Question

kill subprocess when python process is killed?

Asked by: mweber02

I am writing a python program that lauches a subprocess (using Popen).
I am reading stdout of the subprocess, doing some filtering, and writing to
stdout of main process.
When I kill the main process (cntl-C) the subprocess keeps running.
How do I kill the subprocess too? The subprocess is likey to run a long time.

Context:
I'm launching only one subprocess at a time, I'm filtering its stdout.
The user might decide to interrupt to try something else.

I'm new to python; solution must be for Python 2.5 (windows) to help me.

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Asked On
2009-08-06 at 12:50:22ID24632821
Tags

python

,

windows

Topic

Python Scripting Language

Participating Experts
2
Points
500
Comments
5

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Answers

 

by: HonorGodPosted on 2009-08-06 at 17:09:27ID: 25039131

One possible solution:
- when child process is created, create a "watcher" process that know the processID of the child process, and the parent process.
- if the the parent process finished (e.g., is killed), then it can use the saved child process ID to kill it.

 

by: peprPosted on 2009-08-06 at 23:56:30ID: 25040385

I believe that signals are not available in Windows. This way, the signal module is not that much usefull. However, you can still catch the KeyboardInterrupt exception when Ctrl-C is pressed.

Now, it depends on what Python version you use to terminate the child. It should be easier with Python 2.6 -- see the snippet below. See the http://code.activestate.com/recipes/347462/ recipe on how to kill the process in Windows. Basically, you need to use win32api module or ctypes. The ctypes is the standard module from Python 2.5.

import subprocess
 
 
try:
    child = subprocess.Popen(...you know what to put here...)
    child.wait()   # wait for the child to terminate
    
except KeyboardInterrupt:   # when Ctrl-C is pressed
    child.terminate()       # new in Python 2.6
    # or you have to use an alternative way of killing the existing process.
    # You can use child.pid to get PID of the process.

                                              
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by: peprPosted on 2009-08-07 at 00:01:02ID: 25040399

Well, I have just noticed you want Python 2.5.

Warning, I did not tested the termination of a process. Please, post here if it works.

import ctypes
import subprocess
 
 
try:
    child = subprocess.Popen(...you know what to put here)
    child.wait()   # wait for the child to terminate
    
except KeyboardInterrupt:   # when Ctrl-C is pressed
    # Copied from recipe http://code.activestate.com/recipes/347462/
    PROCESS_TERMINATE = 1
    handle = ctypes.windll.kernel32.OpenProcess(PROCESS_TERMINATE, False, child.pid)
    ctypes.windll.kernel32.TerminateProcess(handle, -1)
    ctypes.windll.kernel32.CloseHandle(handle)

                                              
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by: mweber02Posted on 2009-08-10 at 11:45:09ID: 31613869

The suggested solution worked.

I ended up needing a bit more, because I wanted all children of the subprocess to be killed too. I ended up using the windows command TASKKILL, which has an option to kill all subprocesses.

An alternative to using the try/except (for my application, anyway) is to use the atexit module, so that a cleanup routine will be called when exiting (either by normal termination or cntl-C).

 

by: peprPosted on 2009-08-11 at 00:22:25ID: 25066755

Thanks for the points and for sharing your additional experience ;)

20120131-EE-VQP-002

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