[PATCH] D18811: Fix a race condition in support library ThreadPool

[Jason Henline via llvm-commits]

jhen added a comment.

To elaborate on the race condition, TSAN warns about the following when running the AsyncBarrier unit test (irrelevant stack frames removed):

  WARNING: ThreadSanitizer: data race (pid=690669)
    Read of size 8 at 0x7fff3627b2b8 by main thread (mutexes: write M1928):
      wait<(lambda at lib/Support/ThreadPool.cpp:79:28)>
    Previous write of size 8 at 0x7fff3627b2b8 by thread T5 (mutexes: write M1849):
      operator() lib/Support/ThreadPool.cpp:53

So basically the wait routine can be checking whether the task queue is empty at the same time a thread can be trying to remove an element from the task queue. The queue data structure is not thread safe, so this is a race.

Sorry for the misleading description. I hope this clears up the issue.


http://reviews.llvm.org/D18811