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From Aaron Bannert <aa...@ebuilt.com>
Subject Re: [PATCH] apr_lock.h update to remove/fix CROSS_PROCESS vs LOCKALL
Date Tue, 03 Jul 2001 16:25:26 GMT
On Tue, Jul 03, 2001 at 07:55:50AM -0700, Justin Erenkrantz wrote:
> Wouldn't it be better to try and determine which platforms/lock types 
> we don't need the APR_PROCESS_PRIVATE lock on when they attempt to 
> acquire APR_PROCESS_SHARED?  Is there some way to detect that?

That is what CROSS_PROCESS was for, but I argue that it is inappropriate
under other conditions (like threaded APR and threaded app).

> And, I believe we were saying that at least when you have threads, 
> that the current behavior of CROSS_PROCESS is unacceptable (as it 
> leaves the behavior on your process undefined which is completely 
> bogus).  So, for threaded APR, this is MUCH better, IMHO.
> 
> For PROCESS_SHARED, I guess a compromise would be to do:
> 
> create sharable mutex
> #if APR_HAS_THREADS
> if (sharable-mutex-type->flags & APR_SHARED_LOCK_DOES_NOT_LOCK_PRIVATE)
>     create per-process mutex
> #endif

That would be useful if APR_HAS_THREADS was somehow set per the app's
definition, not at APR's buildtime. I assume you're talking about this:

    case APR_PROCESS_SHARED:
        if (new->inter_meth->flags & APR_PROCESS_LOCK_MECH_IS_GLOBAL) {
            new->meth = new->inter_meth;  /* impl. uses one lock */
        }
        else {
            new->meth = &lockall_methods; /* impl. uses two locks */
        }
        break;


> I dunno.  We know if we don't have threads that the PRIVATE mutex is not
> important.  And, if our SHARED mutex also has the force of PRIVATE, then
> we don't even need to create the extra PRIVATE mutex.  Or, maybe just 
> always create the PRIVATE mutex if APR_HAS_THREADS is 1 (if we don't
> know if SHARED implies PRIVATE - which is our problem to begin with).
> 
> This could give the non-threaded users of APR even more reason to 
> specify "--without-threads" when configuring - which they should be 
> doing in the first place.

yes. And we want recompiles of APR, no?

> (Man, I can't stand those god-awful CROSS_PROCESS names.)  -- justin

(That's why I went for PROCESS_SHARED vs PROCESS_PRIVATE. "cross", "intra",
"inter", "blah" was used back and forth and was very confusing, especially
when "cross" isn't always truely "cross" since it's really just within
your process group, yadda yadda... :)

-aaron


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