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gh-141510: Add can_modify_dict() in dictobject.c #144955

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Merged
vstinner merged 1 commit into from
Feb 18, 2026
+55 −47
Merged

gh-141510: Add can_modify_dict() in dictobject.c #144955

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102 changes: 55 additions & 47 deletions Objects/dictobject.c
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Original file line number Diff line number Diff line change
Expand Up @@ -282,6 +282,24 @@ load_keys_nentries(PyDictObject *mp)

#endif

#ifndef NDEBUG
// Check if it's possible to modify a dictionary.
// Usage: assert(can_modify_dict(mp)).
static inline int
can_modify_dict(PyDictObject *mp)
{
if (PyFrozenDict_Check(mp)) {
// No locking required to modify a newly created frozendict
// since it's only accessible from the current thread.
return PyUnstable_Object_IsUniquelyReferenced(_PyObject_CAST(mp));
}
else {
ASSERT_DICT_LOCKED(mp);
return 1;
}
}
#endif

#define _PyAnyDict_CAST(op) \
(assert(PyAnyDict_Check(op)), _Py_CAST(PyDictObject*, op))

Expand Down Expand Up @@ -1867,8 +1885,9 @@ insert_split_key(PyDictKeysObject *keys, PyObject *key, Py_hash_t hash)
static void
insert_split_value(PyDictObject *mp, PyObject *key, PyObject *value, Py_ssize_t ix)
{
assert(can_modify_dict(mp));
assert(PyUnicode_CheckExact(key));
ASSERT_DICT_LOCKED(mp);

PyObject *old_value = mp->ma_values->values[ix];
if (old_value == NULL) {
_PyDict_NotifyEvent(PyDict_EVENT_ADDED, mp, key, value);
Expand Down Expand Up @@ -1896,11 +1915,11 @@ static int
insertdict(PyDictObject *mp,
PyObject *key, Py_hash_t hash, PyObject *value)
{
assert(can_modify_dict(mp));

PyObject *old_value = NULL;
Py_ssize_t ix;

ASSERT_DICT_LOCKED(mp);

if (_PyDict_HasSplitTable(mp) && PyUnicode_CheckExact(key)) {
ix = insert_split_key(mp->ma_keys, key, hash);
if (ix != DKIX_EMPTY) {
Expand Down Expand Up @@ -1967,8 +1986,8 @@ static int
insert_to_emptydict(PyDictObject *mp,
PyObject *key, Py_hash_t hash, PyObject *value)
{
assert(can_modify_dict(mp));
assert(mp->ma_keys == Py_EMPTY_KEYS);
ASSERT_DICT_LOCKED(mp);

int unicode = PyUnicode_CheckExact(key);
PyDictKeysObject *newkeys = new_keys_object(PyDict_LOG_MINSIZE, unicode);
Expand Down Expand Up @@ -2069,11 +2088,11 @@ static int
dictresize(PyDictObject *mp,
uint8_t log2_newsize, int unicode)
{
assert(can_modify_dict(mp));

PyDictKeysObject *oldkeys, *newkeys;
PyDictValues *oldvalues;

ASSERT_DICT_LOCKED(mp);

if (log2_newsize >= SIZEOF_SIZE_T*8) {
PyErr_NoMemory();
return -1;
Expand Down Expand Up @@ -2671,11 +2690,13 @@ _PyDict_LoadBuiltinsFromGlobals(PyObject *globals)

/* Consumes references to key and value */
static int
anydict_setitem_take2(PyDictObject *mp, PyObject *key, PyObject *value)
setitem_take2_lock_held(PyDictObject *mp, PyObject *key, PyObject *value)
{
assert(PyAnyDict_Check(mp));
assert(can_modify_dict(mp));
assert(key);
assert(value);
assert(PyAnyDict_Check(mp));

Py_hash_t hash = _PyObject_HashFast(key);
if (hash == -1) {
dict_unhashable_type(key);
Expand All @@ -2691,14 +2712,6 @@ anydict_setitem_take2(PyDictObject *mp, PyObject *key, PyObject *value)
return insertdict(mp, key, hash, value);
}

/* Consumes references to key and value */
static int
setitem_take2_lock_held(PyDictObject *mp, PyObject *key, PyObject *value)
{
ASSERT_DICT_LOCKED(mp);
return anydict_setitem_take2(mp, key, value);
}

int
_PyDict_SetItem_Take2(PyDictObject *mp, PyObject *key, PyObject *value)
{
Expand Down Expand Up @@ -2800,9 +2813,9 @@ static void
delitem_common(PyDictObject *mp, Py_hash_t hash, Py_ssize_t ix,
PyObject *old_value)
{
PyObject *old_key;
assert(can_modify_dict(mp));

ASSERT_DICT_LOCKED(mp);
PyObject *old_key;

Py_ssize_t hashpos = lookdict_index(mp->ma_keys, hash, ix);
assert(hashpos >= 0);
Expand Down Expand Up @@ -2856,19 +2869,17 @@ int
_PyDict_DelItem_KnownHash_LockHeld(PyObject *op, PyObject *key, Py_hash_t hash)
{
Py_ssize_t ix;
PyDictObject *mp;
PyObject *old_value;

if (!PyDict_Check(op)) {
PyErr_BadInternalCall();
return -1;
}

ASSERT_DICT_LOCKED(op);
PyDictObject *mp = (PyDictObject *)op;
assert(can_modify_dict(mp));

assert(key);
assert(hash != -1);
mp = (PyDictObject *)op;
ix = _Py_dict_lookup(mp, key, hash, &old_value);
if (ix == DKIX_ERROR)
return -1;
Expand Down Expand Up @@ -2897,19 +2908,18 @@ delitemif_lock_held(PyObject *op, PyObject *key,
int (*predicate)(PyObject *value, void *arg),
void *arg)
{
PyDictObject *mp = _PyAnyDict_CAST(op);
assert(can_modify_dict(mp));

