Strange testsuite/thread/pthread1.cc

["H . J . Lu" <hjl at lucon dot org>]

In testsuite/thread/pthread1.cc, there are

  pthread_mutex_t fooLock;
  // This code uses a special case that allows us to use just one
  // condition variable - in general, don't use this idiom unless you
  // know what you are doing. ;-)
  pthread_cond_t fooCond;
};

void*
produce (void* t)
{
  task_queue& tq = *(static_cast<task_queue*> (t));
  int num = 0;
  while (num < iters)
    {
      pthread_mutex_lock (&tq.fooLock);
      while (tq.foo.size () >= max_size)
        pthread_cond_wait (&tq.fooCond, &tq.fooLock);
      tq.foo.push_back (num++);
      pthread_cond_signal (&tq.fooCond);
      pthread_mutex_unlock (&tq.fooLock);
    }
  return 0;
}

void*
consume (void* t)
{
  task_queue& tq = *(static_cast<task_queue*> (t));
  int num = 0;
  while (num < iters)
    {
      pthread_mutex_lock (&tq.fooLock);
      while (tq.foo.size () == 0)
        pthread_cond_wait (&tq.fooCond, &tq.fooLock);
      if (tq.foo.front () != num++)
        abort ();
      tq.foo.pop_front ();
      pthread_cond_signal (&tq.fooCond);
      pthread_mutex_unlock (&tq.fooLock);
    }
  return 0;
}

I don't see how it can work. You have no control which thread will run
at any given time. As the result, produce/consume may send singal to 
itself, which leads to dead lock. It happens on Linux/mips. May I ask
why only one condition variable is used?


H.J.