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gh-130313: Avoid locking when clearing objects (#130126)

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Avoid locking when clearing objects in the free-threaded build
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Dino Viehland 2025-02-20 13:32:57 -08:00 • committed by GitHub
parent 69426fcee7
commit 6c450f44c2
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GPG key ID: B5690EEEBB952194
1 changed files with 73 additions and 44 deletions
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117
Objects/dictobject.c
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@ -7163,6 +7163,17 @@ PyObject_VisitManagedDict(PyObject *obj, visitproc visit, void *arg)
return 0;
}
static void
clear_inline_values(PyDictValues *values)
{
if (values->valid) {
FT_ATOMIC_STORE_UINT8(values->valid, 0);
for (Py_ssize_t i = 0; i < values->capacity; i++) {
Py_CLEAR(values->values[i]);
}
}
}
static void
set_dict_inline_values(PyObject *obj, PyDictObject *new_dict)
{
@ -7173,12 +7184,7 @@ set_dict_inline_values(PyObject *obj, PyDictObject *new_dict)
Py_XINCREF(new_dict);
FT_ATOMIC_STORE_PTR(_PyObject_ManagedDictPointer(obj)->dict, new_dict);
if (values->valid) {
FT_ATOMIC_STORE_UINT8(values->valid, 0);
for (Py_ssize_t i = 0; i < values->capacity; i++) {
Py_CLEAR(values->values[i]);
}
}
clear_inline_values(values);
}
#ifdef Py_GIL_DISABLED
@ -7256,8 +7262,8 @@ decref_maybe_delay(PyObject *obj, bool delay)
}
}
static int
set_or_clear_managed_dict(PyObject *obj, PyObject *new_dict, bool clear)
int
_PyObject_SetManagedDict(PyObject *obj, PyObject *new_dict)
{
assert(Py_TYPE(obj)->tp_flags & Py_TPFLAGS_MANAGED_DICT);
#ifndef NDEBUG
@ -7292,8 +7298,7 @@ set_or_clear_managed_dict(PyObject *obj, PyObject *new_dict, bool clear)
// Decref for the dictionary we incref'd in try_set_dict_inline_only_or_other_dict
// while the object was locked
decref_maybe_delay((PyObject *)prev_dict,
!clear && prev_dict != cur_dict);
decref_maybe_delay((PyObject *)prev_dict, prev_dict != cur_dict);
if (err != 0) {
return err;
}
@ -7303,7 +7308,7 @@ set_or_clear_managed_dict(PyObject *obj, PyObject *new_dict, bool clear)
if (prev_dict != NULL) {
// decref for the dictionary that we replaced
decref_maybe_delay((PyObject *)prev_dict, !clear);
decref_maybe_delay((PyObject *)prev_dict, true);
}
return 0;
@ -7333,45 +7338,15 @@ set_or_clear_managed_dict(PyObject *obj, PyObject *new_dict, bool clear)
(PyDictObject *)Py_XNewRef(new_dict));
Py_END_CRITICAL_SECTION();
decref_maybe_delay((PyObject *)dict, !clear);
decref_maybe_delay((PyObject *)dict, true);
}
assert(_PyObject_InlineValuesConsistencyCheck(obj));
return err;
}
int
_PyObject_SetManagedDict(PyObject *obj, PyObject *new_dict)
static int
detach_dict_from_object(PyDictObject *mp, PyObject *obj)
{
return set_or_clear_managed_dict(obj, new_dict, false);
}
void
PyObject_ClearManagedDict(PyObject *obj)
{
if (set_or_clear_managed_dict(obj, NULL, true) < 0) {
/* Must be out of memory */
assert(PyErr_Occurred() == PyExc_MemoryError);
PyErr_FormatUnraisable("Exception ignored while "
"clearing an object managed dict");
/* Clear the dict */
PyDictObject *dict = _PyObject_GetManagedDict(obj);
Py_BEGIN_CRITICAL_SECTION2(dict, obj);
dict = _PyObject_ManagedDictPointer(obj)->dict;
PyInterpreterState *interp = _PyInterpreterState_GET();
PyDictKeysObject *oldkeys = dict->ma_keys;
set_keys(dict, Py_EMPTY_KEYS);
dict->ma_values = NULL;
dictkeys_decref(interp, oldkeys, IS_DICT_SHARED(dict));
STORE_USED(dict, 0);
set_dict_inline_values(obj, NULL);
Py_END_CRITICAL_SECTION2();
}
}
int
_PyDict_DetachFromObject(PyDictObject *mp, PyObject *obj)
{
ASSERT_WORLD_STOPPED_OR_OBJ_LOCKED(obj);
assert(_PyObject_ManagedDictPointer(obj)->dict == mp);
assert(_PyObject_InlineValuesConsistencyCheck(obj));
@ -7401,6 +7376,60 @@ _PyDict_DetachFromObject(PyDictObject *mp, PyObject *obj)
return 0;
}
void
PyObject_ClearManagedDict(PyObject *obj)
{
// This is called when the object is being freed or cleared
// by the GC and therefore known to have no references.
if (Py_TYPE(obj)->tp_flags & Py_TPFLAGS_INLINE_VALUES) {
PyDictObject *dict = _PyObject_GetManagedDict(obj);
if (dict == NULL) {
// We have no materialized dictionary and inline values
// that just need to be cleared.
// No dict to clear, we're done
clear_inline_values(_PyObject_InlineValues(obj));
return;
}
else if (FT_ATOMIC_LOAD_PTR_RELAXED(dict->ma_values) ==
_PyObject_InlineValues(obj)) {
// We have a materialized object which points at the inline
// values. We need to materialize the keys. Nothing can modify
// this object, but we need to lock the dictionary.
int err;
Py_BEGIN_CRITICAL_SECTION(dict);
err = detach_dict_from_object(dict, obj);
Py_END_CRITICAL_SECTION();
if (err) {
/* Must be out of memory */
assert(PyErr_Occurred() == PyExc_MemoryError);
PyErr_FormatUnraisable("Exception ignored while "
"clearing an object managed dict");
/* Clear the dict */
Py_BEGIN_CRITICAL_SECTION(dict);
PyInterpreterState *interp = _PyInterpreterState_GET();
PyDictKeysObject *oldkeys = dict->ma_keys;
set_keys(dict, Py_EMPTY_KEYS);
dict->ma_values = NULL;
dictkeys_decref(interp, oldkeys, IS_DICT_SHARED(dict));
STORE_USED(dict, 0);
clear_inline_values(_PyObject_InlineValues(obj));
Py_END_CRITICAL_SECTION();
}
}
}
Py_CLEAR(_PyObject_ManagedDictPointer(obj)->dict);
}
int
_PyDict_DetachFromObject(PyDictObject *mp, PyObject *obj)
{
ASSERT_WORLD_STOPPED_OR_OBJ_LOCKED(obj);
return detach_dict_from_object(mp, obj);
}
static inline PyObject *
ensure_managed_dict(PyObject *obj)
{