Random and fork

Stephane Wirtel stephane at wirtel.be
Thu Feb 7 14:29:33 CET 2013


* Julien Le Goff <julien.legoff at gmail.com> [2013-02-06 08:28:24 -0800]:

> Hi everyone,
> 
> Today I came accross a behaviour I did not expect in python (I am using 2.7). In my program, random.random() always seemed to return the same number; it turned out to be related to the fact that I was using os.fork.
> 
> See below a small program that illustrates this. It is easily fixed, but I'm interested in knowing why this happens. Can anybody give me a hint? Thanks!
> 
> import random
> import os
> 
> for i in xrange(10):
>     pid = os.fork()
>     if pid == 0:
>         # uncommenting this fixes the problem
>         # random.seed(os.getpid())
>         print random.random()
>         os._exit(0)
> 
> os.wait()
> -- 
> http://mail.python.org/mailman/listinfo/python-list

If you look at the code of gunicorn, you can see than there is a
random.seed() just after the fork syscall.

Try with that.

Regards,
-- 
Stéphane Wirtel - http://wirtel.be - @matrixise



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