Lee Revell wrote:
On Sat, 2005-08-20 at 11:38 -0700, Howard Chu wrote:
> But I also found that I needed to add a new yield(), to work around
> yet another unexpected issue on this system - we have a number of
> threads waiting on a condition variable, and the thread holding the
> mutex signals the var, unlocks the mutex, and then immediately
> relocks it. The expectation here is that upon unlocking the mutex,
> the calling thread would block while some waiting thread (that just
> got signaled) would get to run. In fact what happened is that the
> calling thread unlocked and relocked the mutex without allowing any
> of the waiting threads to run. In this case the only solution was
> to insert a yield() after the mutex_unlock().
That's exactly the behavior I would expect. Why would you expect
unlocking a mutex to cause a reschedule, if the calling thread still
has timeslice left?
That's beside the point. Folks are making an assertion that
sched_yield() is meaningless; this example demonstrates that there are
cases where sched_yield() is essential.
--
-- Howard Chu
Chief Architect, Symas Corp. http://www.symas.com
Director, Highland Sun http://highlandsun.com/hyc
OpenLDAP Core Team http://www.openldap.org/project/
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