Pthread_cond_wait if cancelled leaves mutex locked deadlocking other threads?!

[mynickmynick]

From the following source code

int pthread_cond_wait(pthread_cond_t *cond, pthread_mutex_t *mutex)
{
volatile pthread_descr self = thread_self();

__pthread_lock(&cond->__c_lock, self);
enqueue(&cond->__c_waiting, self);
__pthread_unlock(&cond->__c_lock);
pthread_mutex_unlock(mutex);
suspend_with_cancellation(self);
pthread_mutex_lock(mutex);
/* This is a cancellation point */
if (THREAD_GETMEM(self, p_canceled)
&& THREAD_GETMEM(self, p_cancelstate) == PTHREAD_CANCEL_ENABLE) {
/* Remove ourselves from the waiting queue if we're still on it */
__pthread_lock(&cond->__c_lock, self);
remove_from_queue(&cond->__c_waiting, self);
__pthread_unlock(&cond->__c_lock);
pthread_exit(PTHREAD_CANCELED);
}
return 0;
}

it seems that when a thread gets canceled while waiting for cond it performs
pthread_mutex_lock(mutex);
...
pthread_exit(PTHREAD_CANCELED);

and leaves mutex locked?!
so anothe thread is potentially deadlocked?!
I tried to look in the source for pthread_exit() if and when the mutex is released but I didn't figure out!


So may be to prevent this the correct usage is

  pthread_mutex_lock(mutex);
  pthread_cleanup_push(pthread_mutex_unlock,mutex);
  while (...) pthread_cond_wait(cond,mutex); 
......
  pthread_cleanup_pop();
  pthread_mutex_unlock(mutex);

what you think?

[brewbuck]

So may be to prevent this the correct usage is

  pthread_mutex_lock(mutex);
  pthread_cleanup_push(pthread_mutex_unlock,mutex);
  while (...) pthread_cond_wait(cond,mutex); 
......
  pthread_cleanup_pop();
  pthread_mutex_unlock(mutex);

what you think?

Almost right, except the call to pthread_cleanup_pop should look like:

pthread_cleanup_pop(0);
pthread_mutex_unlock(mutex);

Or, just allow the cleanup handler to run itself when you pop it, unlocking the mutex for you:

pthread_cleanup_pop(1);

[mynickmynick]

ok great
thank you very much