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From Mark Wolgemuth <m...@employease.com>
Subject Re: Sample code for IPC in modules
Date Wed, 05 May 2004 15:13:55 GMT
(see note on hup cleanup below)
On May 5, 2004, at 2:51 AM, Sander Temme wrote:

> Hi Mark,
>
> Thanks for your observations.
>
> On May 4, 2004, at 7:18 PM, mark wrote:
>
>> 2)
>> Dettach is never needed. However, depending on desired results, it is 
>> usually desireable to perform a destroy when a HUP signal is sent, so 
>> that it gets created fresh by post_config
>>
>> I've run into the strange errors under high load where newly forked 
>> children startup thinking they are attached to the inherited shm seg, 
>> but are in fact attached to some anonymous new segment. No error is 
>> produced, but obviously it's a catastrophic situation.
>
> Yeah, that would be Bad. However, how does one hook into the SIGHUP 
> handler? AFAIK, httpd has its own signal handlers that do stuff like 
> restarts and graceful, and if I registered another handler, I would 
> overrule the one that httpd sets. Or is there a provision for a chain 
> of signal handlers?
>

You don't really need to worry about the SIGHUP handler, just tie a 
cleanup function to the pool used to create
it in post_config. This will be the process pool of the parent, and its 
cleanups get run after all the children exit on a restart. It works for 
me.

static apr_status_t
shm_cleanup_wrapper(void *unused) {
	int rv;
	if (shm_seg)
		rv = apr_shm_destroy(shm_seg);
	else
		rv = APR_EGENERAL;
	return rv;
}

then in post_config:

apr_pool_cleanup_register(pool, NULL, shm_cleanup_wrapper, 
apr_pool_cleanup_null);

... where pool is the first parameter to post_config (and used to 
create shmseg);



> I put the new version at 
> <http://apache.org/~sctemme/mod_example_ipc.c> to save on e-mail 
> bandwidth.
>
> Thanks again,
>
> S.
>
> -- 
> sander@temme.net              http://www.temme.net/sander/
> PGP FP: 51B4 8727 466A 0BC3 69F4  B7B8 B2BE BC40 1529 24AF


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