink_to_fit() {
+    if (storage_.GetIsAllocated()) {
+      storage_.ShrinkToFit();
+    }
+  }
+
+  // `InlinedVector::swap(...)`
+  //
+  // Swaps the contents of the inlined vector with `other`.
+  void swap(InlinedVector& other) {
+    if (ABSL_PREDICT_TRUE(this != std::addressof(other))) {
+      storage_.Swap(std::addressof(other.storage_));
+    }
+  }
+
+ private:
+  template <typename H, typename TheT, size_t TheN, typename TheA>
+  friend H AbslHashValue(H h, const absl::InlinedVector<TheT, TheN, TheA>& a);
+
+  Storage storage_;
+};
+
+// -----------------------------------------------------------------------------
+// InlinedVector Non-Member Functions
+// -----------------------------------------------------------------------------
+
+// `swap(...)`
+//
+// Swaps the contents of two inlined vectors.
+template <typename T, size_t N, typename A>
+void swap(absl::InlinedVector<T, N, A>& a,
+          absl::InlinedVector<T, N, A>& b) noexcept(noexcept(a.swap(b))) {
+  a.swap(b);
+}
+
+// `operator==(...)`
+//
+// Tests for value-equality of two inlined vectors.
+template <typename T, size_t N, typename A>
+bool operator==(const absl::InlinedVector<T, N, A>& a,
+                const absl::InlinedVector<T, N, A>& b) {
+  auto a_data = a.data();
+  auto b_data = b.data();
+  return absl::equal(a_data, a_data + a.size(), b_data, b_data + b.size());
+}
+
+// `operator!=(...)`
+//
+// Tests for value-inequality of two inlined vectors.
+template <typename T, size_t N, typename A>
+bool operator!=(const absl::InlinedVector<T, N, A>& a,
+                const absl::InlinedVector<T, N, A>& b) {
+  return !(a == b);
+}
+
+// `operator<(...)`
+//
+// Tests whether the value of an inlined vector is less than the value of
+// another inlined vector using a lexicographical comparison algorithm.
+template <typename T, size_t N, typename A>
+bool operator<(const absl::InlinedVector<T, N, A>& a,
+               const absl::InlinedVector<T, N, A>& b) {
+  auto a_data = a.data();
+  auto b_data = b.data();
+  return std::lexicographical_compare(a_data, a_data + a.size(), b_data,
+                                      b_data + b.size());
+}
+
+// `operator>(...)`
+//
+// Tests whether the value of an inlined vector is greater than the value of
+// another inlined vector using a lexicographical comparison algorithm.
+template <typename T, size_t N, typename A>
+bool operator>(const absl::InlinedVector<T, N, A>& a,
+               const absl::InlinedVector<T, N, A>& b) {
+  return b < a;
+}
+
+// `operator<=(...)`
+//
+// Tests whether the value of an inlined vector is less than or equal to the
+// value of another inlined vector using a lexicographical comparison algorithm.
+template <typename T, size_t N, typename A>
+bool operator<=(const absl::InlinedVector<T, N, A>& a,
+                const absl::InlinedVector<T, N, A>& b) {
+  return !(b < a);
+}
+
+// `operator>=(...)`
+//
+// Tests whether the value of an inlined vector is greater than or equal to the
+// value of another inlined vector using a lexicographical comparison algorithm.
+template <typename T, size_t N, typename A>
+bool operator>=(const absl::InlinedVector<T, N, A>& a,
+                const absl::InlinedVector<T, N, A>& b) {
+  return !(a < b);
+}
+
+// `AbslHashValue(...)`
+//
+// Provides `absl::Hash` support for `absl::InlinedVector`. It is uncommon to
+// call this directly.
