Lock contention inside `_PyType_LookupRef`

Feature or enhancement

Proposal:

As part of adding free-threading support to LibCST, we noticed there is a lot of lock contention on TYPE_LOCK inside the _PyType_LookupRef function. In the LibCST, the common "visitor" pattern is used. For example, in the _visitors.py module there is the code:

visit_func = getattr(self, f"visit_{type(node).__name__}", None)

The second argument to getattr() is a non-interned string and it causes the cached and lock-free path of _PyType_LookupRef() never to be taken. Instead, the TYPE_LOCK mutex is acquired on each lookup. This obviously scales very badly if there are multiple threads looking up class methods using this pattern.

Testing was done with Python 3.13 but I believe the same issue exists with 3.14.

Has this already been discussed elsewhere?

This is a minor feature, which does not need previous discussion elsewhere

Links to previous discussion of this feature:

No response

Linked PRs

• gh-132381
• gh-131174
• gh-132651
• gh-132652
• gh-133669
• gh-135112

まず CPython の _PyType_LookupRef と TYPE_LOCK パスを読み、次に LibCST の _visitors.py にある visitor パターンを調べます。Python 3.13 と 3.14 での動作を比較し、リンクされている PR を確認します。完了条件には、ロック競合に対処する合意済みの変更と、lookup パスのスケーラビリティが向上したことを示す証拠を含める必要があります。