Messages in this thread |  | | | Date | Sat, 20 Aug 2005 14:24:57 -0700 | | From | Howard Chu <> | | Subject | Re: sched_yield() makes OpenLDAP slow |
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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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