[mod_python] Shared global variables among apache children?

Read:

  http://www.dscpl.com.au/articles/modpython-004.html

It gives a bit of background about different MPM models and mod_python.

Also, be aware that the global variable you are using as counter will be
reset back to 1 in a process if that module gets automatically reloaded.
This is because new module gets reloaded on top of the old. You might
also therefore read about some of the issues with module reloading.

  http://www.dscpl.com.au/articles/modpython-003.html

Graham

Joshua Ginsberg wrote ..
> Geez, there are a lot of questions about IPC this week... :-/
> 
> Justin --
> 
> Let's say you open two terminals, and in each you run a python
> interpreter. In the first, you tell it:
> 
> >>> x = 3
> 
> And in the second you tell it:
> 
> >>> x = 3
> 
> And then back in the first you tell it:
> 
> >>> x += 1
> 
> And then in the second you tell it:
> 
> >>> print x
> 
> What are you going to get? 3 of course -- not 4. Duh! That's because
> they're separate processes. Separate memory spaces. Totally independent.
> It's the same thing with Apache. Each Apache process runs with its own
> unique memory space and its own unique Python instance.
> 
> So solve this problem the same way you'd solve it with two separate
> Python interpreter processes. Examples:
> 
> 1) Use files and locks.
> 2) Use something like SQL that has locking built in.
> 3) Use some IPC protocol -- XMLRPC or (hehe) D-BUS
> 
> But if you want a purely multithreaded web server that has one big
> shared memory space, use AOLServer or something like that. Apache was
> originally designed to do forking and lots of it. It's only recently
> that it has been developing MPM models that have multiple connections
> handled by a process with multiple threads, and this doesn't happen the
> same way in all MPMs or on all platforms.
> 
> -jag
> 
> On Thu, 2006-08-10 at 14:08 -0500, justind wrote:
> > It feels like I'm missing either one configuration option or this may
> > not even be possible.
> > 
> > I have this little bit of code. I expected, that every 4 seconds that
> x 
> > would increment by 1 on the returned page. It does. However I think that
> > this same code is loaded into each child process (correct me if I'm 
> > wrong) of apache.
> > Depending on which child I get, and when they were launched (hitting
> > refresh rapidly on Firefox seems to demonstrate this too me) I get a
> > different page back. One will show 4 then a refresh will show 3, another
> > will show 3, another will show 4 and so on and so forth.
> > 
> > I guess my question is, how can I share the global variable of x among
> > all the apache child processes, or is this really my problem)?
> > 
> > Any help would be very appreciated.
> > 
> > Code follows below:
> > 
> > from mod_python import apache
> > import time
> > import thread
> > 
> > x = 1
> > 
> > def handler(req):
> >     global x
> >     req.content_type = 'text/plain'
> >     req.write("Hello World! " + str(x))
> >     return apache.OK
> > 
> > def do_me():
> >     global x
> >     while True:
> >         time.sleep(4)
> >         x += 1               
> >                
> > thread.start_new(do_me,())   
> > _______________________________________________
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> > Mod_python at modpython.org
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> 
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