[mod_python] stumped by inputfilter infinite repeat

Ken Manheimer ken.manheimer at gmail.com
Mon Aug 20 18:39:33 EDT 2007

On 8/18/07, Graham Dumpleton <graham.dumpleton at gmail.com> wrote:
> Which version of mod_python and Apache are you using?
> The Tramline author suspected there existed a problem in mod_python
> and/or Apache that caused some issues. They suggest in their
> documentation a change that should be made to mod_python, although it
> hasn't been done in official releases as it wouldn't seem to be the
> correct thing to do. One issue was fixed in filter code in mod_python
> in recent versions which may have caused issues, but not the same
> change they suggested. They also felt that certain older versions of
> Apache may have had some problem.
> For some more details see:
>   https://issues.apache.org/jira/browse/MODPYTHON-76

thanks much, graham, for your reply.  i did know about the need to
inihbit filter.flush() - it's described in the tramline install
instructions.  i also factored tramline completely out of the picture,
reproducing the behavior using instead some trivial artifical
inputfilter and outputfilter functions:

  def inputfilter(filter):
      "stub input filter"
      filter.req.log_error("klm input filter")

  def outputfilter(filter):
      "stub output filter"
      filter.req.log_error("klm output filter")

running without pdb enabled but through the rewrite rule i mentioned
earlier, to Zope, yields an infinite stream of the "klm input filter"
messages, and no "klm output filter" ones.  (the problem does *not*
happen when the Zope backend is not running.)

i did reread the bug report, and it occurred to me to try the current
apache svn version, as the bug report mentions - an off chance,
though, since the features of the svn version around the time of the
bug report should have seen released by now.  unfortunately, that
works worse.  i'm getting a fatal error trying to run the latest svn
version with mod_python installed:

httpd: Syntax error on line 116 of /usr/local/apache2/conf/httpd.conf:
Cannot load /usr/local/apache2/modules/mod_python.so into server:
/usr/local/apache2/modules/mod_python.so: undefined symbol:
err 1:  2811  /usr/local/apache2/bin/apachectl configtest

this obstacle on obstacle is discouraging.  a google search reveals no
other reports of this particular error, and i have no reason to be
confident that getting it working would actually improve the original
inputfilter problem.  i plan to inquire on the tramline and plone
lists for alternatives.  i am interested to hear insights on this, but
think i'm better off pursuing other avenues (there's some alpha plone
accommodations for blobs in the zodb), and if that works, giving up on

i did solve one interesting incidental problem along the way, that
might be of value to someone else.  when the interminable inputfilter
invocation is happening i have to kill apache with a KILL signal (9).
doing that lead to mutex leaks, soon leading to apache start failures,
with an error_log complaint like this:

[Fri Aug 17 12:00:00 2007] [error] (28)No space left on device:
mod_python: Failed to create global mutex 0 of 32 (/tmp/mpmtx125450).

investigating, i learned about ipcs to report semaphores and ipcrm to
remove them, and created a little script that did the job for me:

ipcs -s | while read key id garbage; do
  case "$id" in
    [0-9]* ) echo -n "$id "
             ipcrm -s $id;;
    * ) : ;;


also, in case anyone still thinks attention to mod_python and tramline
is worthwhile, here are my web server details, from mod_python's

  Apache/2.2.4 (Unix) mod_ssl/2.2.4  OpenSSL/0.9.7a  DAV/2  mod_python/3.3.1

and host server os and hardware: linux kernel 2.6.9-42.ELsmp on an AMD
Athlon 64 X2
Dual Core Processor 4200+.  (it's actually running redhat 4.1, alas.)


> On 19/08/07, Ken Manheimer <ken.manheimer at gmail.com> wrote:
> > hi, all.  i'm using mod_python with a downloads/uploads handler,
> > tramline ( http://infrae.com/products/tramline ) with a content
> > management system (plone).  when the tramline input and output filters
> > are hooked in (using SetInputFilter and SetOutputFilter) and i visit
> > the zope/plone site via a redirect, i get infinite repeated calls to
> > the input filter.  (i can observe the this by setting PythonEnablePdb
> > - from the perspective of the web browser, no page is returned.)  i
> > can provide more details, and realize that this may be a tramline
> > problem, but it seems like a behavior that might be familiar to
> > mod_python experts, so i thought i'd run it by you all first.
> >
> > things like mpinfo and mptest.py work fine.  visiting the regular,
> > file-based mockup site yields no problems - only the embedded zope
> > site, via a rewrite rule:
> >
> >   RewriteRule ^/testbed(.*)
> >{HTTP_HOST}:80/VirtualHostRoot/_vh_testbed/$1
> > [L,P]
> >
> > (the elaborate VirtualHostRoot stuff is for a zope virtual hosting provision.)
> >
> > does any of this sound familiar to anyone?  suggestions about
> > debugging it?  (stepping through the input and output filters using
> > PythonEnablePdb yields little or no illumination - they just keep
> > getting invoked.  i don't know what to look for tracing added to
> > importer.py FilterDispatch, which i tried instead of using
> > PythonEnablePdb.)
> >
> > any help would be appreciated!

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