gh-109917: Fix test instability in test_concurrent_futures

[elfstrom]

The test had an instability issue due to the ordering of the dummy queue operation and the real wakeup pipe operations. Both primitives are thread safe but not done atomically as a single update and may interleave arbitrarily. With the old order of operations this can lead to an incorrect state where the dummy queue is full but the wakeup pipe is empty. By swapping the order in clear() I think this can no longer happen in any possible operation interleaving (famous last words).

This is a minimal update to fix the issue. Long term it might be better to rewrite the test along the lines of #110129 where we make it possible to override the wakeup message and cause the blocking behaviour that way instead of the small dummy queue used now. Less mocking is usually better and the test can be faster as well. It does require a minor modification to the implementation and there were other issues in #110129 but the general test idea seems better than the current solution.

• Issue: test_concurrent_futures: test_gh105829_should_not_deadlock_if_wakeup_pipe_full() hangs on ARM64 macOS 3.x #109917

[miss-islington]

Thanks @elfstrom for the PR, and @cjw296 for merging it 🌮🎉.. I'm working now to backport this PR to: 3.12.
🐍🍒⛏🤖

[miss-islington]

Thanks @elfstrom for the PR, and @cjw296 for merging it 🌮🎉.. I'm working now to backport this PR to: 3.11.
🐍🍒⛏🤖

[bedevere-app]

GH-110315 is a backport of this pull request to the 3.12 branch.

[bedevere-app]

GH-110316 is a backport of this pull request to the 3.11 branch.

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot AMD64 FreeBSD 3.x has failed when building commit a376a72.

What do you need to do:

1. Don't panic.
2. Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
3. Go to the page of the buildbot that failed (https://buildbot.python.org/all/#builders/1223/builds/326) and take a look at the build logs.
4. Check if the failure is related to this commit (a376a72) or if it is a false positive.
5. If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/all/#builders/1223/builds/326

Summary of the results of the build (if available):

==

Click to see traceback logs

Traceback (most recent call last):
  File "<frozen importlib._bootstrap>", line 1354, in _find_and_load
  File "<frozen importlib._bootstrap>", line 1316, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 1256, in _find_spec
  File "<frozen importlib._bootstrap_external>", line 1538, in find_spec
  File "<frozen importlib._bootstrap_external>", line 1512, in _get_spec
  File "<frozen importlib._bootstrap_external>", line 1630, in find_spec
  File "<frozen importlib._bootstrap_external>", line 161, in _path_isfile
  File "<frozen importlib._bootstrap_external>", line 153, in _path_is_mode_type
  File "<frozen importlib._bootstrap_external>", line 147, in _path_stat
ValueError: embedded null byte


Traceback (most recent call last):
  File "/buildbot/buildarea/3.x.ware-freebsd/build/Lib/threading.py", line 1067, in _bootstrap_inner
    self.run()
  File "/buildbot/buildarea/3.x.ware-freebsd/build/Lib/threading.py", line 1004, in run
    self._target(*self._args, **self._kwargs)
  File "/buildbot/buildarea/3.x.ware-freebsd/build/Lib/test/test_interpreters.py", line 584, in task
    interp = interpreters.create()
             ^^^^^^^^^^^^^^^^^^^^^
  File "/buildbot/buildarea/3.x.ware-freebsd/build/Lib/test/support/interpreters.py", line 26, in create
    id = _interpreters.create(isolated=isolated)
         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
RuntimeError: interpreter creation failed
k

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot s390x Fedora 3.x has failed when building commit a376a72.

What do you need to do:

1. Don't panic.
2. Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
3. Go to the page of the buildbot that failed (https://buildbot.python.org/all/#builders/223/builds/4604) and take a look at the build logs.
4. Check if the failure is related to this commit (a376a72) or if it is a false positive.
5. If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/all/#builders/223/builds/4604

Failed tests:

• test_subprocess

Failed subtests:

• test_pipesize_default - test.test_subprocess.ProcessTestCaseNoPoll.test_pipesize_default

Summary of the results of the build (if available):

==

Click to see traceback logs

Traceback (most recent call last):
  File "/home/dje/cpython-buildarea/3.x.edelsohn-fedora-z/build/Lib/test/test_subprocess.py", line 763, in test_pipesize_default
    self.assertEqual(
AssertionError: 65536 != 8192

[vstinner]

Thanks for the fix :-)