Python multiprocessing debug

Question

I'm trying to get the hang of Python multiprocessing but my tests so far show sequential running instead of parallelism.

I tried this simple code:

multiprocessing.py:

import multiprocessing
import os


def proc1():
    os.system('python proc1.py')

def proc2():
    os.system('python proc2.py')

if __name__ == "__main__":
    p1 = multiprocessing.Process(target=proc1())
    p2 = multiprocessing.Process(target=proc2())
    p1.start()
    p2.start()

proc1.py:

import time
for i in range(0,5):
    print('process 1: ', i)
    time.sleep(0.5)

proc2.py:

import time
for i in range(0,5):
    print('process 2: ', i)
    time.sleep(0.5)

My understanding is that this should run parallel on different CPUs, however, the console output is always this:

process 1:  0
process 1:  1
process 1:  2
process 1:  3
process 1:  4
process 2:  0
process 2:  1
process 2:  2
process 2:  3
process 2:  4

Process finished with exit code 0

I think the two process outputs should be mixed and in varying order, depending on which core is 'faster'. Is this a limitation of Pycharm? Or am I doing something wrong?

Eddoasso · Accepted Answer · 2021-08-29 15:52:41Z

2

It's a simple error in syntax. By doing

p1 = multiprocessing.Process(target=proc1())

you are saying that the target should be the output from proc1. What you want is

p1 = multiprocessing.Process(target=proc1)

That way the target is the function proc1

answered Aug 29, 2021 at 15:52

Eddoasso

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