Shared array multiprocessing Python

Question

I am running a multi-process code in Python with a shared array. The problem is that I can't initialise that array...
To share an array in a multi-process program I have read I need to use multiprocessing.Array, but when I try it as in the code below it is not printing anything + I don't have error messages.

import multiprocessing
...
...

if  __name__ == "__main__":

   an_array= multiprocessing.Array("i", [1,2])

   print(an_array)       # why does it not print anything? I was expecting to print [1,2]

   p1 = multiprocessing.Process(target=function1, args = [an_array, 3]

Which python version are you using ? Also, i can't reproduce this behaviour and your code will not print [1, 2] but i'll print anothing thing. — Chiheb Nexus
– Chiheb Nexus, Commented May 31, 2020 at 0:01
After fixing the syntax errors your code prints <SynchronizedArray wrapper for <multiprocessing.sharedctypes.c_int_Array_2 object at 0x7f7bbc63df28>>. I am running Ubuntu. — tdelaney
– tdelaney, Commented May 31, 2020 at 16:40
Can you include your operating system and how you run this code (eg, command line, jupyter, etc...)? — tdelaney
– tdelaney, Commented May 31, 2020 at 16:42

Artiom Kozyrev · Accepted Answer · 2020-05-31 16:34:01Z

3

To print elements inside the Array do the following:

import multiprocessing

if __name__ == '__main__':

    an_array = multiprocessing.Array("i", [1, 2])

    # first choice to print element in Array:
    for element in an_array:
        print(element)

    # second choice to print elements in Array:
    print(an_array[:])

    # third choice to print elements in Array:
    print(list(an_array[:]))

answered May 31, 2020 at 16:34

Artiom Kozyrev

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