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gh-153962: Re-raise unexpected OSError in subprocess Popen._internal_poll #153964

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gh-153962: Re-raise unexpected OSError in subprocess Popen._internal_poll #153964

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ba1f9aa
gh-153962: Re-raise unexpected OSError in subprocess Popen._internal_…
fedonman Jul 18, 2026
268c11a
Merge branch 'main' into fix-gh-153962-internal-poll-oserror
fedonman Jul 19, 2026
b37dd6e
Merge branch 'main' into fix-gh-153962-internal-poll-oserror
fedonman Jul 21, 2026
9e11f26
Merge branch 'main' into fix-gh-153962-internal-poll-oserror
fedonman Jul 26, 2026
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7 changes: 7 additions & 0 deletions Lib/subprocess.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2191,6 +2191,13 @@ def _internal_poll(self, _deadstate=None, _del_safe=_del_safe):
# can't get the status.
# http://bugs.python.org/issue15756
self.returncode = 0
else:
# An unexpected error (e.g. EINVAL) must not be
# silently swallowed, leaving returncode as None:
# surface it to the caller. This branch is never
# reached from __del__, which always passes a
# non-None _deadstate.
raise
Comment on lines +2195 to +2200

@serhiy-storchaka serhiy-storchaka Aug 16, 2026

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It harms readability if the comment is 5 times large than the actual code, especially if the code is presumably unreachable. I suggest either to leave a minimal one-line comment or to remove it.

finally:
self._waitpid_lock.release()
return self.returncode
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19 changes: 19 additions & 0 deletions Lib/test/test_subprocess.py
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Original file line number Diff line number Diff line change
Expand Up @@ -3419,6 +3419,25 @@ def test_leak_fast_process_del_killed(self):
else:
self.assertNotIn(ident, [id(o) for o in subprocess._active])

def test_internal_poll_reraises_unexpected_oserror(self):
# An unexpected OSError from waitpid() (i.e. not ECHILD, and not
# during the __del__/_deadstate path) must not be silently swallowed
# by poll(); doing so would leave returncode as None and mask a real
# failure.
p = subprocess.Popen([sys.executable, "-c", "import time; time.sleep(3)"])
self.addCleanup(p.wait)
self.addCleanup(p.kill)

def unexpected_waitpid(pid, flags):
raise OSError(errno.EINVAL, "simulated unexpected error")

with mock.patch.object(subprocess._del_safe, "waitpid",
unexpected_waitpid):
with self.assertRaises(OSError) as cm:
p.poll()
self.assertEqual(cm.exception.errno, errno.EINVAL)
self.assertIsNone(p.returncode)

def test_close_fds_after_preexec(self):
fd_status = support.findfile("fd_status.py", subdir="subprocessdata")

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4 changes: 4 additions & 0 deletions Misc/NEWS.d/next/Library/2026-07-18-16-35-33.gh-issue-153962.Kp7xQ2.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,4 @@
On POSIX, :meth:`subprocess.Popen.poll` now re-raises an unexpected
:exc:`OSError` from the underlying :func:`os.waitpid` call instead of
silently ignoring it and leaving :attr:`!returncode` set to ``None``. The
special handling of :const:`~errno.ECHILD` is unchanged.
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