he condition variable
<I>cond</I> to be signalled. The thread execution is suspended and
does not consume any CPU time until the condition variable is
signalled. The <I>mutex</I> must be locked by the calling thread on
entrance to <B>pthread_cond_wait</B>. Before returning to the calling
thread, <B>pthread_cond_wait</B> re-acquires <I>mutex</I> (as per
<B>pthread_lock_mutex</B>). 
</P>
<P>Unlocking the mutex and suspending on the condition variable is
done atomically. Thus, if all threads always acquire the