getting the return value of a function used in multiprocess

Question

Say I have the below code, a function that does something, which is initiated in a Process, and returns a value.

from multiprocessing import Process

def my_func(arg):
    return 'Hello, ' + arg

p1 = Process(target=my_func, args=('John',)
p1.start()
p1.join()

How do I get the return value of the function?

Possible duplicate of [How can I recover the return value of a function passed to multiprocessing.Process?](https://stackoverflow.com/questions/10415028/how-can-i-recover-the-return-value-of-a-function-passed-to-multiprocessing-proce) — Jan Christoph Terasa, Feb 10 '19 at 10:40
This might help: https://docs.python.org/2/library/multiprocessing.html#exchanging-objects-between-processes — e.dan, Feb 10 '19 at 10:43

Ari · Accepted Answer · 2020-01-16T11:48:36.350

16

Answer

from multiprocessing import Process, Queue

Q = Queue()

def my_func(arg):
    Q.put('Hello, ' + arg)

p1 = Process(target=my_func, args=('John',))
p1.start()
print(Q.get())
p1.join()

edited Jan 16 '20 at 11:48

answered Aug 20 '19 at 23:04

Ari

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1

Please add the missing brackets: Queue(), Process(target=my_func, args=('John',)). – spaenigs Jan 09 '20 at 11:03
1

This implies to modify your original `my_func` adding Q if you want to use it parallel – leonard vertighel Dec 22 '21 at 23:18

score 0 · Answer 2 · answered Nov 10 '22 at 02:26

You can pass Queue of multiprocessing to my_func() as shown below:

from multiprocessing import Process, Queue

def my_func(arg, q):
    q.put('Hello, ' + arg)
    
queue = Queue()                            # Here
p1 = Process(target=my_func, args=('John', queue))
p1.start()
print(queue.get())
p1.join()

This is the result below:

Hello, John

Be careful, if using queue module below with process, the program doesn't work properly:

import queue
queue = queue.Queue()

So, just use Queue of multiprocessing module with process as I used in the code above:

from multiprocessing import Queue
queue = Queue()

getting the return value of a function used in multiprocess

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