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GH-137759:Limit _PyObject_HashFast to dicts keys, rename it, and mark it as Py_ALWAYS_INLINE #137828

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GH-137759:Limit _PyObject_HashFast to dicts keys, rename it, and mark it as Py_ALWAYS_INLINE #137828

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1521fb1
GH-137759: Limit _PyObject_HashFast to dict keys
JasonMendoza2008 May 31, 2026
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Apply suggestion from @serhiy-storchaka
serhiy-storchaka Jun 6, 2026
3a42bfc
Merge branch 'main' into fix-issue-137759
serhiy-storchaka Jun 6, 2026
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11 changes: 8 additions & 3 deletions Include/internal/pycore_object.h
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Expand Up @@ -836,9 +836,14 @@ _PyObject_IS_GC(PyObject *obj)
&& (type->tp_is_gc == NULL || type->tp_is_gc(obj)));
}

// Fast inlined version of PyObject_Hash()
static inline Py_hash_t
_PyObject_HashFast(PyObject *op)
// Fast inlined version of PyObject_Hash(). Dictionaries are very
// likely to include string keys (class and instance attributes,
// json, ...) so we include a fast path for strings.
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serhiy-storchaka marked this conversation as resolved.
// This function should not be used in a collection if str is not
// very likely, since it is slower than PyObject_Hash() on types
// other than str.

@vstinner vstinner Jun 8, 2026

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Please add a sentence to explain explicitly that the function is used for dict since dict keys are likely strings, but it's not used for set since set items are less likely to be strings.

@vstinner vstinner Jun 8, 2026

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And add a reference to the issue: gh-137759: (...).

static inline Py_ALWAYS_INLINE Py_hash_t
_PyObject_HashDictKey(PyObject *op)
{
if (PyUnicode_CheckExact(op)) {
Py_hash_t hash = PyUnstable_Unicode_GET_CACHED_HASH(op);
Expand Down
2 changes: 1 addition & 1 deletion Modules/_collectionsmodule.c
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Expand Up @@ -2590,7 +2590,7 @@ _collections__count_elements_impl(PyObject *module, PyObject *mapping,
if (key == NULL)
break;

hash = _PyObject_HashFast(key);
hash = _PyObject_HashDictKey(key);
if (hash == -1) {
goto done;
}
Expand Down
30 changes: 15 additions & 15 deletions Objects/dictobject.c
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Expand Up @@ -2357,7 +2357,7 @@ dict_getitem(PyObject *op, PyObject *key, const char *warnmsg)
}
PyDictObject *mp = (PyDictObject *)op;

Py_hash_t hash = _PyObject_HashFast(key);
Py_hash_t hash = _PyObject_HashDictKey(key);
if (hash == -1) {
PyErr_FormatUnraisable(warnmsg);
return NULL;
Expand Down Expand Up @@ -2429,7 +2429,7 @@ _PyDict_LookupIndexAndValue(PyDictObject *mp, PyObject *key, PyObject **value)
assert(PyDict_CheckExact((PyObject*)mp));
assert(PyUnicode_CheckExact(key));

Py_hash_t hash = _PyObject_HashFast(key);
Py_hash_t hash = _PyObject_HashDictKey(key);
if (hash == -1) {
dict_unhashable_type((PyObject*)mp, key);
return -1;
Expand Down Expand Up @@ -2533,7 +2533,7 @@ PyDict_GetItemRef(PyObject *op, PyObject *key, PyObject **result)
return -1;
}

Py_hash_t hash = _PyObject_HashFast(key);
Py_hash_t hash = _PyObject_HashDictKey(key);
if (hash == -1) {
dict_unhashable_type(op, key);
*result = NULL;
Expand All @@ -2549,7 +2549,7 @@ _PyDict_GetItemRef_Unicode_LockHeld(PyDictObject *op, PyObject *key, PyObject **
ASSERT_DICT_LOCKED(op);
assert(PyUnicode_CheckExact(key));

