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gh-157184: Scale the join() alarm in the multiprocessing kill tests #157185

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gh-157184: Scale the join() alarm in the multiprocessing kill tests #157185

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fe2551d
gh-157184: Scale the join() alarm in the multiprocessing kill tests
iamsharduld Sep 8, 2026
f1e0152
Remove the NEWS entry
iamsharduld Sep 8, 2026
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gh-157184: Scale the join() alarm in the multiprocessing kill tests 
_kill_process() interrupts the join() of the killed child with SIGALRM so
that a blocked waitpid() becomes a readable error instead of a hang, but
the alarm has been a fixed 10 seconds since 2013. On a build slow enough
that reaping the child legitimately takes longer, it fires on a healthy
run: seen on the UBSan CI job, where the alarm interrupted os.waitpid()
itself.

Use support.LONG_TIMEOUT, which is documented for detecting hangs and is
scaled by regrtest for slow workers, as the same function already does
for its event wait.
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@iamsharduld
iamsharduld committed Sep 8, 2026
commit fe2551d6dc98491157ae90e6de3952149998e112
6 changes: 5 additions & 1 deletion Lib/test/_test_multiprocessing.py
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Expand Up @@ -9,6 +9,7 @@
import time
import io
import itertools
import math
import sys
import os
import gc
Expand Down Expand Up @@ -624,11 +625,14 @@ def _kill_process(self, meth,>
if hasattr(signal, 'alarm'):
# On the Gentoo buildbot waitpid() often seems to block forever.
# We use alarm() to interrupt it if it blocks for too long.
# The timeout only has to catch a hang, so use LONG_TIMEOUT:
# a shorter one fires on a slow build where reaping the child
# legitimately takes a while.
def handler(*args):
raise RuntimeError('join took too long: %s' % p)
old_handler = signal.signal(signal.SIGALRM, handler)
try:
signal.alarm(10)
signal.alarm(math.ceil(support.LONG_TIMEOUT))
self.assertEqual(join(), None)
finally:
signal.alarm(0)
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5 changes: 5 additions & 0 deletions Misc/NEWS.d/next/Tests/2026-09-08-14-05-00.gh-issue-157184.nKPZhX.rst
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@@ -0,0 +1,5 @@
Fix the ``multiprocessing`` tests that kill a child process
(``test_interrupt``, ``test_interrupt_no_handler``, ``test_terminate`` and
``test_kill``) failing on slow builds: the alarm guarding the ``join()`` of
the killed child used a fixed 10 second timeout, and now uses
:data:`~test.support.LONG_TIMEOUT`, which regrtest scales.
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