Justin Bronn wrote:
>> Based on comments in a separate thread, GeoDango may have issues with
>> multithreaded configuration. Which Apache MPM was being used for each
>> Apache version, prefork or worker? The worker MPM uses threads and so
>> that could be the culprit.

> Yes -- the libraries GeoDjango uses, GEOS and GDAL, are not thread
> safe.  Thus, it is highly recommended to use the prefork version of
> Apache.

>> In a Python Shell, I am able to perform queries on my spatial models
>> successfully.  In a web browser, I get a plain white screen if any
>> code is executed that works with spatially enabled models.

> I created an Ubuntu 8.10 VM to try and test out this problem.
> However, the only way that I could reproduce your exact problem
> (segfault upon HTTP request) is when using the mpm-worker (threaded)
> Apache.  When using the prefork, however, I was able to get both
> mod_python and mod_wsgi to work with a simple demonstration app [1].
> I think mpm-worker is the default when you do `apt-get install
> apache2`, so make sure you have it removed, e.g., `apt-get remove
> apache2-mpm-worker; apt-get install apache2-mpm-prefork`.

> BUT, I found another issue -- while I could login to and browse the
> admin interface, whenever I tried to view a geographic model an
> exception would get raised (but no segfault) deep in the admin widgets
> [2], crashing the app.  While this crash occurs in 8.10 it does _not_
> happen in my 8.04 VM.  Thus, this leads me to believe that it may be a
> manifestation of the same troubles you're experiencing.  Moreover,
> this admin crash happens with _both_ mod_python and mod_wsgi in 8.10
> (mod_wsgi configured with `threads=1`).

> Needless to say, this behavior has me perplexed at the moment, and due
> to my finals I'm not going to have a lot of time to dig in deeper
> until next month.  Perhaps there's a clash of the libraries that are
> linked to Apache and the ones used by the packaged versions of GEOS/
> GDAL, or maybe it's caused by Ubuntu's AppArmor (confined to just CUPS
> in 8.04) -- but these are just potential possibilities.

>> Justin was good enough to run a test case I created and was unable to
>> duplicate the error.  I'm wondering now about the exact versions of
>> Apache and other components that might be causing the problem.

> I still have the CentOS 5.2 VM, and I'll test it out again, but I'm
> not sure yet that this could be the same issue as you reported in
> October.  It's a different distribution that used significantly older
> versions (that also worked in my tests).

> [1] http://geodjango.org/hg/world
> [2] http://code.djangoproject.com/browser/django/trunk/django/contrib/gis...