[mod_python] The DOs and DONTs of mod_python

Philippe C. Martin wrote:

> Since I just managed to seg fault apache I feel I should explain what my goal 
> is with mod_python.
> 
> I already have a fairly big library written in python which purpose is to 
> discuss with smart cards but also provide "software" enryption capabilites: 
> As such, this library uses modules that in turn talk to C code.
> 
> The ultimate goal is to have users need to authenticate themselves to the 
> servers (on smart card on each side) in order to obtain access to certain 
> pages.
> 
> I must also say that there is a failry large data set that needs to be loaded 
> in memory.

Why?

> The code below shows the line that creates the core dump: it instantiates that 
> _large_ object and does a lot in the process.
> 
> As I am an application developper more than a web guy, there are perhaps some 
> obvious "NO NOs'" I should be aware of that are related to the apache 
> environment.
> 
> Please note that, although I must have bugs, the code I'm calling _seems_ to 
> work flawlessly under Linux and Windows.

It might, for a single interpreter. But apache might be forking multiple 
children on your system. Can your machine handle 5 or more copies of 
this object in memory?

> from mod_python import apache
> import os
> import sys
> if os.name == 'nt':
>      sys.path.append("Z:\\dev")
> else:
>      sys.path.append('/home/philippe/dev')
> 
> 
> from SC.pilot.SC_Script_Processor import *

This may happen multiple times. It will be cached in a prefork 
environment, but once for each child. I have no idea how it works on 
Windows.

> def world(req):
>      ls = SC_Script_Processor() #INSTANTIATE A _BIG_ OBJECT ==> *** THIS IS 
> THE KILLER THAT CRASHES APACHE ***

How big? If it's a data set, why not use a database?

>      ll = ls.Reader_List() # get the reader list
> 
>      #Grab ATR from card - assume first reader
>      l_appli_conn = ls.Get_Connection(r1)
>      
>      req.send_http_header()
>      req.write("RETURN CARD ATR= " +  l_appli_conn.Get_Connection_ATR() )
>      return apache.OK

We need to see your code in the imported module. It's a black box to us.