Abseil - C++ Common Libraries

Cygwin Port (cygwin/support branch)

This branch adds Cygwin support to Abseil LTS 20250512.1.

Abseil does not officially support Cygwin. An upstream effort is underway (abseil/abseil-cpp#2012, Carlo Bramini) but has not yet been merged. This branch carries 10 minimal patches -- 5 derived from that PR, 5 discovered during testing -- that bring the full test suite to 218/218 passing.

The patches exist to support a Cygwin build of Protocol Buffers v34.1, which depends on this version of Abseil. They are intended as a stopgap until Cygwin support lands upstream.

The end goal is grpcio (Python gRPC bindings) on Cygwin. The dependency chain is:

psutil <- pypinfo <- grpcio <- protobuf <- abseil-cpp

Building on Cygwin

Prerequisites: GCC 13+, CMake 3.16+, Cygwin x86_64.

GoogleTest must be available for the test suite. Either let CMake download it (ABSL_USE_GOOGLETEST_HEAD=ON) or point to an installed copy (ABSL_USE_EXTERNAL_GOOGLETEST=ON). The second option is required if you plan to cmake --install and have downstream projects consume the result via find_package(absl) -- see Install note below.

Option A -- download GoogleTest at configure time:

mkdir build && cd build
cmake /path/to/abseil-cpp \
  -DCMAKE_CXX_STANDARD=17 \
  -DCMAKE_BUILD_TYPE=Release \
  -DCMAKE_CXX_FLAGS="-D_GLIBCXX_USE_CXX11_ABI=1 -DGTEST_HAS_PTHREAD=1" \
  -DABSL_BUILD_TESTING=ON \
  -DABSL_USE_GOOGLETEST_HEAD=ON
cmake --build . --parallel 8
ctest --timeout 300

Option B -- use installed GoogleTest (required for install/release):

mkdir build && cd build
cmake /path/to/abseil-cpp \
  -DCMAKE_CXX_STANDARD=17 \
  -DCMAKE_BUILD_TYPE=Release \
  -DCMAKE_PREFIX_PATH=/usr/local \
  -DCMAKE_CXX_FLAGS="-D_GLIBCXX_USE_CXX11_ABI=1 -DGTEST_HAS_PTHREAD=1" \
  -DABSL_BUILD_TESTING=ON \
  -DABSL_USE_EXTERNAL_GOOGLETEST=ON \
  -DABSL_FIND_GOOGLETEST=ON
cmake --build . --parallel 8
ctest --timeout 300

Both -D flags in CMAKE_CXX_FLAGS are required:

• _GLIBCXX_USE_CXX11_ABI=1 -- Cygwin's libstdc++ defaults to the old COW string ABI (sizeof(std::string) = 8). Protobuf requires the SSO ABI (sizeof(std::string) = 32). Both Abseil and Protobuf must agree.

• GTEST_HAS_PTHREAD=1 -- googletest's header auto-detection omits Cygwin from its pthread platform list. Without this flag, libgmock.a and test binaries disagree on the Mutex class layout, causing any gmock-based test to crash. Only needed when building tests.

Binary release

Pre-built static libraries for Cygwin x86_64 (GCC 13.4.0, Release mode) are available on the Releases page, tagged for use with Protobuf 7.35.0.

GoogleTest 1.16.0 is vendored inside the tarball under lib/absl/vendor/. Abseil's cmake config references GTest::gtest and GTest::gmock for test helper targets that protobuf's test suite requires; the vendored copy satisfies these references automatically without conflicting with any system-wide GoogleTest installation.

The tarball installs to /usr/local, which avoids conflicting with any system abseil installed by the Cygwin package manager in /usr.

