[mod_python] sys.path shared?

You certainly can't share a database connection across apache children 
using a forking model, and I haven't decided if I think you can using a 
threaded mpm either.  You probably don't want the interpreter shared at 
all, b/c of the good ol' GIL.  Also, if you use psycopg (afaik, the 
only threadsafety level 2 adapter), you're really opening a new 
connection each time you grab a cursor - it just handles the magic for 
you.  In fact, you've gotta be pretty careful using psycopg if you dont 
want it to hold a gangload of connections open for no reason.

If you are globally setting sys.path in apache conf, you know that each 
instance of mod_python is _beginning_ with the same sys.path (or maybe 
each req - i forget things alot).  If you have some code which modifies 
it, it won't propogate.  You could take a look at the code for 
application variables in PSE[1] and copy the general idea (think of app 
vars as session vars that span sessions the way session vars span 
requests).

We also hacked up a way of holding onto a db connection, but only 
per-apache process.  This isn't too bad, because you can handle several 
hundred requests before tearing down the child (and, in a shared env, 
the connection is only opened after the first mod_python req comes 
through).

Cheers,

-=JR

[1] http://nick.borko.org/pse - it's totally fly

On Sep 22, 2004, at 8:58 AM, Brian Bird wrote:

> Not sure that's actually evidence against threads. In my case I do 
> actually
> want to share variables (I want only one database connection shared 
> across
> all requests and I also have a global variable counting the number of
> requests which each reuqest updates)
>
> I've got my sys.path set up in the apache config so it only has to be
> initialised once. The (potential) problem with forking is the amount of
> extra overhead required for each request. Mind you, apache seems to do 
> a
> pretty good job of reducing the overhead so it's not really a problem. 
> But
> to share something like a database connection using a forking model... 
> I'm
> not sure that's even possible is it?
>
> Brian
>
> -----Original Message-----
> From: mod_python-bounces at modpython.org
> [mailto:mod_python-bounces at modpython.org] On Behalf Of Terry MacDonald
> Sent: 22 September 2004 14:38
> To: mod_python user mailing list
> Subject: RE: [mod_python] sys.path shared?
>
>
> ah-ah! More evidence against threads in the threads versus processes 
> debate.
> ;3)
>
> On Wed, 2004-09-22 at 14:10, Brian Bird wrote:
>> Sorry, I should have given this a bit more thought. If you're using a
>> forked process environment then I would expect the sys.path variables
>> to be separate for each request. If you're using a threaded mpm (which
>> is what I
>> use) then I assume sys.path would work like global variables which are
>> shared across requests.
>>
>> Brian
>>
>> -----Original Message-----
>> From: mod_python-bounces at modpython.org
>> [mailto:mod_python-bounces at modpython.org] On Behalf Of Terry MacDonald
>> Sent: 22 September 2004 13:54
>> To: mod_python user mailing list
>> Subject: RE: [mod_python] sys.path shared?
>>
>>
>> Can anyone put me right on my understanding of the way mod_python
>> works in an apache forked process environment.  Each process has its
>> own embedded interpreter and therefore its own sys.path variable.
>>
>> How is it possible for an apache instance/process with its own
>> embedded interpreter to 'reach' across and use/inherit another
>> processes/interpreters sys.path?
>>
>>
>>
>> On Wed, 2004-09-22 at 09:58, Brian Bird wrote:
>>> Might be best to try it: Write a cgi script which prints the
>>> sys.path
>>> at the start and at the end. Put a long sleep in the middle then you
>>> can visit your script twice with a browser (start the second visit
>>> while the first one is still running) and see what the sys.path is of
>>> your second visit.
>>>
>>> My gut feeling would be that it would be possible but I'm pretty new
>>> to mod_python so I wouldn't rely on that! :-)
>>>
>>> Brian
>>>
>>> -----Original Message-----
>>> From: mod_python-bounces at modpython.org
>>> [mailto:mod_python-bounces at modpython.org] On Behalf Of Terry 
>>> MacDonald
>>> Sent: 21 September 2004 23:44
>>> To: mod_python user mailing list
>>> Subject: Re: [mod_python] sys.path shared?
>>>
>>>
>>> Each apache instance/process has its own interpreter therefore its
>>> own
>>> sys.path.  So I would say it is not possible.
>>>
>>> On Tue, 2004-09-21 at 23:24, Adrian Holovaty wrote:
>>>> I have mod_python code that appends a directory to sys.path and
>>>> deletes that directory from sys.path at the end of the handler. Is
>>>> it possible that, between that push and pop, another Apache
>>>> instance running the same code
>>
>>>> might get the non-popped sys.path, making its sys.path out of sync
>>>> with
>>> the
>>>> other Apaches?
>>>>
>>>> Adrian
>>>> _______________________________________________
>>>> Mod_python mailing list
>>>> Mod_python at modpython.org
>>>> http://mailman.modpython.org/mailman/listinfo/mod_python
> -- 
> Terry
> Registered Linux User # 311806
> www.taumu.com
>
>
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