无需在python中收获僵尸进程吗？

Question

It seems to me in Python, there is no need to reap zombie processes.

For example, in the following code

    import multiprocessing
    import time

    def func(msg):
        time.sleep(2)
        print "done " + str(msg)

    if __name__ == "__main__":
        for i in range(10):
            p = multiprocessing.Process(target=func, args=('3'))
            p.start()
            print "child"+str(i)
        print "parent"
        time.sleep(100)

When all the child process exit, the parent process is still running and at this time, I checked the process using ps -ef and I noticed there is no defunct process.

Does this mean that in Python, there is no need to reap zombie process?

Answer 1

Those processes are not actually zombies since they should terminate successfully. You could set the child processes to be deamonic so they'll terminate if the main process terminates.

Answer 2

After having a look to the library - especially to multiprocessing/process.py -, I see that

1. in Process.start() , there is a _current_process._children.add(self) which adds the started process to a list/set/whatever,
2. a few lines above, there is a _cleanup() which polls and discards terminated processes, removing zombies.

But that doesn't explain why your code doesn't produce zombies, as the childs wait a while befor terminating, so that the parent's start() calls don't notice that yet.