多处理事件不起作用 [英] Multiprocessing Event not Working

问题描述

我已经使用多处理模块在Python 3中编写了以下代码.更多如何使用Event是测试脚本.但是，它不起作用.

I have written the following code in Python 3 using the multiprocessing module. It's more of a test script to see how to use Event. However, it's not working.

import multiprocessing, time

from multiprocessing import Process, Event

event = Event()

def f(n):

    if n == 1:

        print("starting")

        event.wait()

        print("Done!")


    if n == 2:

        time.sleep(3)

        event.set()

        print("setting")

if __name__ == "__main__":

    p1 = Process(target = f, args = (1,))
    p2 = Process(target = f, args = (2,))

    p1.start()

    p2.start()

    time.sleep(1000)

但是，当我运行它时，我只会得到输出:

However, when I run this I only get the output:

starting
setting

我想获取输出:

starting
setting
Done!

但是由于某些原因，p2进程调用了event.set()之后，p1进程没有继续执行其代码.

But for some reason the p1 Process is not moving on with its code after event.set() has been called by the p2 process.

有任何想法为什么会发生这种情况?

Any ideas why this is happening?

推荐答案

来自

From the multiprocessing programming guidelines.

明确将资源传递给子进程

Explicitly pass resources to child processes

...最好将对象作为参数传递给子进程的构造函数.

... it is better to pass the object as an argument to the constructor for the child process.

除了使代码(可能)与Windows兼容...

Apart from making the code (potentially) compatible with Windows ...

在Windows上，您需要将共享对象传递到Process构造函数的参数列表.否则，子进程将获得一个全新的副本，而不是父进程的副本.这就是f(1)挂起，正在等待另一个Event对象的原因.

On Windows, you need to pass the shared objects to the Process constructor list of arguments. Otherwise, the child process will get a brand new copy instead of the parent's one. This is why f(1) hangs, it is waiting on another Event object.

只需更改这样的代码即可.

Just change the code like this.

def f(n, event):
    if n == 1:
        print("starting")
        event.wait()
        print("Done!")
    elif n == 2:
        time.sleep(3)
        event.set()
        print("setting")

if __name__ == "__main__":
    event = Event()  # one instance of Event only

    p1 = Process(target = f, args = (1, event))
    p2 = Process(target = f, args = (2, event))
    p1.start()
    p2.start()
    p1.join()
    p2.join()

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