Relacy Race Detector

Meticulous synchronization algorithm verifier for relaxed memory models

• http://www.1024cores.net/home/relacy-race-detector
• http://www.1024cores.net/home/relacy-race-detector/rrd-introduction

Building - for contributors and maintainers of Relacy

To developer the Relacy library itself, use CMake to configure a build, selecting your compiler and C++ standard of choice.

mkdir build && cd build
cmake \
  -DCMAKE_CXX_STANDARD=20 \
  -DCMAKE_CXX_COMPILER=g++ \
  -DCMAKE_BUILD_TYPE=RelWithDebInfo \
  ..
make -j 8
ctest # Run tests

To test that all supported toolchains on your platform build and run correctly, use the top level Makefile as a helper to build N different configurations. For example, on a Linux host, the following will create one CMake build directory for GCC and Clang and for each C++ 11 through C++ 23. Then, it will run the unit tests on all build configurations. This should be done before submitting pull requests (at least until we can setup CI to run on pull requests).

make build-all -j 8
make test-all -j 8

Toolchains known to work

At a minimum, a C++11 compiler is assumed. The below compilers have been recently (Jan 2026) tested and confirmed to work

• Linux x86_64
  • GCC-11-14, C++11 - C++23 (where GCC supports the version)
  • Clang-18-21, C++11 - C++23 (where Clang supports the version)
• Mac x86_64 (Clang-15, 17), C++11 - C++23

Overriding std:: types

Relacy defines its own version of types like rl::atomic, rl::thread, etc, to allow writing Relacy tests in terms of the rl:: types. However, in some cases it can be convenient to test existing code that uses std:: names without rewriting the code to use rl:: types.

Relacy has support to intercept standard headers like <atomic> and alias the std types in the rl namespace. To do this, you must

• Add -Irelacy/fakestd to your include path
• Ensure "relacy/relacy_std.hpp" is the first include in your .cpp source file

Note: This approach may not work as compilers and standard library implementations evolve, and may require changes to Relacy for the fakestd implementation to keep working.