multiprocessing difference between Linux and Windows

[direl]

I was trying to accept timed input when I noticed that Windows did not behave as I expected. A simplified version of the code to demonstrate this is below:

import multiprocessing, sys, os

def _input_with_timeout_process(stdin_file_descriptor, queue, prompt):
    sys.stdin = os.fdopen(stdin_file_descriptor)
    queue.put(input(prompt))
    return

print("=== 1 ===", 'parent process:', os.getppid(), 'my pid:', os.getpid())

if __name__ == '__main__':
    queue = multiprocessing.Queue()
    process = multiprocessing.Process(target=_input_with_timeout_process, 
        args=(sys.stdin.fileno(), queue, "Say something: "))
    process.start()
    try:
        process.join(10)
        if process.is_alive():
            raise ValueError("Timed out waiting for input.")
        print("I saw:", queue.get())
    except ValueError:
        print("Sorry, too slow.")
    finally:
        process.terminate()

Running this with Python 3.8.2 on Ubuntu 20.04 gives:

Output:
direl@MD-3670:~/Shared$ python min_mp_test.py
=== 1 === parent process: 30833 my pid: 32234
Say something: g
I saw: g
direl@MD-3670:~/Shared$

However on Windows 10 with Python 3.8.6 I get

Output:
PS C:\Users\mdavi\Documents> python z:min_mp_test.py
=== 1 === parent process: 4288 my pid: 5408
=== 1 === parent process: 5408 my pid: 5764
Say something: f
I saw: f
PS C:\Users\mdavi\Documents>

It looks as though the second process is escaping from its function definition and executing any subsequent code that is not in either a function definition or an
if __name__ == '__main__': statement.

While making sure that everything is indented under something will avoid the problem I was curious if this is actually the correct or even accepted behaviour. Note that the original program did not have the if __name__ == '__main__': and its behaviour was a lot stranger.