ThreadSanitizer

ThreadSanitizer, commonly abbreviated as TSan, is a dynamic data race detector for multithreaded native programs. It is part of the LLVM Sanitizers family and is widely used to identify concurrency errors in C, C++, and other languages that compile with LLVM-based toolchains.

TSan operates by instrumenting code at compile time to monitor memory accesses and synchronization operations. It maintains metadata about memory locations and the happens-before relationships between actions performed by different threads, typically using shadow memory and vector clocks. When two or more threads access the same memory location concurrently, and at least one access is a write without proper synchronization, TSan reports a data race. Reports include the location in source code, stack traces, participating threads, and the nature of the conflicting access.

Usage and availability: To use it, compile with -fsanitize=thread (and -g for debugging information). Run the program normally; a detected race is reported on standard error with a stack trace. TSan is supported with the Clang/LLVM toolchain on major platforms such as Linux and macOS, and is available in compatible toolchains on Windows. It can detect races in C and C++, and in other languages that can be built with LLVM-based compilers, including Rust in typical LLVM workflows.

Limitations: The instrumentation introduces substantial runtime overhead and memory usage, which can slow execution and alter timing in multithreaded programs. It may not report races in code that runs in non-instrumented libraries or in certain intricate synchronization patterns, and false positives or negatives can occur in edge cases.