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Running nosetests with multiprocessing tests on Windows leads to infinite explosion of processes #407

jpellerin opened this issue Dec 14, 2011 · 3 comments


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Create the following two files in a directory:

== =================
from nose import main
if name == 'main':


== ==================
from multiprocessing import Pool
import os, time

def foo(x):
return (x, os.getpid())

def test_me():
pool = Pool(processes=4)
x =, range(10))
a, b = zip(*x)
print a, b
assert list(a) == range(10)

assert 1 < len(set(b)) <= 4

On Windows, if I go to the directory and type


...the tests run correctly. If I type

nosetests causes an exponential explosion of processes

(Note, be careful if you try it, in my case I need to have a command window open with "taskkill /F /IM python.exe" ready, otherwise the computer locks up fairly quickly.)

This does not seem to be entirely nose specific since "python test" seems to do the same thing in my project. But I'm wondering if you have any insight into what's going on here.

Python 2.7, Windows 7, version 1.0.0

See for more information.

Google Code Info:
Issue #: 398
Created On: 2011-02-18T21:48:33.000Z
Closed On:

@ghost ghost assigned jpellerin Dec 14, 2011
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Sorry, forgot to mention: What seems to be happening in both cases ("nosetests" and "python test") based on the printed output is that each multiprocessing.Process that gets started executes the original command line ("nosetests" or "python test"), so each process starts running the test suite, causing an infinite fan-out.

Google Code Info:
Created On: 2011-02-18T22:34:05.000Z

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You can work around this issue by using:
python.exe -c "import nose; nose.main()"
instead of nosetests

Note that nose.main() with no args parses sys.argv

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@jpellerin I have had the same problem as you. We were seeing this running through buildbot. I have yet to get the workaround to work in buildbot that @chrisejones has provided.

We run the buildbot on both a Windows 7 64-bit environment and a Red Hat 5 64-bit environment both running Python 2.7.3. The Red Hat experiences no problems but the Windows 7 exhibits the same issue you have described. We have also tested with nose 1.1.2 and nose 1.3.0 and both exhibit this behavior.

The workaround will be ok for now as long as I can make it work with buildbot. Hopefully, this will get fixed soon.

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