Python - load and use new process multiple times with different arguments

Question

I wanna create a seperate python process with loaded functions, which can be acessed/used/called later with different arguments multiple times (to overcome GIL). This is kind of like multiprocessing, but creating a new process via multiprocessing is too slow, because (as I understood) the process is unloaded after its execution. I'm not sure what exactly do I need to use.

How can I start a process multiple times with different args without a need to create it again?

I tried using multiprocessing, but I can't use it several times (AssertionError: cannot start a process twice). I also checked celery, but I'm not sure if this is the right way

Example:

from multiprocessing import Process


def add(a, b):
    print(a + b)


if __name__ == "__main__":
    p = Process(target=add, args=(5, 5))
    p.start()
    p.join()

    p.start()  # Error

Answer 1

You can create a separate Python script that loads the necessary functions and runs a loop to listen for incoming requests. Then communicate with this script from main process using a suitable interprocess communication mechanism such as pipes, sockets, or shared memory.

1. Create a separate worker.py script, which defines the functions you want to use and listens for incoming requests:

import multiprocessing as mp

def add(a, b):
    return a + b

def worker():
    while True:
        task, args = q.get()
        if task == 'add':
            result = foo(*args)
            q.put(result)
        else:
            break

if __name__ == '__main__':
    q = mp.Queue()
    p = mp.Process(target=worker)
    p.start()

2. In main process, you can communicate with the worker process by putting tasks and arguments onto the queue, and waiting for results to come back:

if __name__ == '__main__':
    q = mp.Queue()
    p = mp.Process(target=worker)
    p.start()

    q.put(('add', [5, 5]))  # Compute add(5, 5)
    result = q.get()    # Get the result (10)

    q.put(('add', [3, 3]))  # Compute bar(3, 3)
    result = q.get()    # Get the result (6)

    q.put(('stop', []))  # Stop the worker process
    p.join()