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WithThreadsTestPool.test_release_task_refs: flaky test or possible free-threading bug #118413
Description
This might be a free-threading related bug or possibly a flaky test. We should investigate and try to figure out the root cause.
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FAIL: test_release_task_refs (test.test_multiprocessing_spawn.test_threads.WithThreadsTestPool.test_release_task_refs)
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Traceback (most recent call last):
File "D:\a\cpython\cpython\Lib\test\_test_multiprocessing.py", line 2817, in test_release_task_refs
self.assertEqual(set(wr() for wr in refs), {None})
~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError: Items in the first set but not the second:
<test._test_multiprocessing.CountedObject object at 0x03E7CA50>
Originally reported by hugovk in #118331 (comment) (https://github.com/python/cpython/actions/runs/8884999534/attempts/1).
Activity
[-]`WithThreadsTestPool.test_release_task_refs `: AssertionError: Items in the first set but not the second[/-][+]`WithThreadsTestPool.test_release_task_refs`: flaky test or possible free-threading bug[/+]pythongh-118413: Temporarily skip `test_release_task_refs` in free-th…
gh-118413: Temporarily skip `test_release_task_refs` in free-threaded…
colesbury commentedon May 1, 2024
I'm able to reproduce this locally on Linux with a few modifications:
First, apply https://gist.github.com/colesbury/f8ba31699eb6fcc79a29a2dd4e41e817 to enable the test and run it in a loop.
Then run multiple test instances in parallel on a single CPU:
colesbury commentedon May 1, 2024
The fix is to move the
time.sleep(DELTA)before thegc.collect():cpython/Lib/test/_test_multiprocessing.py
Lines 2816 to 2817 in c408c36
The
time.sleep()is because the worker processes hold onto the result briefly after it's returned to the main thread. In the free-threaded build, we want thegc.collect()to happen after the workers no longer reference the theCountedObject()values because of the some objects passed across threads have their destructors delayed.pythongh-118413: Fix test_release_task_refs on free-threaded build
gh-118413: Fix test_release_task_refs on free-threaded build (#118494)
colesbury commentedon May 2, 2024
The test is fixed now and re-enabled in the free-threaded build.
pythongh-118413: Temporarily skip `test_release_task_refs` in free-th…
pythongh-118413: Fix test_release_task_refs on free-threaded build (p…