Subj : Re: Real cause of spurius wakeups
To   : comp.programming.threads
From : Alexander Terekhov
Date : Thu Mar 31 2005 07:19 pm


Vladimir Prus wrote:
> 
> Hello,
> 
> can somebody explain the real reason why spurious wakeups are possible. That
> is, why call to pthread_cond_wait can return without
> pthread_cond_broadcast/pthread_cond_signal. 

Because apart from realtime scheduling, 
pthread_cond_broadcast/pthread_cond_signal can be implemented as nop.

No kidding. 

  cond_wait: mutex::release_guard guard(mutex); sleep(random());

  cond_signal: nop

  cond_broadcast: nop


See also

http://terekhov.de/DESIGN-futex-CV.cpp
http://terekhov.de/DESIGN-futex-CV-with-async.cancelable-wait.txt

regards,
alexander.

.