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From Jeff Trawick <>
Subject Re: current status of loadable MPM changes
Date Thu, 26 Mar 2009 07:39:02 GMT
On Wed, Mar 25, 2009 at 8:53 PM, Nick Kew <> wrote:

> On 24 Mar 2009, at 21:45, Jeff Trawick wrote:
>  something I'm in a relative hurry to get feedback on is this part:
>> 2. retain data
>>   How can MPMs retain data across unload of the DSO?
>> s->process->server_pool userdata
>>   won't work as-is because there's no server_rec in the pre_config hook.
> Is there a need for an API here?  As opposed to the MPM working with
> its own file-scope static variables, for instance?

File-scope static variables don't work for DSOs (for data retained across
unload/reload) since the variables are re-instantiated at reload.

That led to the following idiom in quite a few modules:

const char *userdata_key = "rewrite_init_module";

    apr_pool_userdata_get(&data, userdata_key, s->process->pool);
    if (!data) {
        first_time = 1;
        apr_pool_userdata_set((const void *)1, userdata_key,
                              apr_pool_cleanup_null, s->process->pool);

(This is a simple use with just a flag.)

That's more gory than it needs to be, and MPMs needed this capability in the
pre-config hook, when there is no s->process->pool; hence the need for a

>>   Proposal: Add ap_set_retained_data(key, value),
>> ap_get_retained_data(key) APIs
>>             (implementation detail: it will set/get userdata on pglobal)
>>             Although not necessary, provide ap_get_config_count()
>> (better name!) to
>>             indicate how many passes of config have completed.  (The
>> interface could be
>>             a global variable, but some third-party module would
>> inevitably clear it.)
> Looks fine, if there is indeed a need for it.

Cool...  Note that the final (working) interface is a bit different, where
ap_set_retained_data takes key + length, allocates the space, and returns
the address to the caller.

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