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From "Graham Dumpleton" <grah...@dscpl.com.au>
Subject Re: get_session(), req.session, req.form and MODPYTHON-38
Date Tue, 14 Mar 2006 01:12:02 GMT
Jim Gallacher wrote ..
> The idea of something like req.get_session() is to give users an obvious
> way to grab a session object without the deadlock concerns. How many 
> times have we seen this kind of problem-code on the mailing list?
> 
> def index(req):
>      sess = Session.Session(req)
>      do_stuff(req)
>      ...
> 
> def do_stuff(req):
>      sess = Session.Session(req)
>      ... do other stuff.
> 
> Having the session constructor check for the existence of req.session is
> of no use here. We need a way to make sure only *one* session instance
> is created per request. (Bonus marks for making it work with internal 
> redirect).

FWIW, I use the following in a class based authenhandler.
        
        thread = threading.currentThread()
        
        if self.__cache.has_key(thread):
            req.session = self.__cache[thread]
        else:
            req.session = Session.Session(req)
        
            self.__cache[thread] = req.session
            def cleanup(data): del self.__cache[thread]
            req.register_cleanup(cleanup)

In short, store it in a cache outside of the request object keys by
the thread ID.

Works for both internal redirects and also for fast redirects as used by
DirectoryIndex matching algorithm, although for the latter there are
other issues as I have documented in MODPYTHON-146.

My thinking keeps changing a bit, but overall I have been leaning
towards not having a get_session() like function explicitly provided and
instead documenting how to correctly write a authenhandler which can
handle form based login with sessions. Ie., use Apache phases properly
rather than pushing authentication into content handler phase as most
do. Unfortunately, I keep finding things in mod_python that need to
be improved or fixed to avoiding having to fudge things, thus haven't
presented my code for others to look at yet. :-(

Graham

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