为什么Python多处理守护进程不能打印到标准输出？

Question

我一直在尝试多处理,并使用守护进程运行到一个mindblock.

我有一个守护进程和一个非守护进程,守护进程每隔一秒无限期地发出输出,而非守护进程在启动时立即打印输出,休眠3秒,然后再次打印并返回.

问题是,守护进程的预期输出根本没有显示出来.

回顾过去关于守护进程的SO问题,常见问题似乎是在守护进程之前结束的其他进程,或者需要刷新以显示输出的stdout.两者都(我认为)已得到解决,但我仍然只看到来自非守护进程的打印输出.

代码:

from multiprocessing import Process, current_process
import sys
import time

def worker():
    """
    Announce that the process has started, sleep 3 seconds
    then announce that the process is ending.
    """
    name = current_process().name
    print name, 'starting...'
    sys.stdout.flush()

    time.sleep(3)
    print name, 'ending...'
    sys.stdout.flush()

    return


def daemon():
    """
    Announce that the process has started, beep, then beep
    once every second
    """
    name = current_process().name
    print name, 'starting...'
    print 'beep...'
    sys.stdout.flush()

    while True:
        time.sleep(1)
        print 'beep...'
        sys.stdout.flush()


if __name__=='__main__':
    d = Process(target=daemon)
    d.daemon = True
    d.start()

    p = Process(target=worker)
    p.daemon = False
    p.start()

预期产出:

Process-1 starting... # Order here may vary
beep...
Process-2 starting...
beep...
beep...
Process-2 ending... #There may or may not be another beep here

实际生产的内容:

Process-2 starting...
Process-2 ending...

任何关于为什么会发生这种情况的建议都会得到真正的体会

Answer 1

您可以通过放置打开日志来更清楚地了解事件的顺序

import multiprocessing as mp
logger = mp.log_to_stderr(logging.INFO)

在其他进口声明之后.然后你的程序将产生类似于:

[INFO/Process-1] child process calling self.run()
[INFO/MainProcess] process shutting down
Process-1 starting...
beep...
[INFO/Process-2] child process calling self.run()
[INFO/MainProcess] calling terminate() for daemon Process-1
Process-2 starting...
[INFO/MainProcess] calling join() for process Process-2
Process-2 ending...
[INFO/Process-2] process shutting down
[INFO/Process-2] process exiting with exitcode 0
[INFO/MainProcess] calling join() for process Process-1

因此,主要开始先关闭,然后终止进程-1,即守护进程.这就是为什么在Process-2继续时你不会再看到哔哔声的原因.