#6648: random seed identical among preforked FastCGI instances
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Reporter: [EMAIL PROTECTED] | Owner: nobody
Status: new | Component: Uncategorized
Version: SVN | Keywords: random seed fastcgi fcgi prefork
Stage: Unreviewed | Has_patch: 0
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While writing a basic captcha module, I was encountering a lot of
duplicate strings of "random" text that I could not explain. Then I
remembered seeing this comment on a separate session issue:
http://code.djangoproject.com/ticket/1180#comment:20
Based on that info, I setup some extra logging, and it did appear that
each of my FastCGI threads were producing identical random values. I was
specifically using a call like this:
random.choice('ABCDEFGHIJKLMNOPQRSTUVWXYZ'). It's possible other random
methods are not affected, I was only interested in that one. It seems the
random seed is set prior to the fork, and each forked process thereafter
produces identical random output as a result.
In my setup, I run manage.py with method=prefork, runfcgi, and a static
number of processes. This is on an Ubuntu Gutsy AMD 64-bit (on Xen) with
Python 2.5.1. I'm currently running against SVN Django, revision 7049.
My workaround was to add a middleware class with an init function that
sets the random seed. This gets called at "startup" in each of the new
FCGI processes, giving them unique random output. Obviously not ideal, but
it gets the job done in my case.
{{{
import logging, logging.config
import os, random, time
class ReseedRandom(object):
def __init__(self):
logging.debug("setting new random seed for this process")
random.seed("%d%s" % (os.getpid(), time.ctime()))
}}}
It would be much cleaner if the manage.py FCGI launcher could seed its
random number generator AFTER the fork occurs, rather than before (or not
at all, as the case may be).
--
Ticket URL: <http://code.djangoproject.com/ticket/6648>
Django Code <http://code.djangoproject.com/>
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