+template <typename H, typename T, size_t N, typename A>
+H AbslHashValue(H h, const absl::InlinedVector<T, N, A>& a) {
+  auto size = a.size();
+  return H::combine(H::combine_contiguous(std::move(h), a.data(), size), size);
+}
+
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_CONTAINER_INLINED_VECTOR_H_
--- a/include/absl/container/internal/btree.h
+++ b/include/absl/container/internal/btree.h
--- a/include/absl/container/internal/btree_container.h
+++ b/include/absl/container/internal/btree_container.h
@ -0,0 +1,699 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef ABSL_CONTAINER_INTERNAL_BTREE_CONTAINER_H_
+#define ABSL_CONTAINER_INTERNAL_BTREE_CONTAINER_H_
+
+#include <algorithm>
+#include <initializer_list>
+#include <iterator>
+#include <utility>
+
+#include "absl/base/attributes.h"
+#include "absl/base/internal/throw_delegate.h"
+#include "absl/container/internal/btree.h"  // IWYU pragma: export
+#include "absl/container/internal/common.h"
+#include "absl/memory/memory.h"
+#include "absl/meta/type_traits.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace container_internal {
+
+// A common base class for btree_set, btree_map, btree_multiset, and
+// btree_multimap.
+template <typename Tree>
+class btree_container {
+  using params_type = typename Tree::params_type;
+
+ protected:
+  // Alias used for heterogeneous lookup functions.
+  // `key_arg<K>` evaluates to `K` when the functors are transparent and to
+  // `key_type` otherwise. It permits template argument deduction on `K` for the
+  // transparent case.
+  template <class K>
+  using key_arg =
+      typename KeyArg<params_type::kIsKeyCompareTransparent>::template type<
+          K, typename Tree::key_type>;
+
+ public:
+  using key_type = typename Tree::key_type;
+  using value_type = typename Tree::value_type;
+  using size_type = typename Tree::size_type;
+  using difference_type = typename Tree::difference_type;
+  using key_compare = typename Tree::original_key_compare;
+  using value_compare = typename Tree::value_compare;
+  using allocator_type = typename Tree::allocator_type;
+  using reference = typename Tree::reference;
+  using const_reference = typename Tree::const_reference;
+  using pointer = typename Tree::pointer;
+  using const_pointer = typename Tree::const_pointer;
+  using iterator = typename Tree::iterator;
+  using const_iterator = typename Tree::const_iterator;
+  using reverse_iterator = typename Tree::reverse_iterator;
+  using const_reverse_iterator = typename Tree::const_reverse_iterator;
+  using node_type = typename Tree::node_handle_type;
+
+  // Constructors/assignments.
+  btree_container() : tree_(key_compare(), allocator_type()) {}
+  explicit btree_container(const key_compare &comp,
+                           const allocator_type &alloc = allocator_type())
+      : tree_(comp, alloc) {}
+  explicit btree_container(const allocator_type &alloc)
+      : tree_(key_compare(), alloc) {}
+
+  btree_container(const btree_container &other)
+      : btree_container(other, absl::allocator_traits<allocator_type>::
+                                   select_on_container_copy_construction(
+                                       other.get_allocator())) {}
+  btree_container(const btree_container &other, const allocator_type &alloc)
+      : tree_(other.tree_, alloc) {}
+
+  btree_container(btree_container &&other) noexcept(
+      std::is_nothrow_move_constructible<Tree>::value) = default;
+  btree_container(btree_container &&other, const allocator_type &alloc)
+      : tree_(std::move(other.tree_), alloc) {}
+
+  btree_container &operator=(const btree_container &other) = default;
+  btree_container &operator=(btree_container &&other) noexcept(
+      std::is_nothrow_move_assignable<Tree>::value) = default;
+
+  // Iterator routines.
+  iterator begin() { return tree_.begin(); }
+  const_iterator begin() const { return tree_.begin(); }
+  const_iterator cbegin() const { return tree_.begin(); }
+  iterator end() { return tree_.end(); }
+  const_iterator end() const { return tree_.end(); }
+  const_iterator cend() const { return tree_.end(); }
+  reverse_iterator rbegin() { return tree_.rbegin(); }
+  const_reverse_iterator rbegin() const { return tree_.rbegin(); }
+  const_reverse_iterator crbegin() const { return tree_.rbegin(); }
+  reverse_iterator rend() { return tree_.rend(); }
+  const_reverse_iterator rend() const { return tree_.rend(); }
+  const_reverse_iterator crend() const { return tree_.rend(); }
+
+  // Lookup routines.
