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From fredk2 <fre...@gmail.com>
Subject Re: mod_jk --enable-prefork
Date Mon, 10 Sep 2007 19:37:11 GMT

Many thanks for your reply.
Is it always implied that if an apache module is deemed 'thread safe' it
also implies that it will work in "prefork" environment maybe at the cost of
raw performance ?

Thanks again - Fred


Rainer Jung-3 wrote:
> 
> fredk2 wrote:
>> Hi,
>> 
>> The documentation for  mod_jk (eg. version 1.2.25) about --enable-prefork 
>> says:
>> 
>> "In case you build mod_jk for a multi-threaded Apache httpd 2.0/2.2 MPM
>> (Multi-Processing Module), some areas of mod_jk code need to be
>> synchronized
>> to make it thread-safe. Because configure can not easily detect, whether
>> your are using a multi-threaded MPM, mod_jk by default is always build
>> thread-safe for Apache httpd 2.0/2.2. If you are sure, that your MPM is
>> not
>> multi-threaded, you can use "--enable-prefork" to force the removal of
>> the
>> synchronization code (thus increasing performance a bit). For instance,
>> the
>> prefork MPM is not multi-threaded. For Apache httpd 1.3 this flag will be
>> set automatically."
>> 
>> 
>> If you specify apxs, doesn't it require a config_vars.mk which has a
>> value
>> pair MPM_NAME = prefork  and thus configure could know that prefork was
>> used?
>> Alternatively assuming that apxs is in the same directory then 'httpd -V'
>> could tell that 
>> "Server MPM:     Prefork"
> 
> You are right: "apxs -q MPM_NAME" would do the trick. I didn't find that 
> one, thanks. On the other hand, we would still need to manage a list of 
> MPMs (which MPM on which platform is single-threaded) and there is some 
> danger, that people have more than one mpm installed (like on many linux 
> distros) and compile against prefork, later use against worker. All in 
> all I'm still in favor of building thread safe by default and only when 
> explicitely requested removing the thread synchronization.
> 
>> The question I have: if the Apache httpd v2.2 is prefork and the mod_jk
>> is
>> compiled "default threaded", are there any potential instabilities? (on
>> Solaris and Linux)
> 
> No, not that we aware of any. On both platforms, the default was 
> building thread safe for a long time. We use pthread mutexes and no 
> problems have been reported with those.
> 
>> Many thanks - Fred
> 
> Regards,
> 
> Rainer
> 
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> 
> 

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