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From: Paul Brook <paul@codesourcery.com>
Subject: Re: [Qemu-devel] [patch 1/2] qemu: sem/thread helpers
Date: Tue, 17 Mar 2009 23:07:07 +0000
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To: qemu-devel@nongnu.org
Cc: Anthony Liguori <aliguori@us.ibm.com>, Marcelo Tosatti <mtosatti@redhat.com>

On Tuesday 17 March 2009, Marcelo Tosatti wrote:
> On Sun, Mar 15, 2009 at 04:15:52PM +0200, Avi Kivity wrote:
> > Marcelo Tosatti wrote:
> >> +
> >> +struct QemuSem {
> >> +    sem_t sema;
> >> +};
> >
> > Why aren't you using pthread_mutex_t?
>
> Because we want the thread waiting on the lock to be awakened
> once the holder releases it. This does not happen with pthread
> mutexes AFAIK.

Really? I'd be surprised if there's any difference. The whole point of a mutex 
is that it blocks until the other thread releases it.  At best it sounds like 
you're making fairly sketchy assumptions about the host OS scheduler 
heuristics.

Paul