+  template <typename K = key_type>
+  size_type count(const key_arg<K> &key) const {
+    auto equal_range = this->equal_range(key);
+    return std::distance(equal_range.first, equal_range.second);
+  }
+  template <typename K = key_type>
+  iterator find(const key_arg<K> &key) {
+    return tree_.find(key);
+  }
+  template <typename K = key_type>
+  const_iterator find(const key_arg<K> &key) const {
+    return tree_.find(key);
+  }
+  template <typename K = key_type>
+  bool contains(const key_arg<K> &key) const {
+    return find(key) != end();
+  }
+  template <typename K = key_type>
+  iterator lower_bound(const key_arg<K> &key) {
+    return tree_.lower_bound(key);
+  }
+  template <typename K = key_type>
+  const_iterator lower_bound(const key_arg<K> &key) const {
+    return tree_.lower_bound(key);
+  }
+  template <typename K = key_type>
+  iterator upper_bound(const key_arg<K> &key) {
+    return tree_.upper_bound(key);
+  }
+  template <typename K = key_type>
+  const_iterator upper_bound(const key_arg<K> &key) const {
+    return tree_.upper_bound(key);
+  }
+  template <typename K = key_type>
+  std::pair<iterator, iterator> equal_range(const key_arg<K> &key) {
+    return tree_.equal_range(key);
+  }
+  template <typename K = key_type>
+  std::pair<const_iterator, const_iterator> equal_range(
+      const key_arg<K> &key) const {
+    return tree_.equal_range(key);
+  }
+
+  // Deletion routines. Note that there is also a deletion routine that is
+  // specific to btree_set_container/btree_multiset_container.
+
+  // Erase the specified iterator from the btree. The iterator must be valid
+  // (i.e. not equal to end()).  Return an iterator pointing to the node after
+  // the one that was erased (or end() if none exists).
+  iterator erase(const_iterator iter) { return tree_.erase(iterator(iter)); }
+  iterator erase(iterator iter) { return tree_.erase(iter); }
+  iterator erase(const_iterator first, const_iterator last) {
+    return tree_.erase_range(iterator(first), iterator(last)).second;
+  }
+  template <typename K = key_type>
+  size_type erase(const key_arg<K> &key) {
+    auto equal_range = this->equal_range(key);
+    return tree_.erase_range(equal_range.first, equal_range.second).first;
+  }
+
+  // Extract routines.
+  node_type extract(iterator position) {
+    // Use Construct instead of Transfer because the rebalancing code will
+    // destroy the slot later.
+    auto node =
+        CommonAccess::Construct<node_type>(get_allocator(), position.slot());
+    erase(position);
+    return node;
+  }
+  node_type extract(const_iterator position) {
+    return extract(iterator(position));
+  }
+
+  // Utility routines.
+  ABSL_ATTRIBUTE_REINITIALIZES void clear() { tree_.clear(); }
+  void swap(btree_container &other) { tree_.swap(other.tree_); }
+  void verify() const { tree_.verify(); }
+
+  // Size routines.
+  size_type size() const { return tree_.size(); }
+  size_type max_size() const { return tree_.max_size(); }
+  bool empty() const { return tree_.empty(); }
+
+  friend bool operator==(const btree_container &x, const btree_container &y) {
+    if (x.size() != y.size()) return false;
+    return std::equal(x.begin(), x.end(), y.begin());
+  }
+
+  friend bool operator!=(const btree_container &x, const btree_container &y) {
+    return !(x == y);
+  }
+
+  friend bool operator<(const btree_container &x, const btree_container &y) {
+    return std::lexicographical_compare(x.begin(), x.end(), y.begin(), y.end());
+  }
+
+  friend bool operator>(const btree_container &x, const btree_container &y) {
+    return y < x;
+  }
+
+  friend bool operator<=(const btree_container &x, const btree_container &y) {
+    return !(y < x);
+  }
+
+  friend bool operator>=(const btree_container &x, const btree_container &y) {
+    return !(x < y);
+  }
+
+  // The allocator used by the btree.
