From owner-freebsd-threads@FreeBSD.ORG  Wed Jan 28 09:01:39 2004
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Date: Wed, 28 Jan 2004 12:01:27 -0500 (EST)
From: Daniel Eischen <eischen@vigrid.com>
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To: Mike Makonnen <mtm@identd.net>
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cc: Peter Kostouros <kpeter@melbpc.org.au>
Subject: Re: pthread_mutex_trylock() should never block
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On Wed, 28 Jan 2004, Mike Makonnen wrote:

> On Sun, Dec 07, 2003 at 01:34:31AM -0500, Daniel Eischen wrote:
> > 
> > The man page may not mention it, and that may be a bug, but I
> > think a pthread_mutex_trylock() on a non-recursive mutex is allowed
> > to return EDEADLK.
> > 
> >   http://www.opengroup.org/onlinepubs/007904975/functions/pthread_mutex_trylock.html
> > 
> >   If the mutex type is PTHREAD_MUTEX_ERRORCHECK, then error
> >   checking shall be provided. If a thread attempts to relock a
> >   mutex that it has already locked, an error shall be returned.
> >   If a thread attempts to unlock a mutex that it has not locked
> >   or a mutex which is unlocked, an error shall be returned.
> > 
> >   ...
> 
> If you look further down in the spec you will see:
> 
>    The pthread_mutex_trylock() function shall be equivalent to
>    pthread_mutex_lock(), except that if the mutex object referenced
>    by mutex is currently locked (by any thread, including
>    the current thread), the call shall return immediately...

Yes, but the implementation has to use internal locks to
keep the mutex in a consistent state.  There is no problem
here.

-- 
Dan Eischen