Re: sched_yield() makes OpenLDAP slow

[Nikita Danilov <nikita@clusterfs.com>]

Helge Hafting writes:

[...]

 > 
 > >nothing says that it can't call pthread_mutex_lock and re-acquire the mutex
 > >before any other thread gets around to getting it.
 > >  
 > >
 > Wrong.
 > The spec says that the mutex must be given to a waiter (if any) at the
 > moment of release.  The waiter don't have to be scheduled at that
 > point, it may keep sleeping with its freshly unlocked mutex.  So the
 > unlocking thread may continue - but if it tries to reaquire the mutex
 > it will find the mutex taken and go to sleep at that point. Then other

You just described a convoy formation: a phenomenon that all reasonable
mutex implementation try to avoid at all costs. If that's what standard
prescribes---the standard has to be amended.

 > 
 > Helge Hafting

Nikita.
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