+  allocator_type get_allocator() const { return tree_.get_allocator(); }
+
+  // The key comparator used by the btree.
+  key_compare key_comp() const { return key_compare(tree_.key_comp()); }
+  value_compare value_comp() const { return tree_.value_comp(); }
+
+  // Support absl::Hash.
+  template <typename State>
+  friend State AbslHashValue(State h, const btree_container &b) {
+    for (const auto &v : b) {
+      h = State::combine(std::move(h), v);
+    }
+    return State::combine(std::move(h), b.size());
+  }
+
+ protected:
+  friend struct btree_access;
+  Tree tree_;
+};
+
+// A common base class for btree_set and btree_map.
+template <typename Tree>
+class btree_set_container : public btree_container<Tree> {
+  using super_type = btree_container<Tree>;
+  using params_type = typename Tree::params_type;
+  using init_type = typename params_type::init_type;
+  using is_key_compare_to = typename params_type::is_key_compare_to;
+  friend class BtreeNodePeer;
+
+ protected:
+  template <class K>
+  using key_arg = typename super_type::template key_arg<K>;
+
+ public:
+  using key_type = typename Tree::key_type;
+  using value_type = typename Tree::value_type;
+  using size_type = typename Tree::size_type;
+  using key_compare = typename Tree::original_key_compare;
+  using allocator_type = typename Tree::allocator_type;
+  using iterator = typename Tree::iterator;
+  using const_iterator = typename Tree::const_iterator;
+  using node_type = typename super_type::node_type;
+  using insert_return_type = InsertReturnType<iterator, node_type>;
+
+  // Inherit constructors.
+  using super_type::super_type;
+  btree_set_container() {}
+
+  // Range constructors.
+  template <class InputIterator>
+  btree_set_container(InputIterator b, InputIterator e,
+                      const key_compare &comp = key_compare(),
+                      const allocator_type &alloc = allocator_type())
+      : super_type(comp, alloc) {
+    insert(b, e);
+  }
+  template <class InputIterator>
+  btree_set_container(InputIterator b, InputIterator e,
+                      const allocator_type &alloc)
+      : btree_set_container(b, e, key_compare(), alloc) {}
+
+  // Initializer list constructors.
+  btree_set_container(std::initializer_list<init_type> init,
+                      const key_compare &comp = key_compare(),
+                      const allocator_type &alloc = allocator_type())
+      : btree_set_container(init.begin(), init.end(), comp, alloc) {}
+  btree_set_container(std::initializer_list<init_type> init,
+                      const allocator_type &alloc)
+      : btree_set_container(init.begin(), init.end(), alloc) {}
+
+  // Insertion routines.
+  std::pair<iterator, bool> insert(const value_type &v) {
+    return this->tree_.insert_unique(params_type::key(v), v);
+  }
+  std::pair<iterator, bool> insert(value_type &&v) {
+    return this->tree_.insert_unique(params_type::key(v), std::move(v));
+  }
+  template <typename... Args>
+  std::pair<iterator, bool> emplace(Args &&... args) {
+    // Use a node handle to manage a temp slot.
+    auto node = CommonAccess::Construct<node_type>(this->get_allocator(),
+                                                   std::forward<Args>(args)...);
+    auto *slot = CommonAccess::GetSlot(node);
+    return this->tree_.insert_unique(params_type::key(slot), slot);
+  }
+  iterator insert(const_iterator hint, const value_type &v) {
+    return this->tree_
+        .insert_hint_unique(iterator(hint), params_type::key(v), v)
+        .first;
+  }
+  iterator insert(const_iterator hint, value_type &&v) {
+    return this->tree_
+        .insert_hint_unique(iterator(hint), params_type::key(v), std::move(v))
+        .first;
+  }
+  template <typename... Args>
+  iterator emplace_hint(const_iterator hint, Args &&... args) {
+    // Use a node handle to manage a temp slot.
