New submission from Daniel Shaulov:
Basically -
subprocess.check_output("ping localhost", shell=True, timeout=5)
Will hang forever.
What happens is that subprocess.run times out on communicate, sends SIGKILL *to
the shell* and then calls communicate again without the timeout. But nothing
actually closes the "ping" command so the second communicate will never exit.
Even if we put a timeout on the second communicate, it won't be good enough
because that "ping" will still be "leaked".
This SO question is about the fact that kill doesn't work when shell=True, and
might be relevant for this issue:
http://stackoverflow.com/questions/4789837/how-to-terminate-a-python-subprocess-launched-with-shell-true
As a possible fix I propose doing the following:
1. Add killpg to the Popen class.
2. Add an argument to run - "kill_group" that makes run use killpg instead of
kill
3. Users can all:
subprocess.check_output("ping localhost", shell=True, start_new_session=True,
kill_group=True, timeout=5)
And have it work fine. This is the best I could come up with, without breaking
any existing behavior.
Other options to consider:
1. Not have kill_group argument and to implicitly kill by group when
start_new_session is True (but this is not really backwards compatible).
2. Having kill_group as an argument for Popen and not run, and when kill is
called, it will call killpg if the option was specified.
A patch is attached with my proposed solution.
----------
components: Library (Lib)
files: killpg.patch
keywords: patch
messages: 261533
nosy: Daniel Shaulov, astrand
priority: normal
severity: normal
status: open
title: subprocess.check_output with shell=True ignores the timeout
type: behavior
versions: Python 3.5, Python 3.6
Added file: http://bugs.python.org/file42122/killpg.patch
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<http://bugs.python.org/issue26534>
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