Python process blocking main thread

Question

I can't figure out why a Python process would block the main thread. An example:

import multiprocessing
import time


def do_something(name: str):
    while True:
        print(name)


if __name__ == '__main__':
    p1 = multiprocessing.Process(target=do_something, args=(1,))
    p1.start()

    p2 = multiprocessing.Process(target=do_something, args=(2,))
    p2.start()

    while True:
        print(3)
        time.sleep(.1)

The output result of this is a whole bunch of 1 and 2's. While 3 (main process/thread) is never printed. When I remove the time.sleep it starts printing again. Why is it that a time.sleep can make Processes block the main thread?

Answer 1

如果将输出通过管道传输到文本文件，您会发现它确实打印了 3。但是，它大约每 100 毫秒打印一次，而其他两个进程连续打印，因此您可能在控制台中看不到它。