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Avoiding defunct processes

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  Avoiding defunct processes Richard <richardbp@gmail.com> - 2012-11-01 19:16 -0700
    Re: Avoiding defunct processes Chris Angelico <rosuav@gmail.com> - 2012-11-02 13:36 +1100
    Re: Avoiding defunct processes Nobody <nobody@nowhere.com> - 2012-11-02 15:46 +0000

#32590 — Avoiding defunct processes

Hello,

I create child processes with subprocess.Popen().
Then I either wait for them to finish or kill them.
Either way these processes end up as defunct until the parent process
completes:
$ ps e
6851 pts/5    Z+     1:29 [python] <defunct>

This confuses another library as to whether the processes are
complete.
For now I detect which processes are defunct by parsing the output of
"ps".
What would you recommend? I am hoping there is a cleaner way.

Richard

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#32591

On Fri, Nov 2, 2012 at 1:16 PM, Richard <richardbp@gmail.com> wrote:
> Hello,
>
> I create child processes with subprocess.Popen().
> Then I either wait for them to finish or kill them.
> Either way these processes end up as defunct until the parent process
> completes:
> $ ps e
> 6851 pts/5    Z+     1:29 [python] <defunct>
>
> This confuses another library as to whether the processes are
> complete.
> For now I detect which processes are defunct by parsing the output of
> "ps".
> What would you recommend? I am hoping there is a cleaner way.

That's a zombie process, it's finished but the parent hasn't wait()ed
for it yet.

http://docs.python.org/3.3/library/subprocess.html#subprocess.Popen.wait

Once the process has ended, call that to get its return value and
clean everything up.

ChrisA

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#32635

On Thu, 01 Nov 2012 19:16:17 -0700, Richard wrote:

> I create child processes with subprocess.Popen().
> Then I either wait for them to finish or kill them.
> Either way these processes end up as defunct until the parent process
> completes:
> $ ps e
> 6851 pts/5    Z+     1:29 [python] <defunct>

You need to either call the .wait() method, or keep calling the .poll()
method until the .returncode attribute is not None.

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