+    auto node = CommonAccess::Construct<node_type>(this->get_allocator(),
+                                                   std::forward<Args>(args)...);
+    auto *slot = CommonAccess::GetSlot(node);
+    return this->tree_
+        .insert_hint_unique(iterator(hint), params_type::key(slot), slot)
+        .first;
+  }
+  template <typename InputIterator>
+  void insert(InputIterator b, InputIterator e) {
+    this->tree_.insert_iterator_unique(b, e, 0);
+  }
+  void insert(std::initializer_list<init_type> init) {
+    this->tree_.insert_iterator_unique(init.begin(), init.end(), 0);
+  }
+  insert_return_type insert(node_type &&node) {
+    if (!node) return {this->end(), false, node_type()};
+    std::pair<iterator, bool> res =
+        this->tree_.insert_unique(params_type::key(CommonAccess::GetSlot(node)),
+                                  CommonAccess::GetSlot(node));
+    if (res.second) {
+      CommonAccess::Destroy(&node);
+      return {res.first, true, node_type()};
+    } else {
+      return {res.first, false, std::move(node)};
+    }
+  }
+  iterator insert(const_iterator hint, node_type &&node) {
+    if (!node) return this->end();
+    std::pair<iterator, bool> res = this->tree_.insert_hint_unique(
+        iterator(hint), params_type::key(CommonAccess::GetSlot(node)),
+        CommonAccess::GetSlot(node));
+    if (res.second) CommonAccess::Destroy(&node);
+    return res.first;
+  }
+
+  // Node extraction routines.
+  template <typename K = key_type>
+  node_type extract(const key_arg<K> &key) {
+    const std::pair<iterator, bool> lower_and_equal =
+        this->tree_.lower_bound_equal(key);
+    return lower_and_equal.second ? extract(lower_and_equal.first)
+                                  : node_type();
+  }
+  using super_type::extract;
+
+  // Merge routines.
+  // Moves elements from `src` into `this`. If the element already exists in
+  // `this`, it is left unmodified in `src`.
+  template <
+      typename T,
+      typename absl::enable_if_t<
+          absl::conjunction<
+              std::is_same<value_type, typename T::value_type>,
+              std::is_same<allocator_type, typename T::allocator_type>,
+              std::is_same<typename params_type::is_map_container,
+                           typename T::params_type::is_map_container>>::value,
+          int> = 0>
+  void merge(btree_container<T> &src) {  // NOLINT
+    for (auto src_it = src.begin(); src_it != src.end();) {
+      if (insert(std::move(params_type::element(src_it.slot()))).second) {
+        src_it = src.erase(src_it);
+      } else {
+        ++src_it;
+      }
+    }
+  }
+
+  template <
+      typename T,
+      typename absl::enable_if_t<
+          absl::conjunction<
+              std::is_same<value_type, typename T::value_type>,
+              std::is_same<allocator_type, typename T::allocator_type>,
+              std::is_same<typename params_type::is_map_container,
+                           typename T::params_type::is_map_container>>::value,
+          int> = 0>
+  void merge(btree_container<T> &&src) {
+    merge(src);
+  }
+};
+
+// Base class for btree_map.
+template <typename Tree>
+class btree_map_container : public btree_set_container<Tree> {
+  using super_type = btree_set_container<Tree>;
+  using params_type = typename Tree::params_type;
+  friend class BtreeNodePeer;
+
+ private:
+  template <class K>
+  using key_arg = typename super_type::template key_arg<K>;
+
+ public:
+  using key_type = typename Tree::key_type;
+  using mapped_type = typename params_type::mapped_type;
+  using value_type = typename Tree::value_type;
+  using key_compare = typename Tree::original_key_compare;
+  using allocator_type = typename Tree::allocator_type;
+  using iterator = typename Tree::iterator;
+  using const_iterator = typename Tree::const_iterator;
+
+  // Inherit constructors.
+  using super_type::super_type;
+  btree_map_container() {}
+
+  // Insertion routines.
+  // Note: the nullptr template arguments and extra `const M&` overloads allow
+  // for supporting bitfield arguments.
