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Date: Wed, 3 May 2006 09:06:43 -0700
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Organization: PHP
Subject: Re: Shared hashtable
From: pollita@php.net ("Sara Golemon")

> I'm being asked about the possibility of creating an extension that will 
> cache some data from a MySQL DB in-memory. I've been reading various 
> online resources regarding building extensions and cannot find an answer 
> to the following question... Is there a way to create a hashtable in the 
> extension which will be available to all of the Apache children without 
> resorting to shared memory?
>
You want to *share* something in *memory* between two processes.  Yep, ya 
pretty much need shared memory...

> It's important that only one instance of the data exists for two 
> reasons... 1) It's a fairly large amount of data and 2) it will change as 
> the application runs. I've created a small test extension using 
> MODULE_GLOBALS the results of which suggest that these variables are per 
> process. I'm just looking for some confirmation that shared memory is the 
> way to go before I jump down that particular black hole.
>
Yes, Module Globals are per-process (or per-thread if your under a threaded 
sapi).  In either case, these are specifically designed to *prevent* 
concurrent requests from accessing the same data.

-Sara

> TIA.
>
> -Stut