Py_hash_t hash = _PyObject_HashFast(key);
Py_hash_t hash = _PyObject_HashDictKey(key);
if (hash == -1) {
dict_unhashable_type((PyObject*)op, key);
*result = NULL;
Expand Down Expand Up @@ -2587,7 +2587,7 @@ PyDict_GetItemWithError(PyObject *op, PyObject *key)
PyErr_BadInternalCall();
return NULL;
}
hash = _PyObject_HashFast(key);
hash = _PyObject_HashDictKey(key);
if (hash == -1) {
dict_unhashable_type(op, key);
return NULL;
Expand Down Expand Up @@ -2646,7 +2646,7 @@ _PyDict_LoadGlobal(PyDictObject *globals, PyDictObject *builtins, PyObject *key)
Py_hash_t hash;
PyObject *value;

hash = _PyObject_HashFast(key);
hash = _PyObject_HashDictKey(key);
if (hash == -1) {
return NULL;
}
Expand All @@ -2670,7 +2670,7 @@ _PyDict_LoadGlobalStackRef(PyDictObject *globals, PyDictObject *builtins, PyObje
Py_ssize_t ix;
Py_hash_t hash;

hash = _PyObject_HashFast(key);
hash = _PyObject_HashDictKey(key);
if (hash == -1) {
*res = PyStackRef_NULL;
return;
Expand Down Expand Up @@ -2747,7 +2747,7 @@ setitem_take2_lock_held_known_hash(PyDictObject *mp, PyObject *key, PyObject *va
static int
setitem_take2_lock_held(PyDictObject *mp, PyObject *key, PyObject *value)
{
Py_hash_t hash = _PyObject_HashFast(key);
Py_hash_t hash = _PyObject_HashDictKey(key);
if (hash == -1) {
dict_unhashable_type((PyObject*)mp, key);
Py_DECREF(key);
Expand Down Expand Up @@ -2925,7 +2925,7 @@ int
PyDict_DelItem(PyObject *op, PyObject *key)
{
assert(key);
Py_hash_t hash = _PyObject_HashFast(key);
Py_hash_t hash = _PyObject_HashDictKey(key);
if (hash == -1) {
dict_unhashable_type(op, key);
return -1;
Expand Down Expand Up @@ -3269,7 +3269,7 @@ pop_lock_held(PyObject *op, PyObject *key, PyObject **result)
return 0;
}

Py_hash_t hash = _PyObject_HashFast(key);
Py_hash_t hash = _PyObject_HashDictKey(key);
if (hash == -1) {
dict_unhashable_type(op, key);
if (result) {
Expand Down Expand Up @@ -3707,7 +3707,7 @@ _PyDict_SubscriptKnownHash(PyObject *self, PyObject *key, Py_hash_t hash)
PyObject *
_PyDict_Subscript(PyObject *self, PyObject *key)
{
Py_hash_t hash = _PyObject_HashFast(key);
Py_hash_t hash = _PyObject_HashDictKey(key);
if (hash == -1) {
dict_unhashable_type(self, key);
return NULL;
Expand Down Expand Up @@ -4659,7 +4659,7 @@ dict_get_impl(PyDictObject *self, PyObject *key, PyObject *default_value)
Py_hash_t hash;
Py_ssize_t ix;

hash = _PyObject_HashFast(key);
hash = _PyObject_HashDictKey(key);
if (hash == -1) {
dict_unhashable_type((PyObject*)self, key);
return NULL;
Expand Down Expand Up @@ -4696,7 +4696,7 @@ dict_setdefault_ref_lock_held(PyObject *d, PyObject *key, PyObject *default_valu
Py_hash_t hash;
Py_ssize_t ix;

hash = _PyObject_HashFast(key);
hash = _PyObject_HashDictKey(key);
if (hash == -1) {
dict_unhashable_type(d, key);
if (result) {
Expand Down Expand Up @@ -5138,7 +5138,7 @@ static PyMethodDef mapp_methods[] = {
static int
dict_contains(PyObject *op, PyObject *key)
{
Py_hash_t hash = _PyObject_HashFast(key);
Py_hash_t hash = _PyObject_HashDictKey(key);
if (hash == -1) {
dict_unhashable_type(op, key);
return -1;
Expand Down Expand Up @@ -7244,7 +7244,7 @@ _PyDict_SetItem_LockHeld(PyDictObject *dict, PyObject *name, PyObject *value)
}

