Why is multiprocessing.Process not running in parallel?

AAB07 0
Viewed 9

I have been playing with multiprocessing, and I am trying to understand how it works and how to run code in parallel. For this, I created the following very trivial script:

import multiprocessing

import time


def write_something(text="Hi mum!", duration=60, interval=1):
    time_end = time.time() + duration
    while time.time() < time_end:
        time.sleep(interval)
        print(text)


def multiprocessing_process():
    process1 = multiprocessing.Process(target=write_something(text="Hi mum!", duration=20, interval=10))
    process2 = multiprocessing.Process(target=write_something(text="Hi dad!", duration=20, interval=5))
    process1.start()
    process2.start()
    process1.join()
    process2.join()


def main():
    multiprocessing_process()
    #multiprocessing_pool()


# Press the green button in the gutter to run the script.
if __name__ == '__main__':
    main()

Based on what I've been reading, I was expecting the code to run on parallel, but the console output was:

Hi mum!
Hi mum!
Hi dad!
Hi dad!
Hi dad!
Hi dad!

While I was expecting something more like this:

Hi dad!
Hi dad!
Hi mum!
Hi dad!
Hi mum!
Hi dad!

I managed to observe this result by using multiprocessing.Pool and async_apply. But I don't understand why it doesn't work that way with multiprocessing.Process. I thought it was supposed to created 2 processes that run independently. What am I missing?

python-multiprocessing python-3.x python
1 Answers

In case you don't fully understand the answer in the duplicate link, here's how to fix your code:

import multiprocessing, time

def write_something(text="Hi mum!", duration=60, interval=1):
    time_end = time.time() + duration
    while time.time() < time_end:
        time.sleep(interval)
        print(text)

def multiprocessing_process():
    process1 = multiprocessing.Process(target=write_something, args=("Hi mum!", 20, 10))
    process2 = multiprocessing.Process(target=write_something, args=("Hi dad!", 20, 5))
    process1.start()
    process2.start()
    process1.join()
    process2.join()

def main():
    multiprocessing_process()
    #multiprocessing_pool()

# Press the green button in the gutter to run the script.
if __name__ == '__main__':
    main()

Result:

Hi dad!
Hi mum!
Hi dad!
Hi dad!
Hi mum!
Hi dad!
user567000
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