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Graham Dumpleton
graham.dumpleton at gmail.com
Wed Dec 10 22:25:27 EST 2008
2008/12/11 Jean Lagarde <jean.lagarde at gmail.com>: > Thanks Graham, > The difference is very clear now. > Yes I agree that performance with mod_python is not optimal, but for now > it's a compromise because I'm using an existing product > ( http://www.infrae.com/products/tramline -- I know there's been other > questions about this product on this list before). The question came up > because there's a couple of branches of it around and I wanted to understand > what was going on. Hmmm, are they still claiming mod_python needs to be patched? I can't remember the change they were saying needed to be made, but couldn't see how that change fixed anything. A different change was made for another issue in code which was found when investigating their change, but not sure I ever got back any conclusive response as to whether that addressed problem. There ticket related to that is: http://issues.apache.org/jira/browse/MODPYTHON-76 Tramline was a good example of something that should have been a Apache C module. I wouldn't be surprised actually if one already did exist that does the same thing. Graham > -- Jean > > On Wed, Dec 10, 2008 at 2:13 AM, Graham Dumpleton > <graham.dumpleton at gmail.com> wrote: >> >> 2008/12/10 Jean Lagarde <jean.lagarde at gmail.com>: >> > Hi all, >> > The subject says it all. The documentation seems a little sparse on the >> > topic. The description of pass_on is: >> > Passes all data through the filter without any processing. >> > >> > The description of disable is: >> > Tells mod_python to ignore the provided handler and just pass the data >> > on. >> > (which also states that mod_python uses that one internally). >> > "passes all data through" and "just pass the data on" sound like the >> > same >> > thing to me. What is the additional functionality to "ignore the >> > provided >> > handler"? I assume that there is a difference between the two methods >> > and I >> > would like to know what it is no matter how subtle. I'm looking for the >> > most >> > CPU efficient way to decide early on in the execution of a filter that >> > we >> > don't want to filter a particular request in any way, but maybe >> > understanding the difference would help me to make a better use of >> > mod_python filters in other ways. >> > I did try to use both in code, and on one server with one version of >> > Apache >> > 2 (and other components) it seemed to make no functional difference >> > (although I did not attempt to closely measure CPU usage), whereas on >> > another server with an earlier version of Apache 2 (and other >> > components), >> > using disable() caused no error, but dropped values from POST forms >> > passed >> > on to PHP scripts. >> > Thanks for any info. I did search the lists, but only found one comment >> > on >> > someone's code from Graham that "Normally 'filter.pass_on()' would be >> > used >> > here, not 'filter.disable()'", but without explaining why. >> >> If you use disable(), your filter will never be called for that >> request (input or output as appropriate) again. >> >> If you use pass_on(), then it is passing on data available to that >> specific call to your filter function. >> >> The distinction exists because your filter function can be called >> multiple times for a request. The latter is allowing you to pass on >> the data for that call, but still allowing you the option to process >> data in a subsequent call of the filter function. >> >> The disable() call is used internally to mod_python to ensure that >> filter function is never called again for a specific request if the >> filter function itself raises an exception of some sort. If it doesn't >> do this you could end up with a loop if the error in filter function >> actually generates output, for which it would then call the filter >> function again, etc etc. >> >> FWIW, if you are concerned about performance in any way, then you >> shouldn't be using mod_python to implement Apache input/output >> filters. Yes you can write filters with mod_python, but it will impact >> performance. For best performance you should write filters in C code >> as proper Apache module. >> >> Graham > > > _______________________________________________ > Mod_python mailing list > Mod_python at modpython.org > http://mailman.modpython.org/mailman/listinfo/mod_python > >
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