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gh-130313: Avoid locking when clearing objects #130126

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Merged
DinoV merged 3 commits into from
Feb 20, 2025
Merged

gh-130313: Avoid locking when clearing objects #130126

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c00cd86
Avoid locking when clearing objects
DinoV Feb 5, 2025
71ddb72
Small cleanups
DinoV Feb 19, 2025
427cfac
set valid atomically
DinoV Feb 20, 2025
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Small cleanups
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@DinoV
DinoV committed Feb 19, 2025
commit 71ddb723d7eb733af76d0f3e9c07e30b73332b61
107 changes: 57 additions & 50 deletions Objects/dictobject.c
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Original file line number Diff line number Diff line change
Expand Up @@ -7163,6 +7163,17 @@ PyObject_VisitManagedDict(PyObject *obj, visitproc visit, void *arg)
return 0;
}

static void
clear_inline_values(PyDictValues *values)
{
if (values->valid) {
values->valid = 0;

@colesbury colesbury Feb 20, 2025

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Does this need to be FT_ATOMIC_STORE_UINT8(values->valid, 0) for the call from set_dict_inline_values?

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)
{
Expand All @@ -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
Expand Down Expand Up @@ -7338,89 +7344,90 @@ _PyObject_SetManagedDict(PyObject *obj, PyObject *new_dict)
return err;
}

static int
detach_dict_from_object(PyDictObject *mp, PyObject *obj)
{
assert(_PyObject_ManagedDictPointer(obj)->dict == mp);
assert(_PyObject_InlineValuesConsistencyCheck(obj));

if (FT_ATOMIC_LOAD_PTR_RELAXED(mp->ma_values) != _PyObject_InlineValues(obj)) {
return 0;
}

// We could be called with an unlocked dict when the caller knows the
// values are already detached, so we assert after inline values check.
ASSERT_WORLD_STOPPED_OR_OBJ_LOCKED(mp);
assert(mp->ma_values->embedded == 1);
assert(mp->ma_values->valid == 1);
assert(Py_TYPE(obj)->tp_flags & Py_TPFLAGS_INLINE_VALUES);

PyDictValues *values = copy_values(mp->ma_values);

if (values == NULL) {
PyErr_NoMemory();
return -1;
}
mp->ma_values = values;

invalidate_and_clear_inline_values(_PyObject_InlineValues(obj));

assert(_PyObject_InlineValuesConsistencyCheck(obj));
ASSERT_CONSISTENT(mp);
return 0;
}


void
PyObject_ClearManagedDict(PyObject *obj)
{
// This is called when the object is being freed and therefore
// has no other references or during GC when the world is stopped
// so we don't need any locking.
// 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.
PyDictValues *values = _PyObject_InlineValues(obj);
if (values->valid) {
values->valid = 0;
for (Py_ssize_t i = 0; i < values->capacity; i++) {
Py_CLEAR(values->values[i]);
}
}
// No dict to clear, we're done
clear_inline_values(_PyObject_InlineValues(obj));
return;
} else if (FT_ATOMIC_LOAD_PTR_RELAXED(dict->ma_values) ==
}
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 = _PyDict_DetachFromObject(dict, obj);
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");
"clearing an object managed dict");
/* Clear the dict */
Py_BEGIN_CRITICAL_SECTION2(dict, obj);
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);
set_dict_inline_values(obj, NULL);
Py_END_CRITICAL_SECTION2();
clear_inline_values(_PyObject_InlineValues(obj));
Py_END_CRITICAL_SECTION();
}
}
// Else we have a materialized dict which doesn't point at the inline
// values, we can just clear it.
}
Py_CLEAR(_PyObject_ManagedDictPointer(obj)->dict);
}

int
_PyDict_DetachFromObject(PyDictObject *mp, PyObject *obj)
{
assert(_PyObject_ManagedDictPointer(obj)->dict == mp);
assert(_PyObject_InlineValuesConsistencyCheck(obj));

if (FT_ATOMIC_LOAD_PTR_RELAXED(mp->ma_values) != _PyObject_InlineValues(obj)) {
return 0;
}

// We could be called with an unlocked dict when the caller knows the
// values are already detached, so we assert after inline values check.
ASSERT_WORLD_STOPPED_OR_OBJ_LOCKED(mp);
assert(mp->ma_values->embedded == 1);
assert(mp->ma_values->valid == 1);
assert(Py_TYPE(obj)->tp_flags & Py_TPFLAGS_INLINE_VALUES);

PyDictValues *values = copy_values(mp->ma_values);

if (values == NULL) {
PyErr_NoMemory();
return -1;
}
mp->ma_values = values;

invalidate_and_clear_inline_values(_PyObject_InlineValues(obj));
ASSERT_WORLD_STOPPED_OR_OBJ_LOCKED(obj);

assert(_PyObject_InlineValuesConsistencyCheck(obj));
ASSERT_CONSISTENT(mp);
return 0;
return detach_dict_from_object(mp, obj);
}

static inline PyObject *
Expand Down