+  template <typename K = key_type, class M>
+  std::pair<iterator, bool> insert_or_assign(const key_arg<K> &k,
+                                             const M &obj) {
+    return insert_or_assign_impl(k, obj);
+  }
+  template <typename K = key_type, class M, K * = nullptr>
+  std::pair<iterator, bool> insert_or_assign(key_arg<K> &&k, const M &obj) {
+    return insert_or_assign_impl(std::forward<K>(k), obj);
+  }
+  template <typename K = key_type, class M, M * = nullptr>
+  std::pair<iterator, bool> insert_or_assign(const key_arg<K> &k, M &&obj) {
+    return insert_or_assign_impl(k, std::forward<M>(obj));
+  }
+  template <typename K = key_type, class M, K * = nullptr, M * = nullptr>
+  std::pair<iterator, bool> insert_or_assign(key_arg<K> &&k, M &&obj) {
+    return insert_or_assign_impl(std::forward<K>(k), std::forward<M>(obj));
+  }
+  template <typename K = key_type, class M>
+  iterator insert_or_assign(const_iterator hint, const key_arg<K> &k,
+                            const M &obj) {
+    return insert_or_assign_hint_impl(hint, k, obj);
+  }
+  template <typename K = key_type, class M, K * = nullptr>
+  iterator insert_or_assign(const_iterator hint, key_arg<K> &&k, const M &obj) {
+    return insert_or_assign_hint_impl(hint, std::forward<K>(k), obj);
+  }
+  template <typename K = key_type, class M, M * = nullptr>
+  iterator insert_or_assign(const_iterator hint, const key_arg<K> &k, M &&obj) {
+    return insert_or_assign_hint_impl(hint, k, std::forward<M>(obj));
+  }
+  template <typename K = key_type, class M, K * = nullptr, M * = nullptr>
+  iterator insert_or_assign(const_iterator hint, key_arg<K> &&k, M &&obj) {
+    return insert_or_assign_hint_impl(hint, std::forward<K>(k),
+                                      std::forward<M>(obj));
+  }
+
+  template <typename K = key_type, typename... Args,
+            typename absl::enable_if_t<
+                !std::is_convertible<K, const_iterator>::value, int> = 0>
+  std::pair<iterator, bool> try_emplace(const key_arg<K> &k, Args &&... args) {
+    return try_emplace_impl(k, std::forward<Args>(args)...);
+  }
+  template <typename K = key_type, typename... Args,
+            typename absl::enable_if_t<
+                !std::is_convertible<K, const_iterator>::value, int> = 0>
+  std::pair<iterator, bool> try_emplace(key_arg<K> &&k, Args &&... args) {
+    return try_emplace_impl(std::forward<K>(k), std::forward<Args>(args)...);
+  }
+  template <typename K = key_type, typename... Args>
+  iterator try_emplace(const_iterator hint, const key_arg<K> &k,
+                       Args &&... args) {
+    return try_emplace_hint_impl(hint, k, std::forward<Args>(args)...);
+  }
+  template <typename K = key_type, typename... Args>
+  iterator try_emplace(const_iterator hint, key_arg<K> &&k, Args &&... args) {
+    return try_emplace_hint_impl(hint, std::forward<K>(k),
+                                 std::forward<Args>(args)...);
+  }
+
+  template <typename K = key_type>
+  mapped_type &operator[](const key_arg<K> &k) {
+    return try_emplace(k).first->second;
+  }
+  template <typename K = key_type>
+  mapped_type &operator[](key_arg<K> &&k) {
+    return try_emplace(std::forward<K>(k)).first->second;
+  }
+
+  template <typename K = key_type>
+  mapped_type &at(const key_arg<K> &key) {
+    auto it = this->find(key);
+    if (it == this->end())
+      base_internal::ThrowStdOutOfRange("absl::btree_map::at");
+    return it->second;
+  }
+  template <typename K = key_type>
+  const mapped_type &at(const key_arg<K> &key) const {
+    auto it = this->find(key);
+    if (it == this->end())
+      base_internal::ThrowStdOutOfRange("absl::btree_map::at");
+    return it->second;
+  }
+
+ private:
+  // Note: when we call `std::forward<M>(obj)` twice, it's safe because
+  // insert_unique/insert_hint_unique are guaranteed to not consume `obj` when
+  // `ret.second` is false.
