Re: [boost] Probably bug in condition::timed_wait()

From: Alexander Terekhov (terekhov_at_[hidden])
Date: 2006-10-09 02:22:34

Peter Dimov wrote:
> 
> Alexander Terekhov wrote:
> > Peter Dimov wrote:
> >>
> >> Pavel Syomin wrote:
> >>
> >>> This is solve my problems, but why there is nothing about spurious
> >>> wakeup in boost documentation?...
> >>
> >> The older documentation
> >>
> >> http://web.archive.org/web/20041024220516/boost.org/libs/thread/doc/condition.html
> >>
> >> does have a few sentences that mention spurious wakeups; I've no
> >> idea how they got lost. I'll CC: the dev list.
> >
> > The docu might tell something not only about spurious wakeups but
> > also about the fact that return of timedout status doesn't preclude
> > consumption of a signal issued concurrently (note that thread
> > cancel delivery does preclude it).
> 
> Hey!
> 
> Does this mean that timed_wait( lock, xt, pred ) has a bug? Instead of
> 
> while (!pred()) { if (!timed_wait(lock, xt)) return false; } return true;
> 
> it needs to be
> 
> while (!pred()) { if (!timed_wait(lock, xt)) return pred(); } return true;
> 
> otherwise a 'false' return can consume a signal meant for someone else
> without notifying the caller to handle the pred() == true case?

Yup. 

Another possible fix is to broadcast() (signal() is not enough).

while (!pred()) { if (!timed_wait(lock, xt)) return broadcast(), false; }

Roland will like that. ;-)

regards,
alexander.