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From Jeff Trawick <traw...@attglobal.net>
Subject Re: [PATCH] Allow pthread_mutex_t to be a cross-process lock
Date Mon, 02 Jul 2001 16:07:59 GMT
Justin Erenkrantz <jerenkrantz@ebuilt.com> writes:

> On Mon, Jul 02, 2001 at 08:21:10AM -0400, Jeff Trawick wrote:
> > Please don't commit just yet.
> 
> Should I back this out?  Ryan wants to T&R at 10AM PST.  I guess the
> easy "fix" would be to place fcntl() decision AFTER the 
> pthread_mutex_t support.

Definitely... HP-UX and OS/390 are now broken.  The shared memory
mechanism used by the cross-process pthread mutex support doesn't work
on those systems.

> > That piece of code decides not what kind of interprocess lock
> > mechanism APR *has* support for on the platform but what kind of
> > interprocess lock mechanism APR will *use* by default.
> 
> Correct, I knew that.  But, as seen by the other warning that was 
> triggered by this, no one actually has ever tested/maintained this code.
> Now, we can start to exercise it.  =-)  (Which is partly the reason why
> I was complaining about the 2.0.20 T&R taking in these changes...)

I'd say that the Apache AcceptMutex directive gives you plenty of
ability to exercise it without changing the default lock choice :)

> > I suspect that you misunderstood what that code is doing... otherwise,
> > you'd try to explain why you want to change the [usual] default
> > mechanism from fcntl() to interprocess pthread mutex.
> 
> Typically, from my understanding of things, pthread mutex should be 
> the option that lets us scale the best on the high-end.  From what 
> Bill said, this is what IBM ships with IBM HTTPD.  And, on Solaris, 
> you want to use pthread-related locking for best performance.  Now, I 
> could be wrong about this being the "best choice."

Basically, I think we changed the Apache default without a crisp
understanding of why it should change.  My understanding of things is
that on Solaris and AIX the best lock choice depends on the config of
Apache and the machine.  I can't tell you that fcntl is "better
overall" (whatever that means), but I don't see any info to support
the claim that pthread mutex is "better overall" either.

> What platforms are going to have pthread_mutex_t with SHARED_PROCESS
> that WORKS and not have this?

OS/390, HP-UX, dunno what else (if any)

-- 
Jeff Trawick | trawick@attglobal.net | PGP public key at web site:
       http://www.geocities.com/SiliconValley/Park/9289/
             Born in Roswell... married an alien...

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