# Install
cd / && tar xzf abseil-cpp-20250512.1-cygwin-x86_64.tar.gz

This places:

• Libraries in /usr/local/lib/libabsl_*.a
• Headers in /usr/local/include/absl/
• CMake config in /usr/local/lib/cmake/absl/
• Vendored GoogleTest in /usr/local/lib/absl/vendor/
• pkg-config in /usr/local/lib/pkgconfig/absl_*.pc

To use from CMake:

list(APPEND CMAKE_PREFIX_PATH /usr/local)
find_package(absl REQUIRED)

No separate find_package(GTest) is needed -- abslConfig.cmake finds the vendored copy automatically. If your project already loads GTest before finding abseil, the vendored copy is skipped.

Building with a custom prefix

To install to a location other than /usr/local, add -DCMAKE_INSTALL_PREFIX to the cmake configure step and install after building:

mkdir build && cd build
cmake /path/to/abseil-cpp \
  -DCMAKE_CXX_STANDARD=17 \
  -DCMAKE_BUILD_TYPE=Release \
  -DCMAKE_INSTALL_PREFIX=/path/to/prefix \
  -DCMAKE_PREFIX_PATH=/path/to/prefix \
  -DCMAKE_CXX_FLAGS="-D_GLIBCXX_USE_CXX11_ABI=1 -DGTEST_HAS_PTHREAD=1" \
  -DABSL_BUILD_TESTING=ON \
  -DABSL_USE_EXTERNAL_GOOGLETEST=ON \
  -DABSL_FIND_GOOGLETEST=ON
cmake --build . --parallel 8
ctest --timeout 300
cmake --install .

GoogleTest must be installed at the prefix before building abseil. CMAKE_PREFIX_PATH tells cmake where to find it.

The cmake config files are relocatable -- they compute the prefix from their own install path, so find_package(absl) works regardless of where the tree is rooted, as long as the prefix is in CMAKE_PREFIX_PATH:

list(APPEND CMAKE_PREFIX_PATH /path/to/prefix)
find_package(absl REQUIRED)

Downstream: Protobuf Cygwin port

The matching Protobuf build is at phdye-cygwin/protobuf (branch cygwin/update-port), targeting Protobuf 7.35.0. Protobuf's CMake build fetches Abseil 20250512.1 from GitHub; the patches here must be applied to the fetched source after cmake configure and before cmake --build.

Known limitations

• Build time: ~19 minutes on an 8-core machine with -j8.
• Test timeouts: ctest --timeout 300 is needed for two tests that are slow by design, not due to Cygwin:
  • flags_sequence_lock_test (~225s) -- 115 parameterized cases each running a concurrent read/write loop with a hardcoded 5-second deadline.
  • mutex_test (~103s) -- 72 timeout-verification cases with deliberate sub-second sleeps (450ms, 900ms). These would exceed a 60-second timeout on any platform.

Upstream tracking

When abseil/abseil-cpp#2012 merges, 5 of the 10 patches here become redundant (the 5 derived from that PR). The remaining patches address issues not covered by PR #2012:

Patch	Why it's separate
config.h (ABSL_HAVE_MMAP)	PR #2012 omits this; build fails without it
log/internal/config.h (Tid width)	Thread ID truncation in log output
base/internal/raw_logging.cc (POSIX write)	Raw log output silently discarded
strings/charconv_test.cc (NaN)	Test-only: Cygwin strtod() platform difference
log/stripping_test.cc (/proc/self/exe)	Test-only: Cygwin provides this like Linux

Patch summary

File	Purpose
policy_checks.h	Remove #error "Cygwin is not supported"
attributes.h	Disable weak symbols (PE/COFF)
config.h	Recognize Cygwin mmap support
low_level_alloc.h	Correct allocation capability flags
sysinfo.cc	Fix GetTID cast for pointer-sized pthread_t
sysinfo.h	Widen pid_t to hold thread handle
log/internal/config.h	Widen Tid to prevent thread ID truncation in logs
base/internal/raw_logging.cc	Enable POSIX write() for raw log output
strings/charconv_test.cc	Accommodate Cygwin strtod() NaN behavior
log/stripping_test.cc	Enable /proc/self/exe path

---

The repository contains the Abseil C++ library code. Abseil is an open-source collection of C++ code (compliant to C++17) designed to augment the C++ standard library.

