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gh-94673: Recover Weaklist Lookup Performance (gh-95544)
gh-95302 seems to have introduced a small performance regression. Here we make some minor changes to recover that lost performance.
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@ -217,6 +217,16 @@ extern void _Py_PrintReferences(FILE *);
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extern void _Py_PrintReferenceAddresses(FILE *);
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#endif
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/* Return the *address* of the object's weaklist. The address may be
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* dereferenced to get the current head of the weaklist. This is useful
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* for iterating over the linked list of weakrefs, especially when the
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* list is being modified externally (e.g. refs getting removed).
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*
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* The returned pointer should not be used to change the head of the list
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* nor should it be used to add, remove, or swap any refs in the list.
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* That is the sole responsibility of the code in weakrefobject.c.
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*/
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static inline PyObject **
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_PyObject_GET_WEAKREFS_LISTPTR(PyObject *op)
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{
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@ -226,10 +236,33 @@ _PyObject_GET_WEAKREFS_LISTPTR(PyObject *op)
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(PyTypeObject *)op);
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return _PyStaticType_GET_WEAKREFS_LISTPTR(state);
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}
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// Essentially _PyObject_GET_WEAKREFS_LISTPTR_FROM_OFFSET():
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Py_ssize_t offset = Py_TYPE(op)->tp_weaklistoffset;
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return (PyObject **)((char *)op + offset);
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}
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/* This is a special case of _PyObject_GET_WEAKREFS_LISTPTR().
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* Only the most fundamental lookup path is used.
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* Consequently, static types should not be used.
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*
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* For static builtin types the returned pointer will always point
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* to a NULL tp_weaklist. This is fine for any deallocation cases,
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* since static types are never deallocated and static builtin types
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* are only finalized at the end of runtime finalization.
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*
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* If the weaklist for static types is actually needed then use
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* _PyObject_GET_WEAKREFS_LISTPTR().
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*/
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static inline PyWeakReference **
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_PyObject_GET_WEAKREFS_LISTPTR_FROM_OFFSET(PyObject *op)
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{
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assert(!PyType_Check(op) ||
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((PyTypeObject *)op)->tp_flags & Py_TPFLAGS_HEAPTYPE);
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Py_ssize_t offset = Py_TYPE(op)->tp_weaklistoffset;
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return (PyWeakReference **)((char *)op + offset);
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}
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// Fast inlined version of PyObject_IS_GC()
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static inline int
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_PyObject_IS_GC(PyObject *obj)
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@ -794,9 +794,12 @@ handle_weakrefs(PyGC_Head *unreachable, PyGC_Head *old)
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if (! _PyType_SUPPORTS_WEAKREFS(Py_TYPE(op)))
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continue;
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/* It supports weakrefs. Does it have any? */
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wrlist = (PyWeakReference **)
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_PyObject_GET_WEAKREFS_LISTPTR(op);
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/* It supports weakrefs. Does it have any?
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*
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* This is never triggered for static types so we can avoid the
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* (slightly) more costly _PyObject_GET_WEAKREFS_LISTPTR().
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*/
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wrlist = _PyObject_GET_WEAKREFS_LISTPTR_FROM_OFFSET(op);
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/* `op` may have some weakrefs. March over the list, clear
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* all the weakrefs, and move the weakrefs with callbacks
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@ -1505,11 +1505,15 @@ subtype_dealloc(PyObject *self)
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finalizers since they might rely on part of the object
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being finalized that has already been destroyed. */
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if (type->tp_weaklistoffset && !base->tp_weaklistoffset) {
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/* Modeled after GET_WEAKREFS_LISTPTR() */
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PyWeakReference **list = (PyWeakReference **) \
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_PyObject_GET_WEAKREFS_LISTPTR(self);
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while (*list)
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/* Modeled after GET_WEAKREFS_LISTPTR().
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This is never triggered for static types so we can avoid the
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(slightly) more costly _PyObject_GET_WEAKREFS_LISTPTR(). */
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PyWeakReference **list = \
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_PyObject_GET_WEAKREFS_LISTPTR_FROM_OFFSET(self);
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while (*list) {
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_PyWeakref_ClearRef(*list);
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}
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}
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}
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