`test_notify` multiprocessing test is flaky

[colesbury]

Bug report

Seen in https://github.com/python/cpython/actions/runs/13606907022/job/38039459160?pr=130732

FAIL: test_notify (test.test_multiprocessing_spawn.test_threads.WithThreadsTestCondition.test_notify)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "D:\a\cpython\cpython\Lib\test\_test_multiprocessing.py", line 1691, in test_notify
    self.assertReturnsIfImplemented(2, get_value, woken)
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^
  File "D:\a\cpython\cpython\Lib\test\_test_multiprocessing.py", line 275, in assertReturnsIfImplemented
    return self.assertEqual(value, res)
           ~~~~~~~~~~~~~~~~^^^^^^^^^^^^
AssertionError: 2 != 1

Linked PRs

• gh-130737: Fix multiprocessing test_notify() #130797
• [3.13] gh-130737: Fix multiprocessing test_notify() (GH-130797) #130802
• [3.12] gh-130737: Fix multiprocessing test_notify() (GH-130797) #130803

[vstinner]

Well, the test uses a sleep of 100 ms as a synchronization method, it's not reliable. I wrote PR #130797 to wait until a condition is met using a loop.