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.
This commit is contained in:
Eric Snow 2022-08-04 11:28:15 -06:00 committed by GitHub
parent 60f54d9485
commit bdbadb905a
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GPG Key ID: 4AEE18F83AFDEB23
3 changed files with 47 additions and 7 deletions

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@ -217,6 +217,16 @@ extern void _Py_PrintReferences(FILE *);
extern void _Py_PrintReferenceAddresses(FILE *);
#endif
/* Return the *address* of the object's weaklist. The address may be
* dereferenced to get the current head of the weaklist. This is useful
* for iterating over the linked list of weakrefs, especially when the
* list is being modified externally (e.g. refs getting removed).
*
* The returned pointer should not be used to change the head of the list
* nor should it be used to add, remove, or swap any refs in the list.
* That is the sole responsibility of the code in weakrefobject.c.
*/
static inline PyObject **
_PyObject_GET_WEAKREFS_LISTPTR(PyObject *op)
{
@ -226,10 +236,33 @@ _PyObject_GET_WEAKREFS_LISTPTR(PyObject *op)
(PyTypeObject *)op);
return _PyStaticType_GET_WEAKREFS_LISTPTR(state);
}
// Essentially _PyObject_GET_WEAKREFS_LISTPTR_FROM_OFFSET():
Py_ssize_t offset = Py_TYPE(op)->tp_weaklistoffset;
return (PyObject **)((char *)op + offset);
}
/* This is a special case of _PyObject_GET_WEAKREFS_LISTPTR().
* Only the most fundamental lookup path is used.
* Consequently, static types should not be used.
*
* For static builtin types the returned pointer will always point
* to a NULL tp_weaklist. This is fine for any deallocation cases,
* since static types are never deallocated and static builtin types
* are only finalized at the end of runtime finalization.
*
* If the weaklist for static types is actually needed then use
* _PyObject_GET_WEAKREFS_LISTPTR().
*/
static inline PyWeakReference **
_PyObject_GET_WEAKREFS_LISTPTR_FROM_OFFSET(PyObject *op)
{
assert(!PyType_Check(op) ||
((PyTypeObject *)op)->tp_flags & Py_TPFLAGS_HEAPTYPE);
Py_ssize_t offset = Py_TYPE(op)->tp_weaklistoffset;
return (PyWeakReference **)((char *)op + offset);
}
// Fast inlined version of PyObject_IS_GC()
static inline int
_PyObject_IS_GC(PyObject *obj)

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@ -794,9 +794,12 @@ handle_weakrefs(PyGC_Head *unreachable, PyGC_Head *old)
if (! _PyType_SUPPORTS_WEAKREFS(Py_TYPE(op)))
continue;
/* It supports weakrefs. Does it have any? */
wrlist = (PyWeakReference **)
_PyObject_GET_WEAKREFS_LISTPTR(op);
/* It supports weakrefs. Does it have any?
*
* This is never triggered for static types so we can avoid the
* (slightly) more costly _PyObject_GET_WEAKREFS_LISTPTR().
*/
wrlist = _PyObject_GET_WEAKREFS_LISTPTR_FROM_OFFSET(op);
/* `op` may have some weakrefs. March over the list, clear
* all the weakrefs, and move the weakrefs with callbacks

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@ -1505,11 +1505,15 @@ subtype_dealloc(PyObject *self)
finalizers since they might rely on part of the object
being finalized that has already been destroyed. */
if (type->tp_weaklistoffset && !base->tp_weaklistoffset) {
/* Modeled after GET_WEAKREFS_LISTPTR() */
PyWeakReference **list = (PyWeakReference **) \
_PyObject_GET_WEAKREFS_LISTPTR(self);
while (*list)
/* Modeled after GET_WEAKREFS_LISTPTR().
This is never triggered for static types so we can avoid the
(slightly) more costly _PyObject_GET_WEAKREFS_LISTPTR(). */
PyWeakReference **list = \
_PyObject_GET_WEAKREFS_LISTPTR_FROM_OFFSET(self);
while (*list) {
_PyWeakref_ClearRef(*list);
}
}
}