多处理代码在导入时起作用，在被调用时中断 [英] Multiprocessing code works upon import, breaks upon being called

问题描述

在名为 test.py 的文件中，我有

print 'i am cow'
import multi4
print 'i am cowboy'

并在 multi4.py 我有

import multiprocessing as mp
manager = mp.Manager()
print manager

我很困惑的方式这段代码运作。

I am confused by the way this code operates.

在命令行中，如果我输入 python ，然后在python环境中键入 import test.py 我得到了预期的行为：

At the command line, if I type python and then in the python environment if I type import test.py I get the expected behavior:

Python 2.7.3 (default, Apr 10 2012, 23:31:26) [MSC v.1500 32 bit (Intel)] on win32 Type "help", "copyright", "credits" or "license" for more information.

>>>import test
i am cow
<multiprocessing.managers.SyncManager object at 0x025209B0>
i am cowboy 
>>>

但是如果我输入 test.py at命令行，我得到了

However if I type test.py at the command line, I get

i am cow
i am cow
i am cow
i am cow
i am cow
i am cow
i am cow
i am cow
i am cow
i am cow
i am cow
i am cow
i am cow
i am cow
i am cow
i am cow
i am cow
i am cow

除非我杀了它，否则大概会继续下去。当我杀了它时，我得到了一堆重复的错误：

Which would presumably go on forever unless I kill it. When I kill it, I get a bunch of repeated errors:

KeyboardInterrupt
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "C:\Python27\lib\multiprocessing\forking.py", line 373, in main
    prepare(preparation_data)
  File "C:\Python27\lib\multiprocessing\forking.py", line 488, in prepare
    '__parents_main__', file, path_name, etc
KeyboardInterrupt
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "C:\Python27\lib\multiprocessing\forking.py", line 373, in main
    prepare(preparation_data)
  File "C:\Python27\lib\multiprocessing\forking.py", line 488, in prepare
    '__parents_main__', file, path_name, etc
KeyboardInterrupt

那是怎么回事？为什么它在导入时表现一种方式，另一种在我尝试运行时呢？

So what is going on? Why does it behave one way under import, and another when I try to run it?

推荐答案

多处理 将无法正常工作，因为它无法正常运行在它生成的子进程中重新导入 __ main __ 。然而，实际上实际上帮助你，因为它保持 manager = mp.Manager（）行在子进程中递归执行当 Manager 启动时产生。

multiprocessing won't work properly in the interactive prompt on Windows, because it can't properly re-import __main__ in the child processes it spawns. However, that actually actually helps you here, since it keeps the manager = mp.Manager() line from being recursively executed in the child process that spawns when the Manager starts up.

但是在实际的脚本中，孩子可以重新导入 __ main __ 正确。您正在看到无限递归，因为如果__name__ ==__ main__，您不会使用保护对 mp.Manager（）的调用： guard，在Windows上需要到阻止 mp.Manager（）在重新导入时在子代中执行：

In the actual script, however, the child can re-import __main__ properly. You're seeing the infinite recursion because you're not protecting the call to mp.Manager() with an if __name__ == "__main__": guard, which is required on Windows to prevent mp.Manager() from being executed in the child when the re-import occurs:

import multiprocessing as mp
if __name__ == "__main__":
    manager = mp.Manager()
    print manager

编辑：

您的示例，您的主要脚本（ test.py）导入创建 Manager 的模块，需要一些重构。您需要通过调用实际使用 multiprocessing 的模块中的方法，从主脚本实例化 Manager ：

Your example, where your main script (test.py) imports the module that creates the Manager, needs a bit of refactoring. You need to instantiate the Manager from the main script, by calling a method in the module that actually uses multiprocessing:

print 'i am cow'
import multi4
if __name__ == "__main__":
    multi4.init_manager()
print 'i am cowboy'

multi4。 py

import multiprocessing as mp
manager = None
def init_manager():
    global manager
    manager = mp.Manager()

这是唯一的方法确保在实际执行脚本时只创建 Manager 。

This is the only way to make sure you only create the Manager when you're actually executing a script.

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