[cfe-dev] libc++ mutex destructor assertion

[Zachary Turner]

Currently recursive_mutex::~recursive_mutex() asserts if
pthread_mutex_destroy fails, and one of the reasons this can fail is if the
mutex is locked by another thread.  This leads to the assert being
triggered in the following sample program:

#include <mutex>
#include <stdlib.h>
#include <stdio.h>

std::recursive_mutex& getMutex() {
  static std::recursive_mutex mutex;
  return mutex;
}

void* ThreadFunc(void* arg) {
  std::lock_guard<std::recursive_mutex> Lock(getMutex());
  exit(1);
  return nullptr;
}


int main(int argc, char** argv) {
  pthread_t thread;
  pthread_attr_t attr;

  pthread_attr_init(&attr);
  pthread_create(&thread, &attr, ThreadFunc, nullptr);
  pthread_join(thread, nullptr);

  return 0;
}


Is this assertion bogus?  I'm trying to replace a mutex in LLVM with
recursive_mutex but am blocked by this because the builder on FreeBSD
actually aborts here due to the assertion.

What's the best way to go about resolving this?  Even if we decide that the
assertion should be removed, it's not going to stop the builders from
failing every time until they get a new build of libc++, and I don't think
(but maybe I'm wrong?) the builders build libc++, but rather just use the
one that's already installed.

Thoughts?
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