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Kevin J. Smith
hockeysk8 at gmail.com
Tue Feb 21 12:46:42 EST 2006
In trying to answer the question of which MPM model the server uses I think I may have come across my answer. In Graham's article http://www.dscpl.com.au/articles/modpython-004.html (not sure why I did run across this article in my many Google searches for an answer) he has explained the behaviour of mod_python with the various MPM models. It is most likely that I am using a prefork model because the server is running out-of-the-box fedora (don't have access to the server at the moment.) And therefore, if I have understood Graham's article correctly, with a prefork model, even though the interpreter may be named the same, different requests may be picked up by different apache child processes therefore they will not be sharing the same memory. To quote from the article: "This ability to access the same global data from any request handler and for that data to persist for the lifetime of that instance of Apache is not present when either of the "prefork" or "worker" modes are used. This is because handlers can be executing within the context of distinct child processes, each with their own set of global data unique to that child process. Further, the global data present within a particular child process only exists for the lifetime of that child process and Apache could shutdown and kill off a child process at any time." This certainly makes sense within the prefork model. I am not sure why it wouldn't work for worker threads because in my mind they should be sharing the same memory? Nonetheless, I need my handler to be portable therefore I will have to implement my own memory cache with something like memcached (http://www.danga.com/memcached/) <http://www.danga.com/memcached/>or the like (Django uses memcached for a similar purpose.) Somebody please correct me if I have any of this wrong. Cheers On 2/21/06, Nicolas Lehuen <nicolas at lehuen.com> wrote: > > Hi Kevin, > > 1) Please give us your full configuration : OS, Python version, Apache > version and the MPM you use. Your problem may be related to the fact > that you are using a forking MPM. > > 2) Are you sure your module is continually reimported ? Do you see > traces in the error log about that ? Your problem may be related to a > bug in your cache code. > > 3) If you want to re-use the importing mechanism that > mod_python.publisher uses, you can have a look at the ModuleCache > class found in mod_python/cache.py. Moreover, this package can be > re-used for all kind of caching issues (see the source code). > > Regards, > Nicolas > > 2006/2/21, Kevin J. Smith <hockeysk8 at gmail.com>: > > Hi, > > > > I have a page controller that all handlers import with "from > > myapp.gui.pagecontroller import PageController". Each handler is a > class > > derived from the PageController. > > > > In the page controller, I have attempted to set up a shared memory cache > for > > all the controllers with code very similar to the following: > > > > #... > > import threading > > > > CACHE_LOCK = threading.Lock() > > cache = {} > > > > def _fillCache(): > > cache['one'] = '1' > > cache['two'] = '2' > > > > class PageController: > > # ... > > def __init__(self): > > #.... > > if not len(cache.keys()): > > CACHE_LOCK.acquire() > > _fillCache() > > CACHE_LOCK.release() > > #... > > > > > > However, I have discovered that this module is continually reimported > > because it ALWAYS calls the _fillCache() function despite all the > handlers > > running within the same interpreter. > > > > I have upgraded to mod_python 3.2.7 noticing that in the change log > there is > > a lot about fixing module import problems but my app is still behaving > the > > same way. > > > > The flow of my app is that all requests are handled by a frontController > > handler (this is explicitly set in the httpd config) which, after > checking > > the session and authentication and what-not and based on the request > path, > > forwards the request onto one of my pageController handlers via > > util.redirect(). If I have followed Graham's notes about module > importing > > correctly, the frontController and pageController classes would be > imported > > via import_module() whereas the actual pageController module is imported > via > > the regular python import mechanism. > > > > I have spent some time reading about the various "uniquenesses" of > module > > importing within mod_python but it hurt my head slightly and I didn't > know > > if most of it reflected the state of affairs in version 3.2.7. From > reading > > Graham's page I don't believe I should have a problem with the > > PageController handler continually being reimported but it certainly > appears > > to be doing just that. > > > > Can someone shed some light on what I may be doing wrong or a possible > > solution to setting up a shared cache within an interpreter? I know > that if > > I run similar code outside of mod_python my cache design works fine. > > > > Cheers > > > > > > _______________________________________________ > > Mod_python mailing list > > Mod_python at modpython.org > > http://mailman.modpython.org/mailman/listinfo/mod_python > > > > > > > > _______________________________________________ > Mod_python mailing list > Mod_python at modpython.org > http://mailman.modpython.org/mailman/listinfo/mod_python > -------------- next part -------------- An HTML attachment was scrubbed... URL: http://mm_cfg_has_not_been_edited_to_set_host_domains/pipermail/mod_python/attachments/20060221/e861bb19/attachment.html
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