After importing PySide multiprocessing pool hangs on numpy dot

otognan

I've got this very peculiar hanging happening on my machine when using pytnon multiprocessing Pool with numpy and PySide imported. This is the most entangled bug I have seen in my life so far:) The following code:

@import numpy as np
import PySide

def hang():
import multiprocessing
pool = multiprocessing.Pool(processes = 1)
pool.map(f, [None])

def f(ignore):
print('before dot..')
np.dot(np.zeros((128, 1)), np.zeros((1, 32)))
print('after dot.')

if name == "main":
hang()
print('success!')@

hangs printing only 'before dot..'. But it is supposed to print
@
before dot..
after dot.
success!@

so it hangs inside dot function.

There are several magical modifications I can do to prevent hanging:

if you decrease shape of arrays going into 'dot' (e.g. from 128 to 127)

(!) if you increase shape of arrays going into 'dot' from 128 to 256
if you do not use multiprocessing and just run function 'f'
if you comment out PySide import which is not used anywhere in the code

Any help is appreciated!

Packages version:

numpy=1.8.1. PySide=1.2.1 or 1.2.2

Python version:

Python 2.7.5 (default, Sep 12 2013, 21:33:34) [GCC 4.2.1 Compatible Apple LLVM 5.0 (clang-500.0.68)] on darwin

or

Python 2.7.6 (default, Apr 9 2014, 11:48:52) [GCC 4.2.1 Compatible Apple LLVM 5.1 (clang-503.0.38)] on darwin

Albert Zeyer

Is it really numpy.dot or could it also be numpy.zeros?

I am allocating a huge 3d matrix via numpy.zeros and I seem to have a deadlock in some cases there too.