RE: pthread_mutex_unlock (was Re: sched_yield() makes OpenLDAP slow)

[David Schwartz]

> > 	So you cannot write an application that can tell the difference.

> Not true.  The code for the relinquishing thread could indeed
> tell the difference.
>
> -ml

	It can tell the difference between the other thread getting the mutex first
and it getting the mutex first. But it cannot tell the difference between an
implementation that puts random sleeps before calls to 'pthread_mutex_lock'
and an implementation that has the allegedly non-compliant behavior. That
makes the behavior compliant under the 'as-if' rule.

	If you don't believe me, try to write a program that prints 'non-compliant'
on a system that has the alleged non-compliance but is guaranteed not to do
so on any compliant system. It cannot be done.

	In order to claim the alleged compliance, you would have to know that a
thread waiting for a mutex did not get it. But there is no possible way you
can know that another thread is waiting for the mutex (as opposed to being
about to wait for it). So you can never detect the claimed non-compliance,
so it's not non-compliance.

	This is definitive, really. It 100% refutes the claim.

	DS


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