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From: Alexander Terekhov (terekhov_at_[hidden])
Date: 2006-10-09 14:25:43

Peter Dimov wrote:
> > Another possible fix is to broadcast() (signal() is not enough).
> >
> > while (!pred()) { if (!timed_wait(lock, xt)) return broadcast(),
> > false; }
> Ummmm.... why is signal() not enough?

Threads A and B waiting (A does timed wait), C changes something,
signals and enters wait expecting another state change followed by
signaling from either A or B (whichever gets the signal and makes
processing). If A times out and only re-signal, that signal can be
consumed by C as spurious wake. So broadcast() is needed to wake B
and let it do the job.


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