问题描述

我不明白为什么这么简单的代码

I don't understand why this simple code

# file: mp.py
from multiprocessing import Process
import sys

def func(x):
    print 'works ', x + 2
    sys.stdout.flush()

p = Process(target= func, args= (2, ))
p.start()
p.join()
p.terminate()
print 'done'
sys.stdout.flush()

连续创建pythonw.exe"进程并且它不打印任何东西，即使我从命令行运行它:

creates "pythonw.exe" processes continuously and it doesn't print anything, even though I run it from the command line:

python mp.py

我在 32 位和 64 位的 Windows 7 上运行最新的 Python 2.6

I am running the latest of Python 2.6 on Windows 7 both 32 and 64 bits

推荐答案

你需要保护然后使用 if __name__ == '__main__': 进入程序的入口点.

You need to protect then entry point of the program by using if __name__ == '__main__':.

这是一个特定于 Windows 的问题.在 Windows 上，您的模块必须导入新的 Python 解释器才能访问您的目标代码.如果你不停止这个新的解释器运行启动代码，它将产生另一个孩子，然后再产生另一个孩子，直到它的 pythonw.exe 进程一目了然.

This is a Windows specific problem. On Windows your module has to be imported into a new Python interpreter in order for it to access your target code. If you don't stop this new interpreter running the start up code it will spawn another child, which will then spawn another child, until it's pythonw.exe processes as far as the eye can see.

其他平台使用os.fork() 启动子进程，所以不存在重新导入模块的问题.

Other platforms use os.fork() to launch the subprocesses so don't have the problem of reimporting the module.

所以您的代码需要如下所示:

So your code will need to look like this:

from multiprocessing import Process
import sys

def func(x):
    print 'works ', x + 2
    sys.stdout.flush()

if __name__ == '__main__':
    p = Process(target= func, args= (2, ))
    p.start()
    p.join()
    p.terminate()
    print 'done'
    sys.stdout.flush()

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