Feature or enhancement

CPython uses freelists for frequently allocated Python objects, like dict, list, and slice. There freelists are generally stored in the per-interpreter state, which is not thread-safe without the GIL. In --disable-gil builds, the freelists should be stored in the per-thread state (i.e., PyThreadState). I think we probably want to keep the freelists in the interpreter state for the default build. This will probably require some refactoring.

Freelists:

• float
• slice (slice_cache)
• tuple
• list
• dict (PyDictKeysObject and PyDictObject)
• generator (value_freelist and asend_freelist)
• PyContext

For context, here are similar changes in the nogil-3.12 fork, but I expect the changes in CPython 3.13 to be a bit different:

• colesbury/nogil-3.12@07f5f8c318
• colesbury/nogil-3.12@2a4c17e896

Linked PRs

• gh-111968: Introduce _PyFreeListState and _PyFreeListState_GET API #113584
• gh-111968: Use per-thread freelists for float in free-threading #113886
• gh-111968: Unify naming scheme for freelist #113919
• gh-111968: Use per-thread freelists for tuple in free-threading #113921
• gh-111968: Explicit handling for finalized freelist #113929
• gh-111968: Use per-thread slice_cache in free-threading #113972
• gh-111968: Use per-thread freelists for PyContext in free-threading #114122
• gh-111968: Use per-thread freelists for generator in free-threading #114189
• gh-111968: Fix --without-freelists build #114270
• gh-111968: Use per-thread freelists for dict in free-threading #114323
• gh-111968: Unify freelist naming schema to Eric's suggestion #114581
• gh-111968: Refactor _PyXXX_Fini to integrate with _PyObject_ClearFreeLists #114899
• gh-111968: Rename freelist related struct names to Eric's suggestion #115329
• gh-111968: Split _Py_dictkeys_freelist out of _Py_dict_freelist #115505
• gh-111968: Split _Py_async_gen_asend_freelist out of _Py_async_gen_fr… #115546
• gh-111968: remove redundant fetching of interpreter state in dict implementation  #136673