[mod_python] Circular references starting from the request object are not collected

workaround: use a weakref for one side of the circular reference.

import weakref
req.foobar = weakref.ref(myfoobar)


> Hi,
>
> I'm running Apache 2.0.50, mod_python 3.1.3 with Python 2.3.4 on Windows
> XP
> Pro and Windows 2000 server.
>
> I finally found a source for the memory leaks I have been observing for a
> while now : if you store an object in the request object that reference
> directly or indirectly the request object itself, it builds a circular
> reference. This circular reference does not seem to be garbage collected.
>
> The test handler :
>
> from mod_python import apache
>
> def handler(req):
>     # req.foobar=req
>     req.content_type='text/html'
>     req.write('OK')
>     return apache.OK
>
> I used Apache Benchmark :
>
> ab -c 5 -n 100000 http://localhost/test.py
>
> With the comment line, everything is OK, I do not see any memory leak.
>
> If I uncomment the 'req.reqs=[req]' line, the memory leak shows up. My
> Apache process normally uses around 20 MB without the comment, and in 30
> seconds of running the above handler (comment removed) with the above
> Apache
> Benchmark command, it reaches 125 MB !
>
> Normally, circular reference are collected by the garbage collector of
> Python, but unfortunately when defining object from C, you have to do a
> few
> tricks to support this :
>
> http://www.python.org/doc/2.3.4/api/supporting-cycle-detection.html
>
> It seems that this is not done in mod_python, by having a look at
> requestobject.c.
>
> I find this quite a big problem, and I don't find any workaround except
> "Don't reference the request object from anywhere that might be referenced
> by the request object", which is a pretty big limitation, quite annoying
> in
> the application I'm building.
>
> Best regards,
>
> Nicolas Lehuen
>
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