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gh-151179: Fix pidfd leak in asyncio _PidfdChildWatcher #151186

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gh-151179: Fix pidfd leak in asyncio _PidfdChildWatcher #151186

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6bf7e17
gh-151179: Fix pidfd leak in asyncio _PidfdChildWatcher
deadlovelll Jun 9, 2026
de43735
removed class: from news
deadlovelll Jun 9, 2026
d765491
Use try/finally instead of a nested handler
deadlovelll Jun 10, 2026
0eab9be
Rewrite test to use the real watcher path
deadlovelll Jun 10, 2026
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4 changes: 2 additions & 2 deletions Lib/asyncio/unix_events.py
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Original file line number Diff line number Diff line change
Expand Up @@ -887,8 +887,8 @@ def _do_wait(self, pid, pidfd, callback, args):
pid)
else:
returncode = waitstatus_to_exitcode(status)

os.close(pidfd)
finally:
os.close(pidfd)
callback(pid, returncode, *args)

class _ThreadedChildWatcher:
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40 changes: 40 additions & 0 deletions Lib/test/test_asyncio/test_unix_events.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1333,5 +1333,45 @@ async def child_main():

self.assertEqual(result.value, 0)


@unittest.skipUnless(
unix_events.can_use_pidfd(),
"operating system does not support pidfd",
)
class PidfdChildWatcherTests(test_utils.TestCase):

def setUp(self):
super().setUp()
self.loop = asyncio.new_event_loop()
self.set_event_loop(self.loop)

def test_pidfd_closed_when_waitpid_raises(self):
# _do_wait() must close the pidfd even when waitpid()
# fails with something other than ChildProcessError, otherwise the
# pidfd is leaked
self.loop.set_exception_handler(lambda loop, context: None)

async def coro():
before = os_helper.fd_count()
proc = await asyncio.create_subprocess_exec(
sys.executable, '-c', 'import sys; sys.stdin.read()',
stdin=asyncio.subprocess.PIPE
)

with mock.patch.object(os, 'waitpid',
side_effect=OSError('unexpected')) as m:
proc.stdin.close()
while not m.called:
await asyncio.sleep(0)

os.waitpid(proc.pid, 0)
proc._transport._process_exited(0)
await proc.wait()

self.assertEqual(os_helper.fd_count(), before)

self.loop.run_until_complete(coro())


if __name__ == '__main__':
unittest.main()
3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Library/2026-06-09-19-43-24.gh-issue-151179.hl_6Z0.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
Fix a pidfd leak in ``_PidfdChildWatcher`` on Linux: the watcher no
longer leaks the process file descriptor when ``waitpid()`` fails with an
error other than :exc:`ChildProcessError`.
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