+  template <class K, class M>
+  std::pair<iterator, bool> insert_or_assign_impl(K &&k, M &&obj) {
+    const std::pair<iterator, bool> ret =
+        this->tree_.insert_unique(k, std::forward<K>(k), std::forward<M>(obj));
+    if (!ret.second) ret.first->second = std::forward<M>(obj);
+    return ret;
+  }
+  template <class K, class M>
+  iterator insert_or_assign_hint_impl(const_iterator hint, K &&k, M &&obj) {
+    const std::pair<iterator, bool> ret = this->tree_.insert_hint_unique(
+        iterator(hint), k, std::forward<K>(k), std::forward<M>(obj));
+    if (!ret.second) ret.first->second = std::forward<M>(obj);
+    return ret.first;
+  }
+
+  template <class K, class... Args>
+  std::pair<iterator, bool> try_emplace_impl(K &&k, Args &&... args) {
+    return this->tree_.insert_unique(
+        k, std::piecewise_construct, std::forward_as_tuple(std::forward<K>(k)),
+        std::forward_as_tuple(std::forward<Args>(args)...));
+  }
+  template <class K, class... Args>
+  iterator try_emplace_hint_impl(const_iterator hint, K &&k, Args &&... args) {
+    return this->tree_
+        .insert_hint_unique(iterator(hint), k, std::piecewise_construct,
+                            std::forward_as_tuple(std::forward<K>(k)),
+                            std::forward_as_tuple(std::forward<Args>(args)...))
+        .first;
+  }
+};
+
+// A common base class for btree_multiset and btree_multimap.
+template <typename Tree>
+class btree_multiset_container : public btree_container<Tree> {
+  using super_type = btree_container<Tree>;
+  using params_type = typename Tree::params_type;
+  using init_type = typename params_type::init_type;
+  using is_key_compare_to = typename params_type::is_key_compare_to;
+  friend class BtreeNodePeer;
+
+  template <class K>
+  using key_arg = typename super_type::template key_arg<K>;
+
+ public:
+  using key_type = typename Tree::key_type;
+  using value_type = typename Tree::value_type;
+  using size_type = typename Tree::size_type;
+  using key_compare = typename Tree::original_key_compare;
+  using allocator_type = typename Tree::allocator_type;
+  using iterator = typename Tree::iterator;
+  using const_iterator = typename Tree::const_iterator;
+  using node_type = typename super_type::node_type;
+
+  // Inherit constructors.
+  using super_type::super_type;
+  btree_multiset_container() {}
+
+  // Range constructors.
+  template <class InputIterator>
+  btree_multiset_container(InputIterator b, InputIterator e,
+                           const key_compare &comp = key_compare(),
+                           const allocator_type &alloc = allocator_type())
+      : super_type(comp, alloc) {
+    insert(b, e);
+  }
+  template <class InputIterator>
+  btree_multiset_container(InputIterator b, InputIterator e,
+                           const allocator_type &alloc)
+      : btree_multiset_container(b, e, key_compare(), alloc) {}
+
+  // Initializer list constructors.
+  btree_multiset_container(std::initializer_list<init_type> init,
+                           const key_compare &comp = key_compare(),
+                           const allocator_type &alloc = allocator_type())
+      : btree_multiset_container(init.begin(), init.end(), comp, alloc) {}
+  btree_multiset_container(std::initializer_list<init_type> init,
+                           const allocator_type &alloc)
+      : btree_multiset_container(init.begin(), init.end(), alloc) {}
+
+  // Insertion routines.
