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Expand Up		@@ -59,12 +59,31 @@ rules:
		Analogous to :c:func:`PyObject_New` but for container objects with the
		:const:`Py_TPFLAGS_HAVE_GC` flag set.


		.. c:function:: TYPE* PyObject_GC_NewVar(TYPE, PyTypeObject *type, Py_ssize_t size)

		Analogous to :c:func:`PyObject_NewVar` but for container objects with the
		:const:`Py_TPFLAGS_HAVE_GC` flag set.

		.. c:function:: PyObject* PyUnstable_Object_GC_NewWithExtraData(PyTypeObject *type, size_t extra_size)

		Analogous to :c:func:`PyObject_GC_New` but allocates extra_size
		bytes at the end of the object (at offset
		:c:member:`~PyTypeObject.tp_basicsize`).
		The allocated memory is initialized to zeros,
		except for the :c:type:`Python object header <PyObject>`.

		The extra data will be deallocated with the object, but otherwise it is
		not managed by Python.

		.. warning::
		The function is marked as unstable because the final mechanism
		for reserving extra data after an instance is not yet decided.
		For allocating a variable number of fields, prefer using
		:c:type:`PyVarObject` and :c:member:`~PyTypeObject.tp_itemsize`
		instead.

		.. versionadded:: 3.12


		.. c:function:: TYPE* PyObject_GC_Resize(TYPE, PyVarObject *op, Py_ssize_t newsize)

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3 changes: 3 additions & 0 deletions 3 Include/cpython/objimpl.h

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Original file line number	Diff line number	Diff line change
Expand Up		@@ -90,3 +90,6 @@ PyAPI_FUNC(int) PyObject_IS_GC(PyObject *obj);
		PyAPI_FUNC(int) PyType_SUPPORTS_WEAKREFS(PyTypeObject *type);

		PyAPI_FUNC(PyObject *) PyObject_GET_WEAKREFS_LISTPTR(PyObject op);

		PyAPI_FUNC(PyObject ) PyUnstable_Object_GC_NewWithExtraData(PyTypeObject ,
		size_t);

14 changes: 14 additions & 0 deletions 14 Lib/test/test_capi/test_misc.py

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Original file line number	Diff line number	Diff line change
Expand Up		@@ -1043,6 +1043,20 @@ class dictsub(dict): ... # dict subclasses must work
		self.assertEqual(_testcapi.function_get_kw_defaults(some), None)
		self.assertEqual(some.__kwdefaults__, None)

		def test_unstable_gc_new_with_extra_data(self):
		class Data(_testcapi.ObjExtraData):
		__slots__ = ('x', 'y')

		d = Data()
		d.x = 10
		d.y = 20
		d.extra = 30
		self.assertEqual(d.x, 10)
		self.assertEqual(d.y, 20)
		self.assertEqual(d.extra, 30)
		del d.extra
		self.assertIsNone(d.extra)


		class TestPendingCalls(unittest.TestCase):

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2 changes: 2 additions & 0 deletions 2 Misc/NEWS.d/next/C API/2023-04-24-10-31-59.gh-issue-103743.2xYA1K.rst

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Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,2 @@
		Add :c:func:`PyUnstable_Object_GC_NewWithExtraData` function that can be used to
		allocate additional memory after an object for data not managed by Python.

105 changes: 104 additions & 1 deletion 105 Modules/_testcapimodule.c

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Original file line number	Diff line number	Diff line change
Expand Up		@@ -3363,7 +3363,7 @@ test_gc_visit_objects_basic(PyObject *Py_UNUSED(self),
		}
		state.target = obj;
		state.found = 0;


		PyUnstable_GC_VisitObjects(gc_visit_callback_basic, &state);
		Py_DECREF(obj);
		if (!state.found) {
Expand Down Expand Up		@@ -3400,6 +3400,98 @@ test_gc_visit_objects_exit_early(PyObject *Py_UNUSED(self),
		Py_RETURN_NONE;
		}

		typedef struct {
		PyObject_HEAD
		} ObjExtraData;

		static PyObject *
		obj_extra_data_new(PyTypeObject type, PyObject args, PyObject *kwds)
		{
		size_t extra_size = sizeof(PyObject *);
		PyObject *obj = PyUnstable_Object_GC_NewWithExtraData(type, extra_size);
		if (obj == NULL) {
		return PyErr_NoMemory();
		}
		PyObject_GC_Track(obj);
		return obj;
		}

