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gh-104252: Immortalize Py_EMPTY_KEYS #104253

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Merged
merged 10 commits into from
May 10, 2023
Merged

gh-104252: Immortalize Py_EMPTY_KEYS #104253

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5bc2469
Factor out _dict_state_INIT.
ericsnowcurrently May 6, 2023
e472d94
Immortalize Py_EMPTY_KEYS.
ericsnowcurrently May 6, 2023
87351e0
Handle other uses of dk_refcnt.
ericsnowcurrently May 8, 2023
f5da088
Add a note.
ericsnowcurrently May 8, 2023
db8612f
Drop an old line.
ericsnowcurrently May 8, 2023
58585a9
Drop an unnecessary condition.
ericsnowcurrently May 8, 2023
6b5c952
Drop an unnecessary assert.
ericsnowcurrently May 9, 2023
bdbce5f
Do not bother inc/dec-refing Py_EMPTY_KEYS.
ericsnowcurrently May 9, 2023
aab493a
Do not update Py_Reftotal for Py_EMPTY_KEYS.
ericsnowcurrently May 9, 2023
5aabfd7
Clarify the comment about dictkeys_incref() and dictkeys_decref().
ericsnowcurrently May 9, 2023
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7 changes: 7 additions & 0 deletions Include/internal/pycore_dict_state.h
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Original file line number Diff line number Diff line change
Expand Up @@ -27,6 +27,8 @@ struct _Py_dict_state {
uint64_t global_version;
uint32_t next_keys_version;

// PyDictKeysObject empty_keys_struct;

#if PyDict_MAXFREELIST > 0
/* Dictionary reuse scheme to save calls to malloc and free */
PyDictObject *free_list[PyDict_MAXFREELIST];
Expand All @@ -38,6 +40,11 @@ struct _Py_dict_state {
PyDict_WatchCallback watchers[DICT_MAX_WATCHERS];
};

#define _dict_state_INIT \
{ \
.next_keys_version = 2, \
}


#ifdef __cplusplus
}
Expand Down
4 changes: 1 addition & 3 deletions Include/internal/pycore_runtime_init.h
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Expand Up @@ -107,9 +107,7 @@ extern PyTypeObject _PyExc_MemoryError;
}, \
}, \
.dtoa = _dtoa_state_INIT(&(INTERP)), \
.dict_state = { \
.next_keys_version = 2, \
}, \
.dict_state = _dict_state_INIT, \
.func_state = { \
.next_version = 1, \
}, \
Expand Down
27 changes: 18 additions & 9 deletions Objects/dictobject.c
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Expand Up @@ -300,9 +300,18 @@ _PyDict_DebugMallocStats(FILE *out)

static void free_keys_object(PyInterpreterState *interp, PyDictKeysObject *keys);

/* We might consider modifying PyDictKeysObject so we could use
Py_INCREF() instead of dictkeys_incref() (and likewise with
Py_DECREF() and dictkeys_decref()). However, there doesn't
seem to be enough benefit (performance or otherwise) to justify
the change. */

static inline void
dictkeys_incref(PyDictKeysObject *dk)
{
if (dk->dk_refcnt == _Py_IMMORTAL_REFCNT) {
return;
}
#ifdef Py_REF_DEBUG
_Py_IncRefTotal(_PyInterpreterState_GET());
#endif
Expand All @@ -312,6 +321,9 @@ dictkeys_incref(PyDictKeysObject *dk)
static inline void
dictkeys_decref(PyInterpreterState *interp, PyDictKeysObject *dk)
{
if (dk->dk_refcnt == _Py_IMMORTAL_REFCNT) {
return;
}
assert(dk->dk_refcnt > 0);
#ifdef Py_REF_DEBUG
_Py_DecRefTotal(_PyInterpreterState_GET());
Expand Down Expand Up @@ -447,7 +459,7 @@ estimate_log2_keysize(Py_ssize_t n)
* (which cannot fail and thus can do no allocation).
*/
static PyDictKeysObject empty_keys_struct = {
1, /* dk_refcnt */
_Py_IMMORTAL_REFCNT, /* dk_refcnt */
0, /* dk_log2_size */
0, /* dk_log2_index_bytes */
DICT_KEYS_UNICODE, /* dk_kind */
Expand Down Expand Up @@ -779,6 +791,7 @@ clone_combined_dict_keys(PyDictObject *orig)
assert(PyDict_Check(orig));
assert(Py_TYPE(orig)->tp_iter == (getiterfunc)dict_iter);
assert(orig->ma_values == NULL);
assert(orig->ma_keys != Py_EMPTY_KEYS);
assert(orig->ma_keys->dk_refcnt == 1);

size_t keys_size = _PyDict_KeysSize(orig->ma_keys);
Expand Down Expand Up @@ -1532,11 +1545,7 @@ dictresize(PyInterpreterState *interp, PyDictObject *mp,
#ifdef Py_REF_DEBUG
_Py_DecRefTotal(_PyInterpreterState_GET());
#endif
if (oldkeys == Py_EMPTY_KEYS) {
oldkeys->dk_refcnt--;
assert(oldkeys->dk_refcnt > 0);
}
else {
if (oldkeys != Py_EMPTY_KEYS) {
assert(oldkeys->dk_kind != DICT_KEYS_SPLIT);
assert(oldkeys->dk_refcnt == 1);
#if PyDict_MAXFREELIST > 0
Expand Down Expand Up @@ -2080,8 +2089,8 @@ PyDict_Clear(PyObject *op)
dictkeys_decref(interp, oldkeys);
}
else {
assert(oldkeys->dk_refcnt == 1);
dictkeys_decref(interp, oldkeys);
assert(oldkeys->dk_refcnt == 1 || oldkeys == Py_EMPTY_KEYS);
dictkeys_decref(interp, oldkeys);
}
ASSERT_CONSISTENT(mp);
}
Expand Down Expand Up @@ -3565,7 +3574,7 @@ _PyDict_SizeOf(PyDictObject *mp)
}
/* If the dictionary is split, the keys portion is accounted-for
in the type object. */
if (mp->ma_keys->dk_refcnt == 1) {
if (mp->ma_keys->dk_refcnt == 1 || mp->ma_keys == Py_EMPTY_KEYS) {
res += _PyDict_KeysSize(mp->ma_keys);
}
assert(res <= (size_t)PY_SSIZE_T_MAX);
Expand Down