Multiprocess Python: Working code of a tutorial doesn't work when I try it

Question

I am watching the tutorial https://www.youtube.com/watch?v=fKl2JW_qrso (shown at 8.18 min) about multiprocessing. I am running the code copied from there:

import multiprocessing
import time
import os

start = time.perf_counter()


def do_something():

    print("sleeping 1 sec...")
    time.sleep(1)

    print("done sleeping...")


p1 = multiprocessing.Process(target=do_something)
p2 = multiprocessing.Process(target=do_something)

p1.start()
p2.start()

finish = time.perf_counter()

print("finished in " + str(round((finish-start),2))   + " seconds(s)")

os.system("pause")

But when I run it on my computer I have the following error message (but the same code works on the tutorial):

An attempt has been made to start a new process before the current process has finished its bootstrapping phase. This probably means that you are not using fork to start your child processes and you have forgotten to use the proper idiom in the main module: if name == 'main': freeze_support() ... The "freeze_support()" line can be omitted if the program is not going to be frozen to produce an executable.

https://stackoverflow.com/questions/18204782/runtimeerror-on-windows-trying-python-multiprocessing — Inder, May 30 '20 at 16:10
you need a if __name__=='__main__': block where you call the multiprocessing — Luv, May 30 '20 at 16:10
can it be because running it in a windows machine is different? — blu potatos, May 30 '20 at 16:19
The code works fine in python3. You better try to join the new processes at the end with `p1.join(); p2.join()` — hesham_EE, May 30 '20 at 16:19

score 0 · Answer 1 · edited May 30 '20 at 16:38

Thanks for all your comments. Finally it works. So basically in windows it needs to be written in a slightly different way:

import multiprocessing
import time
import os

start = time.perf_counter()


def do_something():

    print("sleeping 1 sec...")
    time.sleep(1)

    print("done sleeping...")

if  __name__ == "__main__":
    p1 = multiprocessing.Process(target=do_something)
    p2 = multiprocessing.Process(target=do_something)

    p1.start()
    p2.start()

    p1.join()
    p2.join()

    finish = time.perf_counter()

    print("finished in " + str(round((finish-start),2))   + " seconds(s)")

    os.system("pause")

Multiprocess Python: Working code of a tutorial doesn't work when I try it

1 Answers1