Why do these two processes behave like this?

Question

I'm creating two instances of a process over here but when I'm running this program I'm getting only main function output.

import multiprocessing
import time

def sleepy_man():
    print("Starting to Sleep")
    time.sleep(1)
    print("Done Sleeping")

tic = time.time()
p1 = multiprocessing.Process(target=sleepy_man)
p2 = multiprocessing.Process(target=sleepy_man)
p1.start()
p2.start()

toc = time.time()

print("Done in {:.4f} seconds".format(toc-tic))

Output

Done in 0.0554 seconds

I was doing it for practice from this blog only. Source: https://www.analyticsvidhya.com/blog/2021/04/a-beginners-guide-to-multi-processing-in-python/

Answer 1

It is worth noting you would see the same behavior if you had somehow set p1.daemon = p2.daemon = True.

It is also possibly due to output buffering, rather than logic errors. Two questions:

• If you add a sys.stdout.flush() or flush=True to your print, do you see different behavior?
• If you run this with time python foobar.py does it take .02s or 1s to run?

Obviously, continuing your tutorial and correctly adding .join() below will resolve the issue in a way that would be expected for normal usage.