Subj : Re: Real cause of spurius wakeups
To   : comp.programming.threads
From : Alexander Terekhov
Date : Fri Apr 01 2005 10:40 am


Vladimir Prus wrote:
[...]
> > http://terekhov.de/DESIGN-futex-CV.cpp
> > http://terekhov.de/DESIGN-futex-CV-with-async.cancelable-wait.txt
> 
> And how spurious wakeups are possible in that implementation? Unfortunately
> I can't immediately see that from 10K of code.

See .txt above. cond_broadcast() in cond_wait_cleanup_handler2() and
"FUTEX WAKE (cv->futex, ALL)" in cond_wait_cleanup() will cause
spurious wakeups (same effect due to futex token changes and races
with respect to futex wait and futex wake aside for a moment).

regards,
alexander.

.