gh-122957: Fix test flakiness in free-thread build

[lesteve]

Fix #122957.

Locally I tested this by running the test 1000 times with the command and the diff below. It fails around 10-20 times out of 1000 on main and does not fail out of 1000 times with the fix on this PR.

./python -m test.test_asyncio.test_threads -k concurrent -v

diff --git a/Lib/test/test_asyncio/test_threads.py b/Lib/test/test_asyncio/test_threads.py
index 774380270a7..8504544aaba 100644
--- a/Lib/test/test_asyncio/test_threads.py
+++ b/Lib/test/test_asyncio/test_threads.py
@@ -63,4 +63,10 @@ def get_ctx():
 
 
 if __name__ == "__main__":
-    unittest.main()
+    nb_tests = 1000
+    suite = unittest.TestSuite(
+        [ToThreadTests("test_to_thread_concurrent") for _ in range(nb_tests)]
+    )
+
+    test_runner = unittest.TextTestRunner()
+    test_runner.run(suite)

• Issue: test_asyncio test_to_thread_concurrent flaky #122957

[ghost]

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[bedevere-app]

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[JelleZijlstra]

Should we backport this to 3.12 and 3.13?

[colesbury]

I think we've only ever seen the flakiness on the free-threaded build, so a backport to 3.12 is probably not necessary, although I think this is a pretty low risk change.

A backport to 3.13 would be good. Otherwise, we'll probably see flaky test failures in the free-threading buildbots. It's not urgent though, and can wait until after the final release if that's more convenient.

[JelleZijlstra]

OK, let's merge this and it'll be up to Thomas whether to merge the 3.13 backport, or we can just do it after 3.13.0 goes out.

[miss-islington-app]

Thanks @lesteve for the PR, and @JelleZijlstra for merging it 🌮🎉.. I'm working now to backport this PR to: 3.13.
🐍🍒⛏🤖

[bedevere-app]

GH-124067 is a backport of this pull request to the 3.13 branch.