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gh-117657: Use an atomic store to set type flags. - #127588
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The `PyType_HasFeature()` function reads the flags with a relaxed atomic load and without holding the type lock. To avoid data races, use atomic stores if `PyType_Ready()` has already been called.
colesbury
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Dec 4, 2024
colesbury
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Overall, looks good to me. I think type_set_flags can be simplified and I have a question below about locking.
Just use FT_ATOMIC_STORE_ULONG_RELAXED() always, not worth the extra code complexity.
This helps ensure that type flag setting is done in a free-threading safe way. Fix a few cases were flags were set without holding the type lock. Use `type_modified_unlocked()` in a couple places where the lock is already head.
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The
PyType_HasFeature()function reads the flags with a relaxed atomic load and without holding the type lock. To avoid data races, use atomic stores to update the type flags.This change eliminates some warnings from TSAN. For non-free-threaded builds, there should be no performance impact.