https://github.com/python/cpython/commit/cedff2d617c79e2122162049bb75e1d690d9f5eb commit: cedff2d617c79e2122162049bb75e1d690d9f5eb branch: 3.14 author: Miss Islington (bot) <[email protected]> committer: colesbury <[email protected]> date: 2026-03-12T14:33:05-04:00 summary:
[3.14] gh-145685: Improve scaling of type attribute lookups (gh-145774) (#145874) Avoid locking in the PyType_Lookup cache-miss path if the type's tp_version_tag is already valid. (cherry picked from commit cd5217283112d41c0244e2d96302cbe33f0b4cb1) Co-authored-by: Sam Gross <[email protected]> files: A Misc/NEWS.d/next/Core_and_Builtins/2026-03-10-12-52-06.gh-issue-145685.80B7gK.rst M Include/internal/pycore_pyatomic_ft_wrappers.h M Objects/typeobject.c diff --git a/Include/internal/pycore_pyatomic_ft_wrappers.h b/Include/internal/pycore_pyatomic_ft_wrappers.h index f4c699616a17c4..be0335a2389c0a 100644 --- a/Include/internal/pycore_pyatomic_ft_wrappers.h +++ b/Include/internal/pycore_pyatomic_ft_wrappers.h @@ -87,6 +87,8 @@ extern "C" { _Py_atomic_store_int_relaxed(&value, new_value) #define FT_ATOMIC_LOAD_INT_RELAXED(value) \ _Py_atomic_load_int_relaxed(&value) +#define FT_ATOMIC_LOAD_UINT(value) \ + _Py_atomic_load_uint(&value) #define FT_ATOMIC_STORE_UINT_RELAXED(value, new_value) \ _Py_atomic_store_uint_relaxed(&value, new_value) #define FT_ATOMIC_LOAD_UINT_RELAXED(value) \ @@ -158,6 +160,7 @@ extern "C" { #define FT_ATOMIC_STORE_INT(value, new_value) value = new_value #define FT_ATOMIC_LOAD_INT_RELAXED(value) value #define FT_ATOMIC_STORE_INT_RELAXED(value, new_value) value = new_value +#define FT_ATOMIC_LOAD_UINT(value) value #define FT_ATOMIC_LOAD_UINT_RELAXED(value) value #define FT_ATOMIC_STORE_UINT_RELAXED(value, new_value) value = new_value #define FT_ATOMIC_LOAD_LONG_RELAXED(value) value diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2026-03-10-12-52-06.gh-issue-145685.80B7gK.rst b/Misc/NEWS.d/next/Core_and_Builtins/2026-03-10-12-52-06.gh-issue-145685.80B7gK.rst new file mode 100644 index 00000000000000..da34b67c952c7c --- /dev/null +++ b/Misc/NEWS.d/next/Core_and_Builtins/2026-03-10-12-52-06.gh-issue-145685.80B7gK.rst @@ -0,0 +1,2 @@ +Improve scaling of type attribute lookups in the :term:`free-threaded build` by +avoiding contention on the internal type lock. diff --git a/Objects/typeobject.c b/Objects/typeobject.c index 9777055c5f2313..e6b30615e2ade2 100644 --- a/Objects/typeobject.c +++ b/Objects/typeobject.c @@ -51,8 +51,8 @@ class object "PyObject *" "&PyBaseObject_Type" MCACHE_HASH(FT_ATOMIC_LOAD_UINT32_RELAXED((type)->tp_version_tag), \ ((Py_ssize_t)(name)) >> 3) #define MCACHE_CACHEABLE_NAME(name) \ - PyUnicode_CheckExact(name) && \ - (PyUnicode_GET_LENGTH(name) <= MCACHE_MAX_ATTR_SIZE) + (PyUnicode_CheckExact(name) && \ + (PyUnicode_GET_LENGTH(name) <= MCACHE_MAX_ATTR_SIZE)) #define NEXT_VERSION_TAG(interp) \ (interp)->types.next_version_tag @@ -5708,8 +5708,6 @@ PyObject_GetItemData(PyObject *obj) static int find_name_in_mro(PyTypeObject *type, PyObject *name, _PyStackRef *out) { - ASSERT_TYPE_LOCK_HELD(); - Py_hash_t hash = _PyObject_HashFast(name); if (hash == -1) { PyErr_Clear(); @@ -5860,6 +5858,14 @@ _PyType_LookupRefAndVersion(PyTypeObject *type, PyObject *name, unsigned int *ve return PyStackRef_AsPyObjectSteal(out); } +static int +should_assign_version_tag(PyTypeObject *type, PyObject *name, unsigned int version_tag) +{ + return (version_tag == 0 + && FT_ATOMIC_LOAD_UINT16_RELAXED(type->tp_versions_used) < MAX_VERSIONS_PER_CLASS + && MCACHE_CACHEABLE_NAME(name)); +} + unsigned int _PyType_LookupStackRefAndVersion(PyTypeObject *type, PyObject *name, _PyStackRef *out) { @@ -5908,24 +5914,20 @@ _PyType_LookupStackRefAndVersion(PyTypeObject *type, PyObject *name, _PyStackRef /* We may end up clearing live exceptions below, so make sure it's ours. */ assert(!PyErr_Occurred()); - // We need to atomically do the lookup and capture the version before - // anyone else can modify our mro or mutate the type. - int res; PyInterpreterState *interp = _PyInterpreterState_GET(); - int has_version = 0; - unsigned int assigned_version = 0; - BEGIN_TYPE_LOCK(); - // We must assign the version before doing the lookup. If - // find_name_in_mro() blocks and releases the critical section - // then the type version can change. - if (MCACHE_CACHEABLE_NAME(name)) { - has_version = assign_version_tag(interp, type); - assigned_version = type->tp_version_tag; - } - res = find_name_in_mro(type, name, out); - END_TYPE_LOCK(); + unsigned int version_tag = FT_ATOMIC_LOAD_UINT(type->tp_version_tag); + if (should_assign_version_tag(type, name, version_tag)) { + BEGIN_TYPE_LOCK(); + assign_version_tag(interp, type); + version_tag = type->tp_version_tag; + res = find_name_in_mro(type, name, out); + END_TYPE_LOCK(); + } + else { + res = find_name_in_mro(type, name, out); + } /* Only put NULL results into cache if there was no error. */ if (res < 0) { @@ -5933,16 +5935,18 @@ _PyType_LookupStackRefAndVersion(PyTypeObject *type, PyObject *name, _PyStackRef return 0; } - if (has_version) { - PyObject *res_obj = PyStackRef_AsPyObjectBorrow(*out); + if (version_tag == 0 || !MCACHE_CACHEABLE_NAME(name)) { + return 0; + } + + PyObject *res_obj = PyStackRef_AsPyObjectBorrow(*out); #if Py_GIL_DISABLED - update_cache_gil_disabled(entry, name, assigned_version, res_obj); + update_cache_gil_disabled(entry, name, version_tag, res_obj); #else - PyObject *old_value = update_cache(entry, name, assigned_version, res_obj); - Py_DECREF(old_value); + PyObject *old_value = update_cache(entry, name, version_tag, res_obj); + Py_DECREF(old_value); #endif - } - return has_version ? assigned_version : 0; + return version_tag; } /* Internal API to look for a name through the MRO. _______________________________________________ Python-checkins mailing list -- [email protected] To unsubscribe send an email to [email protected] https://mail.python.org/mailman3//lists/python-checkins.python.org Member address: [email protected]
