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Commit cc46476

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jbradaricjbradaric
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gh-103743: Add PyUnstable_Object_GC_NewWithExtraData (#103743)
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‎Doc/c-api/gcsupport.rst

Copy file name to clipboardExpand all lines: Doc/c-api/gcsupport.rst
+13Lines changed: 13 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -65,6 +65,19 @@ rules:
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Analogous to :c:func:`PyObject_NewVar` but for container objects with the
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:const:`Py_TPFLAGS_HAVE_GC` flag set.
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.. c:function:: TYPE* PyUnstable_Object_GC_NewWithExtraData(PyTypeObject *type, size_t extra_size)
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Analogous to :c:func:`PyObject_GC_New` but for container objects that
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have additional data at the end of the object not managed by Python.
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.. warning::
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The function is marked as unstable because the final mechanism
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for reserving extra data after an instance is not yet decided.
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Once :pep:`697` is implemented, the mechanism described there can
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be used to reserve the extra data.
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.. versionadded:: 3.12
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.. c:function:: TYPE* PyObject_GC_Resize(TYPE, PyVarObject *op, Py_ssize_t newsize)
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‎Include/objimpl.h

Copy file name to clipboardExpand all lines: Include/objimpl.h
+4Lines changed: 4 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -131,6 +131,10 @@ PyAPI_FUNC(PyVarObject *) PyObject_InitVar(PyVarObject *,
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PyAPI_FUNC(PyObject *) _PyObject_New(PyTypeObject *);
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PyAPI_FUNC(PyVarObject *) _PyObject_NewVar(PyTypeObject *, Py_ssize_t);
133133

134+
#if !defined(Py_LIMITED_API)
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PyAPI_FUNC(PyObject *) PyUnstable_Object_GC_NewWithExtraData(PyTypeObject *, size_t);
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#endif
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#define PyObject_New(type, typeobj) ((type *)_PyObject_New(typeobj))
135139

136140
// Alias to PyObject_New(). In Python 3.8, PyObject_NEW() called directly

‎Lib/test/test_capi/test_misc.py

Copy file name to clipboardExpand all lines: Lib/test/test_capi/test_misc.py
+14Lines changed: 14 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1043,6 +1043,20 @@ class dictsub(dict): ... # dict subclasses must work
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self.assertEqual(_testcapi.function_get_kw_defaults(some), None)
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self.assertEqual(some.__kwdefaults__, None)
10451045

1046+
def test_unstable_gc_new_with_extra_data(self):
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class Data(_testcapi.ObjExtraData):
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__slots__ = ('x', 'y')
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d = Data()
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d.x = 10
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d.y = 20
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d.extra = 30
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self.assertEqual(d.x, 10)
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self.assertEqual(d.y, 20)
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self.assertEqual(d.extra, 30)
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del d.extra
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self.assertIsNone(d.extra)
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10461060

10471061
class TestPendingCalls(unittest.TestCase):
10481062

‎Misc/NEWS.d/next/C API/2023-04-24-10-31-59.gh-issue-103743.2xYA1K.rst

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+2Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,2 @@
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Add ``PyUnstable_Object_GC_NewWithExtraData`` function that can be used to
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allocate additional memory after an object for data not managed by Python.

‎Modules/_testcapimodule.c

Copy file name to clipboardExpand all lines: Modules/_testcapimodule.c
+95-1Lines changed: 95 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -3343,7 +3343,7 @@ test_gc_visit_objects_basic(PyObject *Py_UNUSED(self),
33433343
}
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state.target = obj;
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state.found = 0;
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33473347
PyUnstable_GC_VisitObjects(gc_visit_callback_basic, &state);
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Py_DECREF(obj);
33493349
if (!state.found) {
@@ -3380,6 +3380,95 @@ test_gc_visit_objects_exit_early(PyObject *Py_UNUSED(self),
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Py_RETURN_NONE;
33813381
}
33823382

