RE: pthread_cond_wait with multiple mutex variables

["Bharath Ramesh" <bramesh at vt dot edu>]

> -----Original Message-----
> From: Jonathan Nieder [mailto:jrnieder@gmail.com]
> 
> Hi Bhareth,
> 
> Bharath Ramesh wrote:
> 
> > I am using a benchmark which is associating multiple mutex variables
> with a
> > single condition variable
> [...]
> >  "The effect of using more than one mutex for concurrent
> > pthread_cond_timedwait() or pthread_cond_wait() operations on the
> same
> > condition variable is undefined;
> [...]
> > I am wondering if the behavior of the benchmark is correct.
> 
> I would have guessed that any behavior is correct, since the standard
> leaves the behavior undefined.  What am I missing?

What is confusing to me is that in the man page it states that "condition
variable becomes bound to a unique mutex when a thread waits on a the
condition variable". If I have more than one thread waiting of the condition
variable how does this binding between the condition variable and mutex
happen. Normally, when one uses condition variable signaling the code would
like something like

pthread_mutex_lock (&mutex);
...
...
...
...
pthread_cond_wait (&cond, &mutex);
...
...
...
...
pthread_mutex_unlock (&mutex);

Now if there is a unique one-to-one binding happening between the condition
variable and mutex variable then if the behavior is undefined there can be
incorrect data races because when the condition wait returns I need not be
holding the mutex lock.

Regards,

Bharath

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