…onGH-26103)
When a Thread is not joined after it has stopped, its lock may remain in the _shutdown_locks set until interpreter shutdown.  If many threads are created this way, the _shutdown_locks set could therefore grow endlessly.  To avoid such a situation, purge expired locks each time a new one is added or removed..
(cherry picked from commit  c10c2ec )
Co-authored-by: Antoine Pitrou <antoine@python.org>

…26103) (GH-26138)
When a Thread is not joined after it has stopped, its lock may remain in the _shutdown_locks set until interpreter shutdown.  If many threads are created this way, the _shutdown_locks set could therefore grow endlessly.  To avoid such a situation, purge expired locks each time a new one is added or removed.
(cherry picked from commit  c10c2ec )
Co-authored-by: Antoine Pitrou <antoine@python.org>

…6103) (GH-26142)
When a Thread is not joined after it has stopped, its lock may remain in the _shutdown_locks set until interpreter shutdown.  If many threads are created this way, the _shutdown_locks set could therefore grow endlessly.  To avoid such a situation, purge expired locks each time a new one is added or removed..
(cherry picked from commit  c10c2ec )
Co-authored-by: Antoine Pitrou <antoine@python.org>
Automerge-Triggered-By: GH:pitrou

Note that the previous code was not thread-safe. A thread-safe version would have been:
for t in list(threads):
    if not t.is_alive():
        # A set is used for `threads`, because `set.discard()` is O(1) but `list.remove()` is O(n).
        threads.discard(t)
        # Python 3.8 and below has a memory leak. python/cpython#26103
        t.join()