[issue17131] subprocess.Popen.terminate can raise exception on Posix

[Gregory P. Smith]

Changes by Gregory P. Smith :


--
resolution:  -> duplicate
status: open -> closed
superseder:  -> subprocess.Popen.send_signal doesn't check whether the process 
has terminated

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[issue17131] subprocess.Popen.terminate can raise exception on Posix

[Martin Panter]

Martin Panter added the comment:

This is more or less a dupe of Issue 6973, which also has a potential patch.

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[issue17131] subprocess.Popen.terminate can raise exception on Posix

[Gregory P. Smith]

Gregory P. Smith added the comment:

agreed, we could at least do that for the Popen methods.

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[issue17131] subprocess.Popen.terminate can raise exception on Posix

[Gregory P. Smith]

Changes by Gregory P. Smith g...@krypto.org:


--
assignee:  - gregory.p.smith
stage:  - needs patch

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[issue17131] subprocess.Popen.terminate can raise exception on Posix

[Martin Panter]

Martin Panter added the comment:

For Posix (dunno about Windows), calling terminate or kill at the OS level 
after a poll or wait has already succeeded is a bad idea, because the PID may 
have been recycled. It is essentially operating on a released resource, similar 
to calling “os.close” on a closed FD, or freeing unallocated memory.

There is a way to know if the PID is still valid though. Just make sure that 
successful poll and wait calls invalidate the PID. Then calling terminate or 
kill, or any other operation that requires the PID, would no longer be valid 
(or could do nothing if that is more appropriate). Similar to the behaviour of 
file objects after they are closed: subsequent close calls do nothing; other 
operations raise an exception.

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[issue17131] subprocess.Popen.terminate can raise exception on Posix

[Gregory P. Smith]

Gregory P. Smith added the comment:

issue14252 appears to have been a fix for the windows side only.

On Posix the best that could be done here is to catch OSError within 
Popen.terminate() and Popen.kill() and ignore the problem if there was an error.

We do not have a way to know if the child process exists any longer or even to 
know if the process with the PID this call is sending the signal to is this 
Popen instances' child process or if the PID has already been recycled by the 
OS and used by another unfortunate process.

the bigger question is... should we.  this seems like an API change rather than 
a bugfix so I'm more inclined to do this in 2.5 only in case someone was 
relying on the exception to tell them that the process had already died.

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[issue17131] subprocess.Popen.terminate can raise exception on Posix

[Mark Lawrence]

Mark Lawrence added the comment:

@Siona sorry about the delay in getting back to you.  Can someone try this 
please as I've only got Windows.

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nosy: +BreamoreBoy
versions: +Python 3.4, Python 3.5 -Python 2.6, Python 3.2

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[issue17131] subprocess.Popen.terminate can raise exception on Posix

[Ned Deily]

Changes by Ned Deily n...@acm.org:


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nosy: +gregory.p.smith

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[issue17131] subprocess.Popen.terminate can raise exception on Posix

[S Arrowsmith]

New submission from S Arrowsmith:

Compare this with the script in #14252:

p = Popen(['/bin/sleep', '1'])
time.sleep(1)
p.terminate()
print p.poll()
p.terminate()

Output is:

0
Traceback (most recent call last):
  File stdin, line 1, in module
  File /usr/lib/python2.6/subprocess.py, line 1269, in terminate
self.send_signal(signal.SIGTERM)
  File /usr/lib/python2.6/subprocess.py, line 1264, in send_signal
os.kill(self.pid, sig)
OSError: [Errno 3] No such process

The 0 return from poll() indicates that the subprocess ran to completion, 
rather than being terminated by the first terminate. So the first terminate 
does nothing, but the second terminate raises an exception. In 
http://bugs.python.org/issue14252#msg155396 :

Raising an exception on terminate is a bug.

--
components: Library (Lib)
messages: 181425
nosy: siona
priority: normal
severity: normal
status: open
title: subprocess.Popen.terminate can raise exception on Posix
type: behavior
versions: Python 2.6, Python 2.7, Python 3.2

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