[mod_python] Problem keeping persistent object in memory (global)

Huzaifa Tapal huzaifa at hostway.com
Mon Jun 6 13:02:48 EDT 2005

One option that I use is to create a singleton in the module that I want 
to be global at the first import of that module.  So lets take your 
mySitePool module for example:

class mySitePool:
    def __init__(self):
          ' suite


global mysitepool
mysitepool = mySitePool()

Now, in your mod_python request handler, when you add the import of 
mySitePool, the global singleton object of mySitePool will be created. 
Since, the module is imported, in mod_python, that module will be cached 
so it would not get imported again so to recreate the singleton.

So your handler would look like this:

import mySitePool

def handler(req):
    mySite = mySitePool.mysitepool.get()
    return mySite(req)

Let me know if this helps.


Sébastien Arnaud wrote:

> Hi,
> I have attempted to write my own little framework ("heracles" I named  
> it;) to develop applications faster using mod_python and it is coming  
> along great. Mainly I am using the framework to keep handy a bunch of  
> little utils functions/objects I have written along the years while  
> working with mod_python, such as a pool of connections for DB  
> connections, XML/XSLT rendering, Cheetah template rendering, etc...
> I am hitting the wall on a very stupid problem that I thought I had  
> working. I can't get an object declared as global to remain in memory...
> Under Apache Pre-fork MPM model, this I understand, but under the MPM  
> Worker model, where I specify to start 10 threads in one process, I  
> kind of don't get it... Maybe some of you will be able to spot what I  
> am doing wrong.
> Basically, what I am trying to do is to keep the object mySitePool in  
> memory since each Site object (heracles.site) has everything needed  
> by a thread to process a request. At the first request the mySitePool  
> object should get initialized, but for any other requests it should  
> be simply the matter of retrieving one Site object via the Queueing  
> mechanism to process one request. Right now the problem is that I am  
> able to see for each request one entry in the apache log file that  
> the mySitePool is being initialized...
> Thank you in advance for any pointers or solutions you may have!
> Apache2 config (MPM worker):
> ---------------------------
> <IfModule worker.c>
> StartServers         1
> MaxClients          10
> MinSpareThreads     10
> MaxSpareThreads      0
> ThreadsPerChild     10
> MaxRequestsPerChild  0
> </IfModule>
> Apache2 mod_python (.htaccess):
> -------------------------------
> PythonInterpPerDirective On
> PythonOption "SiteName" "Heracles Test site"
> PythonOption "SiteDescription" "Testing the framework!"
> PythonOption "SiteVirtualPath" "/heracles/"
> PythonOption "SiteViewPath" "/xxx/webapp/views/"
> PythonOption "MySQLhost" "xxx"
> PythonOption "MySQLuid" "arnaudsj"
> PythonOption "MySQLpwd" "xxx"
> PythonOption "MySQLdb" "test"
> SetHandler python-program
> PythonHandler heracles.site::handler
> PythonDebug On
> PythonAutoReload On
> heracles.site.py:
> -----------------
> [...]
> def handler(req):
>     """
>     Standard mod_python handler code for Heracles Web Application  
> Framework
>     The SitePool is initialized based on Apache MPM setting
>     """
>     global mySitePool
>     try:
>         mySite = mySitePool.get()
>     except NameError:
>         req.log_error("Initializing Heracles WAF at %s with %s thread 
> (s)" % (req.document_root(), apache.mpm_query(6)))
>         mySitePool = Pool(Constructor(Site, req), apache.mpm_query(6))
>         mySite = mySitePool.get()
>     return mySite(req)
>     mySitePool.put(mySite)
> [...]
> Cheers,
> Sébastien
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