IDLE crash when using multiprocessing on Mac OSX

Question

If I run this simple code in IDLE in Python 2.7.8, it will pop a window saying "The program is still running! Do you want to kill it?".

from multiprocessing import Pool

def foo(x):
    return x**2

if __name__ == '__main__':
    pool = Pool(2)
    pows = pool.map(foo, range(10))
    print pows

Even if I do kill or not (it will ask twice) nothing will happen. I used to use Windows and I've just recently started using Mac OSX (10.9.4), and I don't know if I'm missing something here.

If I run the same code directly in the Python Shell in terminal, it will run fine. Same in iPython notebook. It just won't on IDLE, popping up that message box.

Any ideas? I'd like to keep using IDLE...

here's the log:

INFO:root:10221: Started process
INFO:root:10221: Defined foo
INFO:root:10221: __name__ == '__main__'
INFO:root:10221: pool created

Answer 1

This was a known issue with the previous version of Pycharm. If you upgrade with the latest version now you can safely use multiprocessing within the console of the IDE without running in this issue any longer.

See here for further informations: https://youtrack.jetbrains.com/issue/PY-14969

Answer 2

Ref this: https://docs.python.org/2/library/multiprocessing.html#introduction

Specifically, in the note:

Functionality within this package requires that the __main__ module be importable by the children. This is covered in Programming guidelines however it is worth pointing out here. This means that some examples, such as the multiprocessing.Pool examples will not work in the interactive interpreter."

Here's a similar question Child processes created with python multiprocessing module won't print

Example of logging activity to a file:

#!/usr/bin/env python

import logging
from multiprocessing import Pool
import os

logging.basicConfig(filename='example.log',level=logging.DEBUG)

def log_msg(msg):
    logging.info("{}: {}".format(os.getpid(), msg))

log_msg("Started process")

def foo(x):
    log_msg("running foo")
    return x**2

log_msg("Defined foo")

if __name__ == '__main__':
    log_msg("__name__ == '__main__'")

    pool = Pool(2)
    log_msg("pool created")
    pows = pool.map(foo, range(10))
    log_msg("map completed")
    print pows
    log_msg("output printed")

log_msg("Finished running")

Example output for me:

tom@fannybawz:~$ ./multiproc.py
[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]
tom@fannybawz:~$ cat example.log 
INFO:root:22238: Started process
INFO:root:22238: Defined foo
INFO:root:22238: __name__ == '__main__'
INFO:root:22238: pool created
INFO:root:22240: {}: running foo
INFO:root:22239: {}: running foo
INFO:root:22240: {}: running foo
INFO:root:22239: {}: running foo
INFO:root:22240: {}: running foo
INFO:root:22239: {}: running foo
INFO:root:22240: {}: running foo
INFO:root:22239: {}: running foo
INFO:root:22240: {}: running foo
INFO:root:22240: {}: running foo
INFO:root:22238: map completed
INFO:root:22238: output printed
INFO:root:22238: Finished running
tom@fannybawz:~$ 

Try the same thing yourself with the Process version.