Popen.communicate()引发OSError:"[Errno 10] No child process". [英] Popen.communicate() throws OSError: "[Errno 10] No child processes"

问题描述

我正在尝试启动一个子进程，并使用subprocess模块​​从Python在Linux上获取其输出:

I'm trying to start up a child process and get its output on Linux from Python using the subprocess module:

#!/usr/bin/python2.4
import subprocess

p = subprocess.Popen(['ls', '-l', '/etc'],
                   stdout=subprocess.PIPE,
                   stderr=subprocess.PIPE)
out, err = p.communicate()

但是，我感到有些aki弱:有时，p.communicate()会抛出

However, I experience some flakiness: sometimes, p.communicate() would throw

OSError: [Errno 10] No child processes

什么会导致此异常?这里是否有任何不确定性或种族条件会导致脆弱?

What can cause this exception? Is there any non-determinism or race condition here that can cause flakiness?

推荐答案

您是否在脚本中拦截了SIGCHLD?如果您是Popen，则Popen将无法按预期运行，因为它依赖于它自己的信号处理程序.

Are you intercepting SIGCHLD in the script? If you are then Popen will not run as expected since it relies on it's own handler for that signal.

您可以通过注释掉Popen调用然后运行来检查SIGCHLD处理程序:

You can check for SIGCHLD handlers by commenting out the Popen call and then running:

strace python <your_script.py> | grep SIGCHLD

如果您看到类似的内容:

if you see something similar to:

rt_sigaction(SIGCHLD, ...)

然后，您遇到了麻烦.您需要在调用Popen之前禁用处理程序，然后在通信完成后将其重置(这可能会引起竞争状况，因此请当心).

then, you are in trouble. You need to disable the handler prior to calling Popen and then resetting it after communicate is done (this might introduce a race conditions so beware).

signal.signal(SIGCHLD, handler)
...
signal.signal(SIGCHLD, signal.SIG_DFL)
'''
now you can go wild with Popen. 
WARNING!!! during this time no signals will be delivered to handler
'''
...
signal.signal(SIGCHLD, handler)

据报道有一个python bug，据我所知尚未解决:

There is a python bug reported on this and as far as I see it hasn't been resolved yet:

http://bugs.python.org/issue9127

希望有帮助.

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