Table of Contents

• Cygwin Port
• About Abseil
• Quickstart
• Building Abseil
• Support
• Codemap
• Releases
• License
• Links

About Abseil

Abseil is an open-source collection of C++ library code designed to augment the C++ standard library. The Abseil library code is collected from Google's own C++ code base, has been extensively tested and used in production, and is the same code we depend on in our daily coding lives.

In some cases, Abseil provides pieces missing from the C++ standard; in others, Abseil provides alternatives to the standard for special needs we've found through usage in the Google code base. We denote those cases clearly within the library code we provide you.

Abseil is not meant to be a competitor to the standard library; we've just found that many of these utilities serve a purpose within our code base, and we now want to provide those resources to the C++ community as a whole.

Quickstart

If you want to just get started, make sure you at least run through the Abseil Quickstart. The Quickstart contains information about setting up your development environment, downloading the Abseil code, running tests, and getting a simple binary working.

Building Abseil

Bazel and CMake are the official build systems for Abseil. See the quickstart for more information on building Abseil using the Bazel build system. If you require CMake support, please check the CMake build instructions and CMake Quickstart.

Support

Abseil follows Google's Foundational C++ Support Policy. See this table for a list of currently supported versions compilers, platforms, and build tools.

Codemap

Abseil contains the following C++ library components:

• base
  The base library contains initialization code and other code which all other Abseil code depends on. Code within base may not depend on any other code (other than the C++ standard library).
• algorithm
  The algorithm library contains additions to the C++ <algorithm> library and container-based versions of such algorithms.
• cleanup
  The cleanup library contains the control-flow-construct-like type absl::Cleanup which is used for executing a callback on scope exit.
• container
  The container library contains additional STL-style containers, including Abseil's unordered "Swiss table" containers.
• crc The crc library contains code for computing error-detecting cyclic redundancy checks on data.
• debugging
  The debugging library contains code useful for enabling leak checks, and stacktrace and symbolization utilities.
• flags
  The flags library contains code for handling command line flags for libraries and binaries built with Abseil.
• hash
  The hash library contains the hashing framework and default hash functor implementations for hashable types in Abseil.
• log
  The log library contains LOG and CHECK macros and facilities for writing logged messages out to disk, stderr, or user-extensible destinations.
• memory
  The memory library contains memory management facilities that augment C++'s <memory> library.
• meta
  The meta library contains type checks similar to those available in the C++ <type_traits> library.
• numeric
  The numeric library contains 128-bit integer types as well as implementations of C++20's bitwise math functions.
• profiling
  The profiling library contains utility code for profiling C++ entities. It is currently a private dependency of other Abseil libraries.
• random
  The random library contains functions for generating pseudorandom values.
• status
  The status library contains abstractions for error handling, specifically absl::Status and absl::StatusOr<T>.
• strings
  The strings library contains a variety of strings routines and utilities.
• synchronization
  The synchronization library contains concurrency primitives (Abseil's absl::Mutex class, an alternative to std::mutex) and a variety of synchronization abstractions.
• time
  The time library contains abstractions for computing with absolute points in time, durations of time, and formatting and parsing time within time zones.
• types
  The types library contains non-container utility types.
• utility
  The utility library contains utility and helper code.

Releases

Abseil recommends users "live-at-head" (update to the latest commit from the master branch as often as possible). However, we realize this philosophy doesn't work for every project, so we also provide Long Term Support Releases to which we backport fixes for severe bugs. See our release management document for more details.

License

The Abseil C++ library is licensed under the terms of the Apache license. See LICENSE for more information.

Links

For more information about Abseil:

• Consult our Abseil Introduction
• Read Why Adopt Abseil to understand our design philosophy.
• Peruse our Abseil Compatibility Guarantees to understand both what we promise to you, and what we expect of you in return.