subprocess.poll() does not handle errno.ECHILD "No child processes"

[twhitema]

BPO	15756
Nosy	@gpshead, @jcea
Files	issue15756_poll_v1.patch

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/gpshead'
closed_at = <Date 2012-09-29.19:03:53.624>
created_at = <Date 2012-08-21.19:15:16.936>
labels = ['type-bug', 'library']
title = 'subprocess.poll() does not handle errno.ECHILD "No child processes"'
updated_at = <Date 2012-09-29.19:03:53.623>
user = 'https://bugs.python.org/twhitema'

bugs.python.org fields:

activity = <Date 2012-09-29.19:03:53.623>
actor = 'gregory.p.smith'
assignee = 'gregory.p.smith'
closed = True
closed_date = <Date 2012-09-29.19:03:53.624>
closer = 'gregory.p.smith'
components = ['Library (Lib)']
creation = <Date 2012-08-21.19:15:16.936>
creator = 'twhitema'
dependencies = []
files = ['26951']
hgrepos = []
issue_num = 15756
keywords = ['patch']
message_count = 5.0
messages = ['168798', '168799', '169581', '171588', '171589']
nosy_count = 5.0
nosy_names = ['gregory.p.smith', 'jcea', 'twhitema', 'tshepang', 'python-dev']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = None
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue15756'
versions = ['Python 2.7', 'Python 3.2', 'Python 3.3', 'Python 3.4']

[twhitema]

In the case of a "errno.ECHILD" exception - Python's subprocess module misses the fact that the process has already ended.

The following code will wait indefinitely, even though the launched process is quickly ended:

import subprocess, signal
signal.signal(signal.SIGCLD, signal.SIG_IGN)
p = subprocess.Popen(['echo','foo'])
while p.poll() is None:
   pass # wait for the process to exit

Note: This is the exact same issue as bpo-1731717, but applying to the subprocess.poll() method instead of the subprocess.wait() method.

[twhitema]

The attached patch handles errno.ECHILD in the _internal_poll() method and I've updated the existing "sigchild_ignore.py" test file to perform polling as well.

An unpatched version of Pyhton would normally hang on this particular test, whilst the patched version will run successfully.

[gpshead]

thanks! I'll take care of getting this fix in.

[python-dev]

New changeset 484c50bf445c by Gregory P. Smith in branch '3.2':
Fixes issue bpo-15756: subprocess.poll() now properly handles errno.ECHILD
http://hg.python.org/cpython/rev/484c50bf445c

New changeset ba8d85552e34 by Gregory P. Smith in branch '3.3':
Fixes issue bpo-15756: subprocess.poll() now properly handles errno.ECHILD
http://hg.python.org/cpython/rev/ba8d85552e34

New changeset 9032b3f52819 by Gregory P. Smith in branch 'default':
Fixes issue bpo-15756: subprocess.poll() now properly handles errno.ECHILD to
http://hg.python.org/cpython/rev/9032b3f52819

[python-dev]

New changeset 53e91fa35f8e by Gregory P. Smith in branch '2.7':
Issue bpo-15756: subprocess.poll() now properly handles errno.ECHILD to
http://hg.python.org/cpython/rev/53e91fa35f8e