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Merged
vstinner merged 11 commits into from
May 28, 2021
+37 −22
Merged

bpo-42972: Fully implement GC protocol for functools keywrapper and partial types #26363

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8ef6e98
bpo-42972: Fully implement GC protocol for functools types
May 25, 2021
6d7cdaf
Address review
May 26, 2021
a15b49f
Address review: visit node type for each strong ref
May 27, 2021
0c8df1f
Address review: visit members in correct order
May 27, 2021
f9ac4c5
Address review: revert Py_CLEAR change in lru_list_elem_dealloc
May 27, 2021
fc39917
Revert LRU cache element optimisation
May 27, 2021
07f2182
Address review: revert redundant slot removal
May 27, 2021
0861788
Address review: use tp_free
May 27, 2021
7c2f750
Revert lru list elem clear fn
May 27, 2021
6313247
Revert "Revert LRU cache element optimisation"
May 28, 2021
1539195
Restore lru_cache_tp_traverse
May 28, 2021
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84 changes: 56 additions & 28 deletions Modules/_functoolsmodule.c
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Original file line number Diff line number Diff line change
Expand Up @@ -147,18 +147,37 @@ partial_new(PyTypeObject *type, PyObject *args, PyObject *kw)
return (PyObject *)pto;
}

static int
partial_clear(partialobject *pto)
{
Py_CLEAR(pto->fn);
Py_CLEAR(pto->args);
Py_CLEAR(pto->kw);
Py_CLEAR(pto->dict);
return 0;
}

static int
partial_traverse(partialobject *pto, visitproc visit, void *arg)
{
Py_VISIT(Py_TYPE(pto));
Py_VISIT(pto->fn);
Py_VISIT(pto->args);
Py_VISIT(pto->kw);
Py_VISIT(pto->dict);
return 0;
}

static void
partial_dealloc(partialobject *pto)
{
PyTypeObject *tp = Py_TYPE(pto);
/* bpo-31095: UnTrack is needed before calling any callbacks */
PyObject_GC_UnTrack(pto);
if (pto->weakreflist != NULL)
if (pto->weakreflist != NULL) {
PyObject_ClearWeakRefs((PyObject *) pto);
Py_XDECREF(pto->fn);
Py_XDECREF(pto->args);
Py_XDECREF(pto->kw);
Py_XDECREF(pto->dict);
}
(void)partial_clear(pto);
tp->tp_free(pto);
Py_DECREF(tp);
}
Expand Down Expand Up @@ -307,16 +326,6 @@ partial_call(partialobject *pto, PyObject *args, PyObject *kwargs)
return res;
}

static int
partial_traverse(partialobject *pto, visitproc visit, void *arg)
{
Py_VISIT(pto->fn);
Py_VISIT(pto->args);
Py_VISIT(pto->kw);
Py_VISIT(pto->dict);
return 0;
}

PyDoc_STRVAR(partial_doc,
"partial(func, *args, **keywords) - new function with partial application\n\
of the given arguments and keywords.\n");
Expand Down Expand Up @@ -469,6 +478,7 @@ static PyType_Slot partial_type_slots[] = {
{Py_tp_setattro, PyObject_GenericSetAttr},
{Py_tp_doc, (void *)partial_doc},
{Py_tp_traverse, partial_traverse},
{Py_tp_clear, partial_clear},
{Py_tp_methods, partial_methods},
{Py_tp_members, partial_memberlist},
{Py_tp_getset, partial_getsetlist},
Expand Down Expand Up @@ -506,14 +516,16 @@ static void
keyobject_dealloc(keyobject *ko)
{
PyTypeObject *tp = Py_TYPE(ko);
keyobject_clear(ko);
PyObject_Free(ko);
PyObject_GC_UnTrack(ko);
(void)keyobject_clear(ko);
tp->tp_free(ko);
Py_DECREF(tp);
}

static int
keyobject_traverse(keyobject *ko, visitproc visit, void *arg)
{
Py_VISIT(Py_TYPE(ko));
Py_VISIT(ko->cmp);
Py_VISIT(ko->object);
return 0;
Expand Down Expand Up @@ -546,7 +558,8 @@ static PyType_Slot keyobject_type_slots[] = {
static PyType_Spec keyobject_type_spec = {
.name = "functools.KeyWrapper",
.basicsize = sizeof(keyobject),
.flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_DISALLOW_INSTANTIATION,
.flags = (Py_TPFLAGS_DEFAULT | Py_TPFLAGS_DISALLOW_INSTANTIATION |
Py_TPFLAGS_HAVE_GC),
.slots = keyobject_type_slots
};

Expand All @@ -560,14 +573,15 @@ keyobject_call(keyobject *ko, PyObject *args, PyObject *kwds)
if (!PyArg_ParseTupleAndKeywords(args, kwds, "O:K", kwargs, &object))
return NULL;

result = PyObject_New(keyobject, Py_TYPE(ko));
result = PyObject_GC_New(keyobject, Py_TYPE(ko));
if (result == NULL) {
return NULL;
}
Py_INCREF(ko->cmp);
result->cmp = ko->cmp;
Py_INCREF(object);
result->object = object;
PyObject_GC_Track(result);
return (PyObject *)result;
}

