https://github.com/python/cpython
Revision 5d21d884b6ffa45dac50a5f9a07c41356a8478b4 authored by mpage on 29 March 2024, 17:42:02 UTC, committed by GitHub on 29 March 2024, 17:42:02 UTC
Read the MRO in a thread-unsafe way in `PyType_IsSubtype` to avoid locking. Fixing this is tracked in #117306. The motivation for this change is in support of making weakrefs thread-safe in free-threaded builds: `WeakValueDictionary` uses a special dictionary function, `_PyDict_DelItemIf` to remove dead weakrefs from the dictionary. `_PyDict_DelItemIf` removes a key if a user supplied predicate evaluates to true for the value associated with the key. Crucially for the `WeakValueDictionary` use case, the predicate evaluation + deletion sequence is atomic, provided that the predicate doesn’t suspend. The predicate used by `WeakValueDictionary` includes a subtype check, which we must ensure doesn't suspend in free-threaded builds.
1 parent 19c1dd6
Tip revision: 5d21d884b6ffa45dac50a5f9a07c41356a8478b4 authored by mpage on 29 March 2024, 17:42:02 UTC
gh-111926: Avoid locking in PyType_IsSubtype (#117275)
gh-111926: Avoid locking in PyType_IsSubtype (#117275)
Tip revision: 5d21d88
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