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Thread Safety Analysis (TSA) for C

TSA is a static analysis tool for clang.

By adding annotations (attributes) to the source code that is using the POSIX threads API, and compiling with

clang -Wthread-safety

The source code is analyzed in compile-time for unsafe locking patterns that would lead into data races or deadlocks, or both.

The official documentation for TSA is

https://clang.llvm.org/docs/ThreadSafetyAnalysis.html

While that page talks only about using TSA with C++, it is quite possible to use most of the functionality with plain C.

That is, in fact, why this repository exists.

Usage

  1. Include the tsa.h into your code where you use POSIX mutexes to coordinate POSIX threads' access to data.
  2. Use tsa_mutex instead of pthread_mutex_t.
  3. Annotate your code with the TSA macros to explain what you think should be the "mutex protocol" to access your critical resources.
  4. Compile with clang -Wthread-safety.
  5. Suffer.
  6. Enjoy.

You can see example usage and the errors caused by issuing

make

Each of the example programs demonstrates one particular type of error.

For example:

tsa_mutex mut;
int g TSA_GUARDED_BY(&mut);
int main {
  g = 1;  // This would be bad.
}

To see how to fix the problems, issue

make pass

and study the example programs.

The first branch of the #ifndef TSA_PASS shows the wrong way (which may be: "doing nothing"), while the second branch, the #else, shows the right way.

TSA is not TSAN

TSA is not the same thing as thread sanitizer or tsan.

The TSA is completely compile-time, whereas the thread sanitizer adds instrumentation to the compiler output so that the runtime can detect data races during execution. The added instrumentation adds some execution overhead, and quite considerable memory overhead. None of this happens with TSA.

clang only

As far as I know TSA is available only for clang, not gcc. It should be fully available since clang 3.6.

License

The tsa.h is distributed under the MIT license, which is compatible with the clang (LLVM) license: http://llvm.org/docs/DeveloperPolicy.html#license

The license is both inlined to tsa.h, and available as a separate file LICENSE, directly from https://opensource.org/licenses/MIT

Acknowledgments

I would not have delved into this without the Perl 5 project. One of the build modes of Perl 5 is to build with support for POSIX threads, and to sanity check the logic of that, I found out that clang had TSA. The Perl 5 Porters (the Perl 5 development and maintenance project) helped out in testing the TSA C API, special thanks to Craig Berry and Jerry Hedden. You will find something very much like tsa.h as a part of perl.h in the Perl 5 source code, courtesy of myself.

Author

Jarkko Hietaniemi <[email protected]>