test_threading: test_default_timeout() fails randomly ands logs "Warning -- Unraisable exception"

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Example from issue #108987:

test_default_timeout (test.test_threading.BarrierTests.test_default_timeout)
Test the barrier's default timeout ... Warning -- Unraisable exception
Exception ignored in thread started by: <function Bunch.__init__.<locals>.task at 0x053F5270>
Traceback (most recent call last):
  File "D:\a\cpython\cpython\Lib\test\lock_tests.py", line 48, in task
    f()
  File "D:\a\cpython\cpython\Lib\test\lock_tests.py", line 1020, in f
    i = barrier.wait()
        ^^^^^^^^^^^^^^
  File "D:\a\cpython\cpython\Lib\threading.py", line 709, in wait
    self._wait(timeout)
  File "D:\a\cpython\cpython\Lib\threading.py", line 749, in _wait
    raise BrokenBarrierError
threading.BrokenBarrierError: 
ERROR
test_repr (test.test_threading.BarrierTests.test_repr) ... Warning -- Unraisable exception
Exception ignored in thread started by: <function Bunch.__init__.<locals>.task at 0x053F5270>
Traceback (most recent call last):
  File "D:\a\cpython\cpython\Lib\test\lock_tests.py", line 48, in task
    f()
  File "D:\a\cpython\cpython\Lib\test\lock_tests.py", line 1020, in f
    i = barrier.wait()
        ^^^^^^^^^^^^^^
  File "D:\a\cpython\cpython\Lib\threading.py", line 709, in wait
    self._wait(timeout)
  File "D:\a\cpython\cpython\Lib\threading.py", line 749, in _wait
    raise BrokenBarrierError
threading.BrokenBarrierError: 
Warning -- Unraisable exception
Exception ignored in thread started by: <function Bunch.__init__.<locals>.task at 0x053F5270>
Traceback (most recent call last):
  File "D:\a\cpython\cpython\Lib\test\lock_tests.py", line 48, in task
    f()
  File "D:\a\cpython\cpython\Lib\test\lock_tests.py", line 1020, in f
    i = barrier.wait()
        ^^^^^^^^^^^^^^
  File "D:\a\cpython\cpython\Lib\threading.py", line 709, in wait
    self._wait(timeout)
  File "D:\a\cpython\cpython\Lib\threading.py", line 749, in _wait
    raise BrokenBarrierError
threading.BrokenBarrierError: 
Warning -- Unraisable exception
Exception ignored in thread started by: <function Bunch.__init__.<locals>.task at 0x053F5270>
Traceback (most recent call last):
  File "D:\a\cpython\cpython\Lib\test\lock_tests.py", line 48, in task
    f()
  File "D:\a\cpython\cpython\Lib\test\lock_tests.py", line 1020, in f
    i = barrier.wait()
        ^^^^^^^^^^^^^^
  File "D:\a\cpython\cpython\Lib\threading.py", line 700, in wait
    self._enter() # Block while the barrier drains.
    ^^^^^^^^^^^^^
  File "D:\a\cpython\cpython\Lib\threading.py", line 724, in _enter
    raise BrokenBarrierError
threading.BrokenBarrierError: 
ok

build: https://github.com/python/cpython/actions/runs/6094370280/job/16535778004#step:5:103

In issue #108987, I fixed a crashed which occurred in this test when the test failed.

I create this issue to focus on the test failure and Warning -- Unraisable exception.

Linked PRs

• gh-109401: Fix threading barrier test_default_timeout() #109875
• [3.12] gh-109401: Fix threading barrier test_default_timeout() (GH-109875) #109876
• [3.11] gh-109401: Fix threading barrier test_default_timeout() (GH-109875) #109877

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Issue #108987 contains instructions on how to reproduce the bug and which platforms are affected. The test failure seems to be way more likely on Windows.

cc @serhiy-storchaka