[issue40115] test_asyncio leaked [3, 3, 3] references, sum=9

[STINNER Victor]

STINNER Victor <vstinner at python.org> added the comment:

The leak was introduced by:

commit b61b818d916942aad1f8f3e33181801c4a1ed14b (HEAD, refs/bisect/bad)
Author: Kyle Stanley <aeros167 at gmail.com>
Date:   Fri Mar 27 15:31:22 2020 -0400

    bpo-39812: Remove daemon threads in concurrent.futures (GH-19149)
    
    Remove daemon threads from :mod:`concurrent.futures` by adding
    an internal `threading._register_atexit()`, which calls registered functions
    prior to joining all non-daemon threads. This allows for compatibility
    with subinterpreters, which don't support daemon threads.

The leaking test is:

$ ./python -m test --fail-env-changed -R 3:3 test_asyncio -m test.test_asyncio.test_events.EPollEventLoopTests.test_run_in_executor_cancel
0:00:00 load avg: 0.56 Run tests sequentially
0:00:00 load avg: 0.56 [1/1] test_asyncio
beginning 6 repetitions
123456
......
test_asyncio leaked [1, 1, 1] references, sum=3
test_asyncio leaked [2, 1, 1] memory blocks, sum=4
test_asyncio failed

== Tests result: FAILURE ==

1 test failed:
    test_asyncio

Total duration: 4.2 sec
Tests result: FAILURE

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<https://bugs.python.org/issue40115>
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