GIL + Cython + Subprocess freeze

freeze_in_subprocess.py

from test import zero

from functools import wraps
from multiprocessing import Process, Queue


def queue_result(function, queue):
    @wraps(function)
    def decorated_function(*args, **kwargs):
        has_raised = False
        try:
            to_ret = function(*args, **kwargs)
        except Exception as e:
            has_raised = True
            to_ret = str(e)
        queue.put(to_ret)
        queue.put(has_raised)
    return decorated_function


def run_in_subprocess(function):
    @wraps(function)
    def decorated_function(*args, **kwargs):
        queue = Queue()
        process = Process(target=queue_result(function, queue),
                          args=args, kwargs=kwargs)
        process.start()
        process.join()
        to_ret = queue.get()
        has_raised = queue.get()
        if has_raised:
            raise Exception(to_ret)
        else:
            return to_ret
    return decorated_function


def zero_in_subprocess(in_parallel):

    @run_in_subprocess
    def sub_test():
        zero(10, in_parallel)
        return 1

    print zero(10, in_parallel)
    print [sub_test() for _ in range(10)]


zero_in_subprocess(False)  # it doesn't freeze
zero_in_subprocess(True)  # it freezes

# Expected results would be:
# 0
# [1, 1, 1, 1, 1, 1, 1, 1, 1, 1]
# 0
# [1, 1, 1, 1, 1, 1, 1, 1, 1, 1]
# but the last output will never come :(

setup.py

from distutils.core import setup
from Cython.Distutils.extension import Extension
from Cython.Build import cythonize
from Cython.Distutils import build_ext

import numpy as np

ext_modules = [Extension("test",
                         ["test.pyx"],
                         include_dirs=[np.get_include()],
                         language='c++',
                         extra_compile_args=['-fopenmp'],
                         extra_link_args=['-fopenmp']
                        )]

setup(
    name='test',
    cmdclass={'build_ext': build_ext},
    ext_modules=cythonize(ext_modules),
)

test.pyx

from cython.parallel import prange

def zero(long n=10, in_parallel=False):
    cdef long i

    if in_parallel:
        for i in prange(n, nogil=True):
            pass
    else:
        for i in xrange(n):
            pass
    return 0