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Subject: RE: pthread_cond_wait does not relock mutex on release
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Date: Wed, 17 Apr 2002 17:21:37 +1000
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From: "Robert Collins" <robert DOT collins AT itdomain DOT com DOT au>
To: "Michael Labhard" <ince AT pacifier DOT com>, <cygwin AT cygwin DOT com>
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> -----Original Message-----
> From: Michael Labhard [mailto:ince AT pacifier DOT com] 
> Sent: Wednesday, April 17, 2002 5:01 AM
> To: cygwin AT cygwin DOT com
> Subject: pthread_cond_wait does not relock mutex on release
> 
> 
> Don't no if anyone else has noticed this:  the 
> pthread_cond_wait when signalled does not lock the associated 
> mutex again.  

This is incorrect. It does lock the mutex again.:

(from __pthread_cond_dowait which implemented pthread_cond_wait)

  (*themutex)->Lock ();
  if (last == true)
    (*cond)->mutex = NULL;
  if (pthread_mutex_lock (&(*cond)->cond_access))
    system_printf ("Failed to lock condition variable access mutex, this
%p", *c
ond);
  InterlockedDecrement (&((*themutex)->condwaits));
  if (pthread_mutex_unlock (&(*cond)->cond_access))
    system_printf ("Failed to unlock condition variable access mutex,
this %p",
*cond);

  return rv;
}

Chances are your test app is buggy, or you are making one or more
assumptions about the mutex type (ie recursiveness etc) that are
incorrect.

Rob

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