Expand Down Expand Up @@ -621,12 +635,13 @@ functools_cmp_to_key(PyObject *self, PyObject *args, PyObject *kwds)
return NULL;

state = get_functools_state(self);
object = PyObject_New(keyobject, state->keyobject_type);
object = PyObject_GC_New(keyobject, state->keyobject_type);
if (!object)
return NULL;
Py_INCREF(cmp);
object->cmp = cmp;
object->object = NULL;
PyObject_GC_Track(object);
return (PyObject *)object;
}

Expand Down Expand Up @@ -748,25 +763,37 @@ typedef struct lru_list_elem {
PyObject *key, *result;
} lru_list_elem;

static int
lru_list_elem_traverse(lru_list_elem *link, visitproc visit, void *arg)
{
Py_VISIT(link->key);
Py_VISIT(link->result);
Py_VISIT(Py_TYPE(link));
return 0;
}
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@vstinner vstinner May 27, 2021

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A lru_list_elem_clear() function would also be needed to implement the GC protocol, no?

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@erlend-aasland erlend-aasland May 27, 2021

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A lru_list_elem_clear() function would also be needed to implement the GC protocol, no?

I was under the impression traverse was enough. I may be wrong.

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@vstinner vstinner May 27, 2021

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Without clear, the ref count cannot each zero, and the GC cannot break cycles: https://devguide.python.org/garbage_collector/#destroying-unreachable-objects

cc @pablogsal

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@methane methane May 28, 2021

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_lru_list_elem is not a standalone type. It is an internal of _lru_cache_wrapper.

  • lru_cache_tp_traverse() visits lru_list_elem.
  • lru_cache_tp_clear() clears lru_list_elem.

That's why we can keep _lru_list_elem non-GC type.

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@shihai1991 shihai1991 May 28, 2021

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IMO, Inada's #26416 is acceptable.


static void
lru_list_elem_dealloc(lru_list_elem *link)
{
PyTypeObject *tp = Py_TYPE(link);
PyObject_GC_UnTrack(link);
Py_XDECREF(link->key);
Py_XDECREF(link->result);
PyObject_Free(link);
tp->tp_free(link);
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Py_DECREF(tp);
}

static PyType_Slot lru_list_elem_type_slots[] = {
{Py_tp_dealloc, lru_list_elem_dealloc},
{Py_tp_traverse, lru_list_elem_traverse},
{0, 0}
};

static PyType_Spec lru_list_elem_type_spec = {
.name = "functools._lru_list_elem",
.basicsize = sizeof(lru_list_elem),
.flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_DISALLOW_INSTANTIATION,
.flags = (Py_TPFLAGS_DEFAULT | Py_TPFLAGS_DISALLOW_INSTANTIATION |
Py_TPFLAGS_HAVE_GC),
.slots = lru_list_elem_type_slots
};

Expand Down Expand Up @@ -1031,8 +1058,8 @@ bounded_lru_cache_wrapper(lru_cache_object *self, PyObject *args, PyObject *kwds
self->root.next == &self->root)
{
/* Cache is not full, so put the result in a new link */
link = (lru_list_elem *)PyObject_New(lru_list_elem,
self->lru_list_elem_type);
link = (lru_list_elem *)PyObject_GC_New(lru_list_elem,
self->lru_list_elem_type);
if (link == NULL) {
Py_DECREF(key);
Py_DECREF(result);
Expand All @@ -1042,6 +1069,7 @@ bounded_lru_cache_wrapper(lru_cache_object *self, PyObject *args, PyObject *kwds
link->hash = hash;
link->key = key;
link->result = result;
PyObject_GC_Track(link);
/* What is really needed here is a SetItem variant with a "no clobber"
option. If the __eq__ call triggers a reentrant call that adds
this same key, then this setitem call will update the cache dict
Expand Down Expand Up @@ -1260,7 +1288,7 @@ lru_cache_dealloc(lru_cache_object *obj)
PyObject_ClearWeakRefs((PyObject*)obj);
}

lru_cache_tp_clear(obj);
(void)lru_cache_tp_clear(obj);
tp->tp_free(obj);
Py_DECREF(tp);
}
Expand Down Expand Up @@ -1327,15 +1355,15 @@ lru_cache_deepcopy(PyObject *self, PyObject *unused)
static int
lru_cache_tp_traverse(lru_cache_object *self, visitproc visit, void *arg)
{
Py_VISIT(Py_TYPE(self));
lru_list_elem *link = self->root.next;
while (link != &self->root) {
lru_list_elem *next = link->next;
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Py_VISIT(link->key);
Py_VISIT(link->result);
Py_VISIT(link);
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Outdated
link = next;
}
Py_VISIT(self->func);
Py_VISIT(self->cache);
Py_VISIT(self->func);
Py_VISIT(self->kwd_mark);
Py_VISIT(self->lru_list_elem_type);
Py_VISIT(self->cache_info_type);
Expand Down