It can understand Python variable assignments, SQL statements and Redis commands, which can detect races that cross abstraction boundaries, e.g. a deadlock between threading.Lock() in one thread and a SQL row lock in another.

To use it, do `pip install frontrun`[1] then put the following in a pytest case:

  result = frontrun.explore(
      setup=Counter,
      workers=Counter.increment,
      count=2,
  )
  result.assert_holds()

My hope is that this will allow authors of libraries which are not currently threadsafe to weather the freethreading transition more easily or to raise the bar for issue submissions involving race conditions. I've put a lot of work into making races deterministic and making the error trace interpretable, demonstrating why that sequence of events that triggers the race. I'd love any usability feedback or success/failure stories you have, and I'm happy to answer any questions about how it works.

[1] MacOS and Linux only.