[3.12] gh-109917: Fix test instability in test_concurrent_futures (GH-110306) (#110315)

gh-109917: Fix test instability in test_concurrent_futures (GH-110306)

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).
(cherry picked from commit a376a72bd92cd7c9930467dd1aba40045fb75e3b)

Co-authored-by: elfstrom <elfstrom@users.noreply.github.com>

diff --git a/Lib/test/test_concurrent_futures/test_deadlock.py b/Lib/test/test_concurrent_futures/test_deadlock.py
index 7ede95d5ed3422bccec043be8157c99ed363e59f..1db4cd009926b9bc7a300c24b1d31f0f0b891de8 100644 (file)
--- a/Lib/test/test_concurrent_futures/test_deadlock.py
+++ b/Lib/test/test_concurrent_futures/test_deadlock.py
@@ -284,11 +284,12 @@ class ExecutorDeadlockTest:
                 super().wakeup()
 
             def clear(self):
+                super().clear()
                 try:
                     while True:
                         self._dummy_queue.get_nowait()
                 except queue.Empty:
-                    super().clear()
+                    pass
 
         with (unittest.mock.patch.object(futures.process._ExecutorManagerThread,
                                          'run', mock_run),