		static PyObject **
		obj_extra_data_get_extra_storage(PyObject *self)
		{
		return (PyObject *)((char )self + Py_TYPE(self)->tp_basicsize);
		}

		static PyObject *
		obj_extra_data_get(PyObject self, void Py_UNUSED(ignored))
		{
		PyObject **extra_storage = obj_extra_data_get_extra_storage(self);
		PyObject value = extra_storage;
		if (!value) {
		Py_RETURN_NONE;
		}
		return Py_NewRef(value);
		}

		static int
		obj_extra_data_set(PyObject self, PyObject newval, void *Py_UNUSED(ignored))
		{
		PyObject **extra_storage = obj_extra_data_get_extra_storage(self);
		Py_CLEAR(*extra_storage);
		if (newval) {
		*extra_storage = Py_NewRef(newval);
		}
		return 0;
		}

		static PyGetSetDef obj_extra_data_getset[] = {
		{"extra", (getter)obj_extra_data_get, (setter)obj_extra_data_set, NULL},
		{NULL}
		};

		static int
		obj_extra_data_traverse(PyObject self, visitproc visit, void arg)
		{
		PyObject **extra_storage = obj_extra_data_get_extra_storage(self);
		PyObject value = extra_storage;
		Py_VISIT(value);
		return 0;
		}

		static int
		obj_extra_data_clear(PyObject *self)
		{
		PyObject **extra_storage = obj_extra_data_get_extra_storage(self);
		Py_CLEAR(*extra_storage);
		return 0;
		}

		static void
		obj_extra_data_dealloc(PyObject *self)
		{
		PyTypeObject *tp = Py_TYPE(self);
		PyObject_GC_UnTrack(self);
		obj_extra_data_clear(self);
		tp->tp_free(self);
		Py_DECREF(tp);
		}

		static PyType_Slot ObjExtraData_Slots[] = {
		{Py_tp_getset, obj_extra_data_getset},
		{Py_tp_dealloc, obj_extra_data_dealloc},
		{Py_tp_traverse, obj_extra_data_traverse},
		{Py_tp_clear, obj_extra_data_clear},
		{Py_tp_new, obj_extra_data_new},
		{Py_tp_free, PyObject_GC_Del},
		{0, NULL},
		};

		static PyType_Spec ObjExtraData_TypeSpec = {
		.name = "_testcapi.ObjExtraData",
		.basicsize = sizeof(ObjExtraData),
		.flags = Py_TPFLAGS_DEFAULT \| Py_TPFLAGS_BASETYPE \| Py_TPFLAGS_HAVE_GC,
		.slots = ObjExtraData_Slots,
		};

		struct atexit_data {
		int called;
Expand Down Expand Up		@@ -4124,6 +4216,17 @@ PyInit__testcapi(void)
		Py_INCREF(&MethStatic_Type);
		PyModule_AddObject(m, "MethStatic", (PyObject *)&MethStatic_Type);

		PyObject *ObjExtraData_Type = PyType_FromModuleAndSpec(
		m, &ObjExtraData_TypeSpec, NULL);
		if (ObjExtraData_Type == 0) {
		return NULL;
		}
		int ret = PyModule_AddType(m, (PyTypeObject*)ObjExtraData_Type);
		Py_DECREF(&ObjExtraData_Type);
		if (ret < 0) {
		return NULL;
		}

		PyModule_AddObject(m, "CHAR_MAX", PyLong_FromLong(CHAR_MAX));
		PyModule_AddObject(m, "CHAR_MIN", PyLong_FromLong(CHAR_MIN));
		PyModule_AddObject(m, "UCHAR_MAX", PyLong_FromLong(UCHAR_MAX));
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13 changes: 13 additions & 0 deletions 13 Modules/gcmodule.c

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Original file line number	Diff line number	Diff line change
Expand Up		@@ -2357,6 +2357,19 @@ _PyObject_GC_NewVar(PyTypeObject *tp, Py_ssize_t nitems)
		return op;
		}

		PyObject *
		PyUnstable_Object_GC_NewWithExtraData(PyTypeObject *tp, size_t extra_size)
		{
		size_t presize = _PyType_PreHeaderSize(tp);
		PyObject *op = gc_alloc(_PyObject_SIZE(tp) + extra_size, presize);
		if (op == NULL) {
		return NULL;
		}
		memset(op, 0, _PyObject_SIZE(tp) + extra_size);
		_PyObject_Init(op, tp);
		return op;
		}

		PyVarObject *
		_PyObject_GC_Resize(PyVarObject *op, Py_ssize_t nitems)
		{
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