if (value == NULL) {
Py_hash_t hash = _PyObject_HashFast(name);
Py_hash_t hash = _PyObject_HashDictKey(name);
if (hash == -1) {
dict_unhashable_type((PyObject*)dict, name);
return -1;
Expand Down
14 changes: 7 additions & 7 deletions Objects/setobject.c
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Expand Up @@ -361,7 +361,7 @@ set_unhashable_type(PyObject *key)
int
_PySet_AddTakeRef(PySetObject *so, PyObject *key)
{
Py_hash_t hash = _PyObject_HashFast(key);
Py_hash_t hash = PyObject_Hash(key);
if (hash == -1) {
set_unhashable_type(key);
Py_DECREF(key);
Expand Down Expand Up @@ -600,7 +600,7 @@ set_discard_entry(PySetObject *so, PyObject *key, Py_hash_t hash)
static int
set_add_key(PySetObject *so, PyObject *key)
{
Py_hash_t hash = _PyObject_HashFast(key);
Py_hash_t hash = PyObject_Hash(key);
if (hash == -1) {
set_unhashable_type(key);
return -1;
Expand All @@ -611,7 +611,7 @@ set_add_key(PySetObject *so, PyObject *key)
static int
set_contains_key(PySetObject *so, PyObject *key)
{
Py_hash_t hash = _PyObject_HashFast(key);
Py_hash_t hash = PyObject_Hash(key);
if (hash == -1) {
set_unhashable_type(key);
return -1;
Expand All @@ -622,7 +622,7 @@ set_contains_key(PySetObject *so, PyObject *key)
static int
set_discard_key(PySetObject *so, PyObject *key)
{
Py_hash_t hash = _PyObject_HashFast(key);
Py_hash_t hash = PyObject_Hash(key);
if (hash == -1) {
set_unhashable_type(key);
return -1;
Expand Down Expand Up @@ -2514,7 +2514,7 @@ _PySet_Contains(PySetObject *so, PyObject *key)
{
assert(so);

Py_hash_t hash = _PyObject_HashFast(key);
Py_hash_t hash = PyObject_Hash(key);
if (hash == -1) {
if (!PySet_Check(key) || !PyErr_ExceptionMatches(PyExc_TypeError)) {
set_unhashable_type(key);
Expand Down Expand Up @@ -2574,7 +2574,7 @@ static PyObject *
frozenset___contains___impl(PySetObject *so, PyObject *key)
/*[clinic end generated code: output=2301ed91bc3a6dd5 input=2f04922a98d8bab7]*/
{
Py_hash_t hash = _PyObject_HashFast(key);
Py_hash_t hash = PyObject_Hash(key);
if (hash == -1) {
if (!PySet_Check(key) || !PyErr_ExceptionMatches(PyExc_TypeError)) {
set_unhashable_type(key);
Expand Down Expand Up @@ -3039,7 +3039,7 @@ PySet_Contains(PyObject *anyset, PyObject *key)
}

PySetObject *so = (PySetObject *)anyset;
Py_hash_t hash = _PyObject_HashFast(key);
Py_hash_t hash = PyObject_Hash(key);
if (hash == -1) {
set_unhashable_type(key);
return -1;
Expand Down
4 changes: 2 additions & 2 deletions Objects/typeobject.c
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Expand Up @@ -3788,7 +3788,7 @@ solid_base(PyTypeObject *type)
// or when __bases__ is re-assigned. Since the slots are read without atomic
// operations and without locking, we can only safely update them while the
// world is stopped. However, with the world stopped, we are very limited on
// which APIs can be safely used. For example, calling _PyObject_HashFast()
// which APIs can be safely used. For example, calling _PyObject_HashDictKey()
// or _PyDict_GetItemRef_KnownHash() are not safe and can potentially cause
// deadlocks. Hashing can be re-entrant and _PyDict_GetItemRef_KnownHash can
// acquire a lock if the dictionary is not owned by the current thread, to
Expand Down Expand Up @@ -6129,7 +6129,7 @@ PyObject_GetItemData(PyObject *obj)
static int
find_name_in_mro(PyTypeObject *type, PyObject *name, _PyStackRef *out)
{
Py_hash_t hash = _PyObject_HashFast(name);
Py_hash_t hash = _PyObject_HashDictKey(name);
if (hash == -1) {
PyErr_Clear();
return -1;
Expand Down
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