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Commit 87223f3

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jbradaricencukouerlend-aasland
authored
gh-103743: Add PyUnstable_Object_GC_NewWithExtraData (GH-103744)
 Co-authored-by: Petr Viktorin <encukou@gmail.com> Co-authored-by: Erlend E. Aasland <erlend.aasland@protonmail.com>
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‎Doc/c-api/gcsupport.rst

Copy file name to clipboardExpand all lines: Doc/c-api/gcsupport.rst
+20-1Lines changed: 20 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -59,12 +59,31 @@ rules:
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Analogous to :c:func:`PyObject_New` but for container objects with the
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:const:`Py_TPFLAGS_HAVE_GC` flag set.
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62-
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.. c:function:: TYPE* PyObject_GC_NewVar(TYPE, PyTypeObject *type, Py_ssize_t size)
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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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67+
.. c:function:: PyObject* PyUnstable_Object_GC_NewWithExtraData(PyTypeObject *type, size_t extra_size)
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Analogous to :c:func:`PyObject_GC_New` but allocates *extra_size*
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bytes at the end of the object (at offset
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:c:member:`~PyTypeObject.tp_basicsize`).
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The allocated memory is initialized to zeros,
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except for the :c:type:`Python object header <PyObject>`.
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The extra data will be deallocated with the object, but otherwise it is
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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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For allocating a variable number of fields, prefer using
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:c:type:`PyVarObject` and :c:member:`~PyTypeObject.tp_itemsize`
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instead.
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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/cpython/objimpl.h

Copy file name to clipboardExpand all lines: Include/cpython/objimpl.h
+3Lines changed: 3 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -90,3 +90,6 @@ PyAPI_FUNC(int) PyObject_IS_GC(PyObject *obj);
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PyAPI_FUNC(int) PyType_SUPPORTS_WEAKREFS(PyTypeObject *type);
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9292
PyAPI_FUNC(PyObject **) PyObject_GET_WEAKREFS_LISTPTR(PyObject *op);
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PyAPI_FUNC(PyObject *) PyUnstable_Object_GC_NewWithExtraData(PyTypeObject *,
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size_t);

‎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
10431043
self.assertEqual(_testcapi.function_get_kw_defaults(some), None)
10441044
self.assertEqual(some.__kwdefaults__, None)
10451045

1046+
def test_unstable_gc_new_with_extra_data(self):
1047+
class Data(_testcapi.ObjExtraData):
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__slots__ = ('x', 'y')
1049+
1050+
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)
1059+
10461060

10471061
class TestPendingCalls(unittest.TestCase):
10481062

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

Copy file name to clipboard
+2Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,2 @@
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Add :c:func:`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
+104-1Lines changed: 104 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -3363,7 +3363,7 @@ test_gc_visit_objects_basic(PyObject *Py_UNUSED(self),
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}
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state.target = obj;
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state.found = 0;
3366-
3366+
33673367
PyUnstable_GC_VisitObjects(gc_visit_callback_basic, &state);
33683368
Py_DECREF(obj);
33693369
if (!state.found) {
@@ -3400,6 +3400,98 @@ test_gc_visit_objects_exit_early(PyObject *Py_UNUSED(self),
34003400
Py_RETURN_NONE;
34013401
}
34023402

