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Date: Fri, 24 Apr 2015 18:47:45 +0300 (MSK)
From: Alexander Monakov <>
Subject: Re: Resuming work on new semaphore

One more thought.  In the original proposal, val[1] was a "wake count".  By
now we have drifted away a bit from that concept, with val[1] being used not
only in post/timedwait, but also in trywait/getvalue, trywait explicitely
performing post-stealing, and getvalue accounting for that.

So how about we try to stick with the original vision, and say that val[1] is
strictly for waiters leaving futex wait via non-error path?  The kernel tells
the poster via the return value of futex_wake whether the wake has caused any
waiter to resume execution.  The kernel already knows if any waiter was there
to accept a wake, and lets us know.  Can we somehow use that to implement
non-stealing wakeups?


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