Document _PyType_CacheInitForSpecialization

Author: mpage

Include/internal/pycore_object.h

@@ -822,8 +822,18 @@ extern bool _PyObject_TryGetInstanceAttribute(PyObject *obj, PyObject *name,
                                               PyObject **attr);
 extern PyObject *_PyType_LookupRefAndVersion(PyTypeObject *, PyObject *,
                                              unsigned int *);
-extern int _PyType_CacheInitForSpecialization(PyTypeObject *, PyObject *,
-                                              unsigned int);
+
+// Cache the provided init method in the specialization cache of type if the
+// provided type version matches the current version of the type.
+//
+// The cached value is borrowed and is only valid if guarded by a type
+// version check. In free-threaded builds the init method must also use
+// deferred reference counting.
+//
+// Returns 1 if the value was cached or 0 otherwise.
+extern int _PyType_CacheInitForSpecialization(PyHeapTypeObject *type,
+                                              PyObject *init,
+                                              unsigned int tp_version);
 
 #ifdef Py_GIL_DISABLED
 #  define MANAGED_DICT_OFFSET    (((Py_ssize_t)sizeof(PyObject *))*-1)

Objects/typeobject.c

@@ -5658,23 +5658,21 @@ _PyType_Lookup(PyTypeObject *type, PyObject *name)
     return res;
 }
 
-
 int
-_PyType_CacheInitForSpecialization(PyTypeObject *type, PyObject *init,
+_PyType_CacheInitForSpecialization(PyHeapTypeObject *type, PyObject *init,
                                    unsigned int tp_version)
 {
     if (!init || !tp_version) {
         return 0;
     }
     int can_cache;
     BEGIN_TYPE_LOCK();
-    can_cache = type->tp_version_tag == tp_version;
+    can_cache = ((PyTypeObject*)type)->tp_version_tag == tp_version;
     #ifdef Py_GIL_DISABLED
     can_cache = can_cache && _PyObject_HasDeferredRefcount(init);
     #endif
     if (can_cache) {
-        PyHeapTypeObject *ht = (PyHeapTypeObject*) type;
-        FT_ATOMIC_STORE_PTR_RELAXED(ht->_spec_cache.init, init);
+        FT_ATOMIC_STORE_PTR_RELAXED(type->_spec_cache.init, init);
     }
     END_TYPE_LOCK();
     return can_cache;

Python/specialize.c

@@ -1992,7 +1992,8 @@ specialize_class_call(PyObject *callable, _Py_CODEUNIT *instr, int nargs)
             Py_XDECREF(init);
             return -1;
         }
-        if (init != NULL && _PyType_CacheInitForSpecialization(tp, init, tp_version)) {
+        if (init != NULL && _PyType_CacheInitForSpecialization(
+                                (PyHeapTypeObject *)tp, init, tp_version)) {
             _PyCallCache *cache = (_PyCallCache *)(instr + 1);
             write_u32(cache->func_version, tp_version);
             specialize(instr, CALL_ALLOC_AND_ENTER_INIT);