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Re: pthread_* functionality currently in OS X

On Wednesday, March 27, 2002, at 03:03 PM, Conrad G T Yoder wrote:
At Wed, 27 Mar 2002 11:43:32 -0800, Matt Watson <email@hidden> wrote: 

On Wednesday, March 27, 2002, at 11:29  AM, Conrad G T Yoder wrote:

  if (pthread_cond_wait(&condVar, &mutexVar) != 0) {
    CantHappen();
  }


What's the condition? You must call pthread_cond_wait() within a loop,
with a predicate:

pthread_mutex_lock(&m);
while (condition == 0) {
	pthread_cond_wait(&c, &m);
}
/* Do some stuff */
pthread_mutex_unlock(&m);


All I am looking to do is have this thread sit and wait forever - no one
will be signalling it ever.  That's why there's no loop.

Not good enough. The pthread_cond_wait() call can (and does) return early. In particular, if the waiting thread is the target of a signal, pthread_cond_wait() returns. This is required behavior, because while running a signal handler the thread is not waiting on the condition and may miss a wakeup. So instead of that possibility, it returns to the caller and makes it determine whether "continued waiting" is the proper behavior or the condition was satisfied and it can return. You would just need a forever loop around your pthread_cond_wait() if you wanted it to wait forever.

--Jim
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References: 
 >Re: pthread_* functionality currently in OS X (From: Conrad G T Yoder <email@hidden>)



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