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    SubjectRe: sched_yield() makes OpenLDAP slow
    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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