test_asyncio: SubprocessPidfdWatcherTests..test_close_dont_kill_finished() leaks a file descriptor

[vstinner]

BPO	38982
Nosy	@vstinner, @asvetlov, @1st1, @pablogsal
PRs	bpo-38982: Fix asyncio PidfdChildWatcher on waitpid() error #17477

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GitHub fields:

assignee = None
closed_at = <Date 2019-12-06.17:36:33.807>
created_at = <Date 2019-12-05.17:09:01.917>
labels = ['tests', '3.9', 'expert-asyncio']
title = 'test_asyncio: SubprocessPidfdWatcherTests..test_close_dont_kill_finished() leaks a file descriptor'
updated_at = <Date 2019-12-06.17:36:33.803>
user = 'https://github.com/vstinner'

bugs.python.org fields:

activity = <Date 2019-12-06.17:36:33.803>
actor = 'vstinner'
assignee = 'none'
closed = True
closed_date = <Date 2019-12-06.17:36:33.807>
closer = 'vstinner'
components = ['Tests', 'asyncio']
creation = <Date 2019-12-05.17:09:01.917>
creator = 'vstinner'
dependencies = []
files = []
hgrepos = []
issue_num = 38982
keywords = ['patch']
message_count = 5.0
messages = ['357869', '357871', '357873', '357919', '357928']
nosy_count = 4.0
nosy_names = ['vstinner', 'asvetlov', 'yselivanov', 'pablogsal']
pr_nums = ['17477']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue38982'
versions = ['Python 3.9']

[vstinner]

See on AMD64 Fedora Rawhide Refleaks 3.x:
https://buildbot.python.org/all/#/builders/82/builds/7

I found the leaking test using test.bisect_cmd:

$ ./python -m test test_asyncio -R 3:3 --fail-env-changed -v -m test.test_asyncio.test_subprocess.SubprocessPidfdWatcherTests.test_close_dont_kill_finished
...
test_asyncio leaked [1, 1, 1] file descriptors, sum=3

[vstinner]

Attached PR 17477 fix the leak.

PidfdChildWatcher was added to asyncio by bpo-38692:

commit 3ccdd9b
Author: Benjamin Peterson <benjamin@python.org>
Date: Wed Nov 13 19:08:50 2019 -0800

closes bpo-38692: Add a pidfd child process watcher to asyncio. (GH-17069)

[vstinner]

The test only fails on the Fedora Rawhide buildbot, likely because other Linux Refleak buildbots are using a kernel or libc without pidfd_open() ;-)

[vstinner]

New changeset e76ee1a by Victor Stinner in branch 'master':
bpo-38982: Fix asyncio PidfdChildWatcher on waitpid() error (GH-17477)
e76ee1a

[vstinner]

I manually validated that my change fixed the test_asyncio leak:

$ ./python -m test test_asyncio -R 3:3 --fail-env-changed -v -m test_subprocess
(...)
Tests result: SUCCESS

I close the issue. Thanks Pablo for the review ;-)