Py_ssize_t ix;
PyDictObject *mp;
Py_hash_t hash;
PyObject *old_value;
int res;

ASSERT_DICT_LOCKED(op);

assert(key);
hash = PyObject_Hash(key);
if (hash == -1)
return -1;
mp = (PyDictObject *)op;
ix = _Py_dict_lookup(mp, key, hash, &old_value);
if (ix == DKIX_ERROR) {
return -1;
Expand Down Expand Up @@ -2951,16 +2961,16 @@ _PyDict_DelItemIf(PyObject *op, PyObject *key,
static void
clear_lock_held(PyObject *op)
{
PyDictObject *mp;
if (!PyDict_Check(op)) {
return;
}
PyDictObject *mp = (PyDictObject *)op;
assert(can_modify_dict(mp));

PyDictKeysObject *oldkeys;
PyDictValues *oldvalues;
Py_ssize_t i, n;

ASSERT_DICT_LOCKED(op);

if (!PyDict_Check(op))
return;
mp = ((PyDictObject *)op);
oldkeys = mp->ma_keys;
oldvalues = mp->ma_values;
if (oldkeys == Py_EMPTY_KEYS) {
Expand Down Expand Up @@ -3106,8 +3116,7 @@ _PyDict_Pop_KnownHash(PyDictObject *mp, PyObject *key, Py_hash_t hash,
PyObject **result)
{
assert(PyDict_Check(mp));

ASSERT_DICT_LOCKED(mp);
assert(can_modify_dict(mp));

if (mp->ma_used == 0) {
if (result) {
Expand Down Expand Up @@ -3149,8 +3158,6 @@ _PyDict_Pop_KnownHash(PyDictObject *mp, PyObject *key, Py_hash_t hash,
static int
pop_lock_held(PyObject *op, PyObject *key, PyObject **result)
{
ASSERT_DICT_LOCKED(op);

if (!PyDict_Check(op)) {
if (result) {
*result = NULL;
Expand All @@ -3159,6 +3166,7 @@ pop_lock_held(PyObject *op, PyObject *key, PyObject **result)
return -1;
}
PyDictObject *dict = (PyDictObject *)op;
assert(can_modify_dict(dict));

if (dict->ma_used == 0) {
if (result) {
Expand Down Expand Up @@ -3361,9 +3369,9 @@ dict_iter_exit:;
}
else if (PyFrozenDict_CheckExact(d)) {
while ((key = PyIter_Next(it)) != NULL) {
// anydict_setitem_take2 consumes a reference to key
status = anydict_setitem_take2((PyDictObject *)d,
key, Py_NewRef(value));
// setitem_take2_lock_held consumes a reference to key
status = setitem_take2_lock_held((PyDictObject *)d,
key, Py_NewRef(value));
if (status < 0) {
assert(PyErr_Occurred());
goto Fail;
Expand Down Expand Up @@ -3933,7 +3941,7 @@ PyDict_MergeFromSeq2(PyObject *d, PyObject *seq2, int override)
static int
dict_dict_merge(PyDictObject *mp, PyDictObject *other, int override)
{
ASSERT_DICT_LOCKED(mp);
assert(can_modify_dict(mp));
ASSERT_DICT_LOCKED(other);

if (other == mp || other->ma_used == 0)
Expand Down Expand Up @@ -4474,15 +4482,14 @@ dict_setdefault_ref_lock_held(PyObject *d, PyObject *key, PyObject *default_valu
Py_hash_t hash;
Py_ssize_t ix;

ASSERT_DICT_LOCKED(d);

if (!PyDict_Check(d)) {
PyErr_BadInternalCall();
if (result) {
*result = NULL;
}
return -1;
}
assert(can_modify_dict((PyDictObject*)d));

hash = _PyObject_HashFast(key);
if (hash == -1) {
Expand Down Expand Up @@ -4657,11 +4664,11 @@ static PyObject *
dict_popitem_impl(PyDictObject *self)
/*[clinic end generated code: output=e65fcb04420d230d input=ef28b4da5f0f762e]*/
{
assert(can_modify_dict(self));

Py_ssize_t i, j;
PyObject *res;

ASSERT_DICT_LOCKED(self);

/* Allocate the result tuple before checking the size. Believe it
* or not, this allocation could trigger a garbage collection which
* could empty the dict, so if we checked the size first and that
Expand Down Expand Up @@ -4799,11 +4806,12 @@ _PyDict_SizeOf_LockHeld(PyDictObject *mp)
}

void
_PyDict_ClearKeysVersionLockHeld(PyObject *mp)
_PyDict_ClearKeysVersionLockHeld(PyObject *op)
{
ASSERT_DICT_LOCKED(mp);
PyDictObject *mp = _PyAnyDict_CAST(op);
assert(can_modify_dict(mp));

FT_ATOMIC_STORE_UINT32_RELAXED(((PyDictObject *)mp)->ma_keys->dk_version, 0);
FT_ATOMIC_STORE_UINT32_RELAXED(mp->ma_keys->dk_version, 0);
}

Py_ssize_t
Expand Down
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