Subj : Real cause of spurius wakeups
To   : comp.programming.threads
From : Vladimir Prus
Date : Thu Mar 31 2005 06:43 pm


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. I'm specifically talking about
spurious wakeup caused by pthread implementation, not the one caused by
loose predicate checking on the notifying side, or "stolen wakeup". I
looked in archives for this group, and in the FAQ, but found only vague
statements that on some SMP systems avoiding spurious wakeup is too hard.

I understand that pthread_cond_wait need to be wrapped in a loop even if
spurious wakeups did not exist. I'm asking just because the wakeups are
mentioned everywhere, but I never seen a complete explanations.

Thanks in advance,
Volodya

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