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typedef struct {
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PyObject_HEAD
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} ObjExtraData;
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static PyObject *
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obj_extra_data_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
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{
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size_t extra_size = sizeof(PyObject *);
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PyObject *obj = PyUnstable_Object_GC_NewWithExtraData(type, extra_size);
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if (obj == NULL)
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return PyErr_NoMemory();
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memset(obj, '\0', type->tp_basicsize + extra_size);
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PyObject_Init(obj, type);
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PyObject_GC_Track(obj);
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return obj;
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}
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static PyObject **
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obj_extra_data_get_extra_storage(PyObject *self)
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{
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return (PyObject **)((char *)self + Py_TYPE(self)->tp_basicsize);
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}
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static PyObject *
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obj_extra_data_get(PyObject *self, void *Py_UNUSED(ignored))
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{
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PyObject **extra_storage = obj_extra_data_get_extra_storage(self);
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PyObject *value = *extra_storage;
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if (!value)
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Py_RETURN_NONE;
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Py_INCREF(value);
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return value;
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}
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static int
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obj_extra_data_set(PyObject *self, PyObject *newval, void *Py_UNUSED(ignored))
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{
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PyObject **extra_storage = obj_extra_data_get_extra_storage(self);
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Py_CLEAR(*extra_storage);
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if (newval) {
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Py_INCREF(newval);
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*extra_storage = newval;
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}
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return 0;
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}
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static PyGetSetDef obj_extra_data_getset[] = {
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{"extra", (getter)obj_extra_data_get, (setter)obj_extra_data_set, NULL},
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{NULL}
3432+
};
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static int
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obj_extra_data_traverse(PyObject *self, visitproc visit, void *arg)
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{
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PyObject **extra_storage = obj_extra_data_get_extra_storage(self);
3438+
PyObject *value = *extra_storage;
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Py_VISIT(value);
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return 0;
3441+
}
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3443+
static int
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obj_extra_data_clear(PyObject *self)
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{
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PyObject **extra_storage = obj_extra_data_get_extra_storage(self);
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Py_CLEAR(*extra_storage);
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return 0;
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}
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static void
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obj_extra_data_dealloc(PyObject *self)
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{
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PyObject_GC_UnTrack(self);
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obj_extra_data_clear(self);
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Py_TYPE(self)->tp_free(self);
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}
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static PyTypeObject ObjExtraData_Type = {
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PyVarObject_HEAD_INIT(NULL, 0)
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"obj_with_extra_data",
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sizeof(ObjExtraData),
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0,
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.tp_getset = obj_extra_data_getset,
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.tp_dealloc = obj_extra_data_dealloc,
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.tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE | Py_TPFLAGS_HAVE_GC,
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.tp_traverse = (traverseproc)obj_extra_data_traverse,
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.tp_clear = (inquiry)obj_extra_data_clear,
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.tp_new = obj_extra_data_new,
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.tp_free = PyObject_GC_Del,
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};
33833472

33843473
struct atexit_data {
33853474
int called;
@@ -4103,6 +4192,11 @@ PyInit__testcapi(void)
41034192
Py_INCREF(&MethStatic_Type);
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PyModule_AddObject(m, "MethStatic", (PyObject *)&MethStatic_Type);
41054194

4195+
if (PyType_Ready(&ObjExtraData_Type) < 0)
4196+
return NULL;
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Py_INCREF(&ObjExtraData_Type);
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PyModule_AddObject(m, "ObjExtraData", (PyObject *)&ObjExtraData_Type);
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41064200
PyModule_AddObject(m, "CHAR_MAX", PyLong_FromLong(CHAR_MAX));
41074201
PyModule_AddObject(m, "CHAR_MIN", PyLong_FromLong(CHAR_MIN));
41084202
PyModule_AddObject(m, "UCHAR_MAX", PyLong_FromLong(UCHAR_MAX));

‎Modules/gcmodule.c

Copy file name to clipboardExpand all lines: Modules/gcmodule.c
+12Lines changed: 12 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -2357,6 +2357,18 @@ _PyObject_GC_NewVar(PyTypeObject *tp, Py_ssize_t nitems)
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return op;
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}
23592359

2360+
PyObject *
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PyUnstable_Object_GC_NewWithExtraData(PyTypeObject *tp, size_t extra_size)
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{
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size_t presize = _PyType_PreHeaderSize(tp);
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PyObject *op = gc_alloc(_PyObject_SIZE(tp) + extra_size, presize);
2365+
if (op == NULL) {
2366+
return NULL;
2367+
}
2368+
_PyObject_Init(op, tp);
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return op;
2370+
}
2371+
23602372
PyVarObject *
23612373
_PyObject_GC_Resize(PyVarObject *op, Py_ssize_t nitems)
23622374
{

‎Tools/c-analyzer/cpython/ignored.tsv

Copy file name to clipboardExpand all lines: Tools/c-analyzer/cpython/ignored.tsv
+1Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -508,6 +508,7 @@ Modules/_testcapimodule.c - g_dict_watch_events -
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Modules/_testcapimodule.c - g_dict_watchers_installed -
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Modules/_testcapimodule.c - g_type_modified_events -
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Modules/_testcapimodule.c - g_type_watchers_installed -
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Modules/_testcapimodule.c - ObjExtraData_Type -
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Modules/_testimportmultiple.c - _barmodule -
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Modules/_testimportmultiple.c - _foomodule -
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Modules/_testimportmultiple.c - _testimportmultiple -

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