Messages in this thread | | | Date | Sat, 14 Jan 2006 11:29:33 -0800 | From | Howard Chu <> | Subject | Re: sched_yield() makes OpenLDAP slow |
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Resurrecting a dead horse... > *From: *Lee Revell > *Date: * Sat Aug 20 2005 - 15:57:36 EST > > ------------------------------------------------------------------------ > 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? > > Lee
POSIX requires a reschedule to occur, as noted here: http://blog.firetree.net/2005/06/22/thread-yield-after-mutex-unlock/
The relevant SUSv3 text is here http://www.opengroup.org/onlinepubs/000095399/functions/pthread_mutex_unlock.html
I suppose if pthread_mutex_unlock() actually behaved correctly we could remove the other sched_yield() hacks that didn't belong there in the first place and go on our merry way.
-- -- 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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