Python GIL and Cython

par.py

from threading import Thread


def busy_sleep(n):
    while n > 0:
        n -= 1


N = 99999999
t1 = Thread(target=busy_sleep, args=(N, ))
t2 = Thread(target=busy_sleep, args=(N, ))
t1.start()
t2.start()
t1.join()
t2.join()

parpyx.pyx

def busy_sleep(int n):
    _busy_sleep(n)


def busy_sleep_nogil(int n):
    with nogil:
        _busy_sleep(n)


cdef inline void _busy_sleep(int n) nogil:
    cdef double tmp = 0.0

    while n > 0:
        # Do some CPU intensive useless computation to waste some time
        tmp = (n ** 0.5) ** 0.5
        n -= 1

seq.py

def busy_sleep(n):
    while n > 0:
        n -= 1


N = 99999999
busy_sleep(N)
busy_sleep(N)

test_parpyx.py

import pyximport
pyximport.install()

import time
from threading import Thread
import parpyx

N = 39999999

t0 = time.time()
parpyx.busy_sleep(N)
parpyx.busy_sleep(N)
print 'SEQ Elapsed: %.4f' % (time.time() - t0)

t0 = time.time()
t1 = Thread(target=parpyx.busy_sleep_nogil, args=(N, ))
t2 = Thread(target=parpyx.busy_sleep_nogil, args=(N, ))
t1.start()
t2.start()
t1.join()
t2.join()
print 'PAR Elapsed: %.4f' % (time.time() - t0)