If you unlock an already unlocked mutex, is the behavior undefined?

Question

If you unlock an already unlocked mutex, is the behavior unsafe, safe, or undefined?

The purpose of the question is related to the following code, where I don\'t kno

Answer 1

You don't need to do it that way. Try this:

    // This chunk of code makes dual locking semi-autonomous.
int c_lckd = 0, q_lckd = 0;
if (pthread_mutex_trylock(&crunch_mutex) == 0) c_lckd = 1;
if (pthread_mutex_trylock(&queue_mutex) == 0) q_lckd = 1;

if (c_lckd && q_lckd) {
  printf("cr = %d, max = %d, cnt = %d\n",
    crunching, max_crunching, queue_count(conn_queue));
  if (crunching < max_crunching && queue_count(conn_queue)) {
    pthread_t tid =
      pthread_create(
        &tid,
        NULL,
        crunch_conn,
        (void *)queue_dequeue(conn_queue)
      );
    crunching++;
  }

}

if (q_lckd) { QUEUE_UNLOCK; q_lckd = 0; }
if (c_lckd) { CRUNCH_UNLOCK; c_lckd = 0; }

It's a little easier to follow and doesn't risk trying to unlock an unlocked mutex.