Re: [PHP-DEV] Re: [PHP-CVS] cvs: php4 / TODO From: Ulf Wendel (ulf.wendel <email protected>)
Date: 10/13/00

Chuck Hagenbuch wrote:
>
> Quoting Sebastian Bergmann <sb <email protected>>:
> > Bernd Römer is currently building an Application Server framework in
> > native PHP but native support would be better somewhat, I believe.
>
> Could someone define what an application server is? I hear it all the time these
> days, but I'm not sure what it's supposed to provide for me...

Well, the basic idea is to leave the request based architecture and get
over to an event based one. That means you have some kind of permanently
running "server" process that starts "child" processes and offers them
access to certain resources. Such a permanent running process can't be
realized with any CGI programm on the apache. The apache has a request
oriented architecture. It starts child processes whenever it needs one
to handle a request and kills them afterwards (some keep alive but
basically they get killed at some point).

To do web -application- development you have to keep some state
information between certain requests. This is why we have sessions. Our
sessions are quite nice but imagine we could serialize resource links as
well. Think of the fine day that we don't have to reopen a mysql
connection which is a time consumpting task on every request.

How could we get to that point that we can keep resource links withing
requests? We need a permanent running server process that holds and
shares certain resources (resource links, data,...) with its (request
based) child processes. As you can see this would give us a performance
boost as we can widely avoid session data serializing on slow mediums
(filesystem, database, ...).

Turning PHP in such a architecture is a hard job. You basically need
three things: events, a mechanismn that can detect memory leaks and
finally thread safety as one step to provide load balancing features.

PHP has a relatively small thread-safe kernel (Zend) which is surrounded
by a server abstraction layer and lots of PHP modules (libXML, MySQL,
...). PHP has gathered several external libraries over the years just
like a borg. We don't know anything on the reliability (ok,
sometimes...) of these libraries - are they always thread safe, do they
have memory leaks, etc. If we had a permanent running php server process
it must be very robust. Are all of your modules robust or might some of
them tend to leak? We can't say that all of them fill our needs
(thread-safe, no leaks).

That's why fumanchi's (Bernd Römers) attempt with a permanently running
PHP simulating a webserver using some socket functions is damned to be
incomplete and will likely fail. Sorry, fu - that's my honest opinion.
It's like the parser of my api documentaion generator: broken by design
(yes, it will soon be improved...).

Modifying PHP is not easy, I guess it would take two years to do so, not
because the Zend kernel is not prepared to offer us the neccessary
features but because of the external libraries included in php.

Ulf 

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