+  iterator insert(const value_type &v) { return this->tree_.insert_multi(v); }
+  iterator insert(value_type &&v) {
+    return this->tree_.insert_multi(std::move(v));
+  }
+  iterator insert(const_iterator hint, const value_type &v) {
+    return this->tree_.insert_hint_multi(iterator(hint), v);
+  }
+  iterator insert(const_iterator hint, value_type &&v) {
+    return this->tree_.insert_hint_multi(iterator(hint), std::move(v));
+  }
+  template <typename InputIterator>
+  void insert(InputIterator b, InputIterator e) {
+    this->tree_.insert_iterator_multi(b, e);
+  }
+  void insert(std::initializer_list<init_type> init) {
+    this->tree_.insert_iterator_multi(init.begin(), init.end());
+  }
+  template <typename... Args>
+  iterator emplace(Args &&... args) {
+    // Use a node handle to manage a temp slot.
+    auto node = CommonAccess::Construct<node_type>(this->get_allocator(),
+                                                   std::forward<Args>(args)...);
+    return this->tree_.insert_multi(CommonAccess::GetSlot(node));
+  }
+  template <typename... Args>
+  iterator emplace_hint(const_iterator hint, Args &&... args) {
+    // Use a node handle to manage a temp slot.
+    auto node = CommonAccess::Construct<node_type>(this->get_allocator(),
+                                                   std::forward<Args>(args)...);
+    return this->tree_.insert_hint_multi(iterator(hint),
+                                         CommonAccess::GetSlot(node));
+  }
+  iterator insert(node_type &&node) {
+    if (!node) return this->end();
+    iterator res =
+        this->tree_.insert_multi(params_type::key(CommonAccess::GetSlot(node)),
+                                 CommonAccess::GetSlot(node));
+    CommonAccess::Destroy(&node);
+    return res;
+  }
+  iterator insert(const_iterator hint, node_type &&node) {
+    if (!node) return this->end();
+    iterator res = this->tree_.insert_hint_multi(
+        iterator(hint),
+        std::move(params_type::element(CommonAccess::GetSlot(node))));
+    CommonAccess::Destroy(&node);
+    return res;
+  }
+
+  // Node extraction routines.
+  template <typename K = key_type>
+  node_type extract(const key_arg<K> &key) {
+    const std::pair<iterator, bool> lower_and_equal =
+        this->tree_.lower_bound_equal(key);
+    return lower_and_equal.second ? extract(lower_and_equal.first)
+                                  : node_type();
+  }
+  using super_type::extract;
+
+  // Merge routines.
+  // Moves all elements from `src` into `this`.
+  template <
+      typename T,
+      typename absl::enable_if_t<
+          absl::conjunction<
+              std::is_same<value_type, typename T::value_type>,
+              std::is_same<allocator_type, typename T::allocator_type>,
+              std::is_same<typename params_type::is_map_container,
+                           typename T::params_type::is_map_container>>::value,
+          int> = 0>
+  void merge(btree_container<T> &src) {  // NOLINT
+    for (auto src_it = src.begin(), end = src.end(); src_it != end; ++src_it) {
+      insert(std::move(params_type::element(src_it.slot())));
+    }
+    src.clear();
+  }
+
+  template <
+      typename T,
+      typename absl::enable_if_t<
+          absl::conjunction<
+              std::is_same<value_type, typename T::value_type>,
+              std::is_same<allocator_type, typename T::allocator_type>,
+              std::is_same<typename params_type::is_map_container,
+                           typename T::params_type::is_map_container>>::value,
+          int> = 0>
+  void merge(btree_container<T> &&src) {
+    merge(src);
+  }
+};
+
+// A base class for btree_multimap.
+template <typename Tree>
+class btree_multimap_container : public btree_multiset_container<Tree> {
+  using super_type = btree_multiset_container<Tree>;
+  using params_type = typename Tree::params_type;
+  friend class BtreeNodePeer;
+
+ public:
+  using mapped_type = typename params_type::mapped_type;
+
+  // Inherit constructors.
+  using super_type::super_type;
+  btree_multimap_container() {}
+};
+
+}  // namespace container_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_CONTAINER_INTERNAL_BTREE_CONTAINER_H_
--- a/Show More
+++ b/Show More