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From Nick Kew <...@apache.org>
Subject Re: Module External Configuration
Date Mon, 20 Jun 2011 22:20:02 GMT
On Mon, 20 Jun 2011 16:10:12 -0400
Mike Meyer <mwm@mired.org> wrote:


>   I assume that this is because a new process was spawned to
> > handle a new request and the updated memory didn't get carried over (even
> > though the pointer address didn't change...)

A new process may be spawned from time to time (though not directly
to handle a new request unless you have a very non-standard MPM).
You could check config data in a child_init hook.

However, if you have this problem, it's probably not your only one.
The data reverting suggests that your module's config may be held
on the server/config pool.  If that's being updated (and if the
updates involve any allocation at all) it's a memory leak.  Your
module should create its own config pool at child_init.  Then it
can read its own config data immediately, and - crucially -
whenever it re-reads the data it can first clean that pool to
reclaim memory.

> Put the configuration data into shared memory. Create and load the
> shared memory in the post config hook. Map the shared memory and
> potentially reload it during the child init hook. You'll need to use
> appropriate locking if you decide to reload it. Details on the locking
> will depend on the data structure details.

If you use shared memory, note that 2.3/2.4 have much better support for
it than earlier versions, with mod_socache and mod_slotmem.

However, this may not be the best thing to do.  You need to weigh up the
cost of maintaining a per-process copy of the config data against that
of using shared memory.  Both are valid solutions.

Also, do you want the overhead of a stat() every request to see if
anything has changed, or could it work on a time basis, so it only
performs a stat() if a certain time has elapsed since the last time?

-- 
Nick Kew

Available for work, contract or permanent.
http://www.webthing.com/~nick/cv.html

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