3403+
typedef struct {
3404+
PyObject_HEAD
3405+
} ObjExtraData;
3406+
3407+
static PyObject *
3408+
obj_extra_data_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
3409+
{
3410+
size_t extra_size = sizeof(PyObject *);
3411+
PyObject *obj = PyUnstable_Object_GC_NewWithExtraData(type, extra_size);
3412+
if (obj == NULL) {
3413+
return PyErr_NoMemory();
3414+
}
3415+
PyObject_GC_Track(obj);
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return obj;
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}
3418+
3419+
static PyObject **
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obj_extra_data_get_extra_storage(PyObject *self)
3421+
{
3422+
return (PyObject **)((char *)self + Py_TYPE(self)->tp_basicsize);
3423+
}
3424+
3425+
static PyObject *
3426+
obj_extra_data_get(PyObject *self, void *Py_UNUSED(ignored))
3427+
{
3428+
PyObject **extra_storage = obj_extra_data_get_extra_storage(self);
3429+
PyObject *value = *extra_storage;
3430+
if (!value) {
3431+
Py_RETURN_NONE;
3432+
}
3433+
return Py_NewRef(value);
3434+
}
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3436+
static int
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obj_extra_data_set(PyObject *self, PyObject *newval, void *Py_UNUSED(ignored))
3438+
{
3439+
PyObject **extra_storage = obj_extra_data_get_extra_storage(self);
3440+
Py_CLEAR(*extra_storage);
3441+
if (newval) {
3442+
*extra_storage = Py_NewRef(newval);
3443+
}
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return 0;
3445+
}
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3447+
static PyGetSetDef obj_extra_data_getset[] = {
3448+
{"extra", (getter)obj_extra_data_get, (setter)obj_extra_data_set, NULL},
3449+
{NULL}
3450+
};
3451+
3452+
static int
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obj_extra_data_traverse(PyObject *self, visitproc visit, void *arg)
3454+
{
3455+
PyObject **extra_storage = obj_extra_data_get_extra_storage(self);
3456+
PyObject *value = *extra_storage;
3457+
Py_VISIT(value);
3458+
return 0;
3459+
}
3460+
3461+
static int
3462+
obj_extra_data_clear(PyObject *self)
3463+
{
3464+
PyObject **extra_storage = obj_extra_data_get_extra_storage(self);
3465+
Py_CLEAR(*extra_storage);
3466+
return 0;
3467+
}
3468+
3469+
static void
3470+
obj_extra_data_dealloc(PyObject *self)
3471+
{
3472+
PyTypeObject *tp = Py_TYPE(self);
3473+
PyObject_GC_UnTrack(self);
3474+
obj_extra_data_clear(self);
3475+
tp->tp_free(self);
3476+
Py_DECREF(tp);
3477+
}
3478+
3479+
static PyType_Slot ObjExtraData_Slots[] = {
3480+
{Py_tp_getset, obj_extra_data_getset},
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{Py_tp_dealloc, obj_extra_data_dealloc},
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{Py_tp_traverse, obj_extra_data_traverse},
3483+
{Py_tp_clear, obj_extra_data_clear},
3484+
{Py_tp_new, obj_extra_data_new},
3485+
{Py_tp_free, PyObject_GC_Del},
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{0, NULL},
3487+
};
3488+
3489+
static PyType_Spec ObjExtraData_TypeSpec = {
3490+
.name = "_testcapi.ObjExtraData",
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.basicsize = sizeof(ObjExtraData),
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.flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE | Py_TPFLAGS_HAVE_GC,
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.slots = ObjExtraData_Slots,
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};
34033495

34043496
struct atexit_data {
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int called;
@@ -4124,6 +4216,17 @@ PyInit__testcapi(void)
41244216
Py_INCREF(&MethStatic_Type);
41254217
PyModule_AddObject(m, "MethStatic", (PyObject *)&MethStatic_Type);
41264218

4219+
PyObject *ObjExtraData_Type = PyType_FromModuleAndSpec(
4220+
m, &ObjExtraData_TypeSpec, NULL);
4221+
if (ObjExtraData_Type == 0) {
4222+
return NULL;
4223+
}
4224+
int ret = PyModule_AddType(m, (PyTypeObject*)ObjExtraData_Type);
4225+
Py_DECREF(&ObjExtraData_Type);
4226+
if (ret < 0) {
4227+
return NULL;
4228+
}
4229+
41274230
PyModule_AddObject(m, "CHAR_MAX", PyLong_FromLong(CHAR_MAX));
41284231
PyModule_AddObject(m, "CHAR_MIN", PyLong_FromLong(CHAR_MIN));
41294232
PyModule_AddObject(m, "UCHAR_MAX", PyLong_FromLong(UCHAR_MAX));

‎Modules/gcmodule.c

Copy file name to clipboardExpand all lines: Modules/gcmodule.c
+13Lines changed: 13 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -2367,6 +2367,19 @@ _PyObject_GC_NewVar(PyTypeObject *tp, Py_ssize_t nitems)
23672367
return op;
23682368
}
23692369

2370+
PyObject *
2371+
PyUnstable_Object_GC_NewWithExtraData(PyTypeObject *tp, size_t extra_size)
2372+
{
2373+
size_t presize = _PyType_PreHeaderSize(tp);
2374+
PyObject *op = gc_alloc(_PyObject_SIZE(tp) + extra_size, presize);
2375+
if (op == NULL) {
2376+
return NULL;
2377+
}
2378+
memset(op, 0, _PyObject_SIZE(tp) + extra_size);
2379+
_PyObject_Init(op, tp);
2380+
return op;
2381+
}
2382+
23702383
PyVarObject *
23712384
_PyObject_GC_Resize(PyVarObject *op, Py_ssize_t nitems)
23722385
{

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