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gh-112075: Make _PyDict_LoadGlobal thread safe by DinoV · Pull Request #117529 · python/cpython · GitHub

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gh-112075: Make _PyDict_LoadGlobal thread safe #117529

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Merged
DinoV merged 2 commits into from
Apr 4, 2024
Conversation 4 Commits 2 Checks 0 Files changed
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gh-112075: Make _PyDict_LoadGlobal thread safe #117529

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548a7c2
Make _PyDict_LoadGlobal threadsafe
DinoV Apr 3, 2024
3dd1182
Add version of _Py_dict_lookup_threadsafe w/ the GIL that does incref
DinoV Apr 4, 2024
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1 change: 1 addition & 0 deletions Include/internal/pycore_dict.h
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Original file line number Diff line number Diff line change
Expand Up @@ -97,6 +97,7 @@ extern void _PyDictKeys_DecRef(PyDictKeysObject *keys);
* -1 when no entry found, -3 when compare raises error.
*/
extern Py_ssize_t _Py_dict_lookup(PyDictObject *mp, PyObject *key, Py_hash_t hash, PyObject **value_addr);
extern Py_ssize_t _Py_dict_lookup_threadsafe(PyDictObject *mp, PyObject *key, Py_hash_t hash, PyObject **value_addr);

extern Py_ssize_t _PyDict_LookupIndex(PyDictObject *, PyObject *);
extern Py_ssize_t _PyDictKeys_StringLookup(PyDictKeysObject* dictkeys, PyObject *key);
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42 changes: 17 additions & 25 deletions Objects/dictobject.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1065,7 +1065,6 @@ compare_unicode_generic(PyDictObject *mp, PyDictKeysObject *dk,
assert(ep->me_key != NULL);
assert(PyUnicode_CheckExact(ep->me_key));
assert(!PyUnicode_CheckExact(key));
// TODO: Thread safety

if (unicode_get_hash(ep->me_key) == hash) {
PyObject *startkey = ep->me_key;
Expand Down Expand Up @@ -1192,7 +1191,8 @@ _Py_dict_lookup(PyDictObject *mp, PyObject *key, Py_hash_t hash, PyObject **valu
PyDictKeysObject *dk;
DictKeysKind kind;
Py_ssize_t ix;
// TODO: Thread safety

_Py_CRITICAL_SECTION_ASSERT_OBJECT_LOCKED(mp);
start:
dk = mp->ma_keys;
kind = dk->dk_kind;
Expand Down Expand Up @@ -1390,7 +1390,7 @@ dictkeys_generic_lookup_threadsafe(PyDictObject *mp, PyDictKeysObject* dk, PyObj
return do_lookup(mp, dk, key, hash, compare_generic_threadsafe);
}

static Py_ssize_t
Py_ssize_t
_Py_dict_lookup_threadsafe(PyDictObject *mp, PyObject *key, Py_hash_t hash, PyObject **value_addr)
{
PyDictKeysObject *dk;
Expand Down Expand Up @@ -1488,6 +1488,16 @@ _Py_dict_lookup_threadsafe(PyDictObject *mp, PyObject *key, Py_hash_t hash, PyOb
return ix;
}

#else // Py_GIL_DISABLED

Py_ssize_t
_Py_dict_lookup_threadsafe(PyDictObject *mp, PyObject *key, Py_hash_t hash, PyObject **value_addr)
{
Py_ssize_t ix = _Py_dict_lookup(mp, key, hash, value_addr);
Py_XNewRef(*value_addr);
return ix;
}

#endif

int
Expand Down Expand Up @@ -2343,11 +2353,12 @@ _PyDict_GetItemStringWithError(PyObject *v, const char *key)
* Raise an exception and return NULL if an error occurred (ex: computing the
* key hash failed, key comparison failed, ...). Return NULL if the key doesn't
* exist. Return the value if the key exists.
*
* Returns a new reference.

colesbury Apr 4, 2024

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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

I think we will want it to return a possibly deferred reference soon, but this is good for now.
*/
PyObject *
_PyDict_LoadGlobal(PyDictObject *globals, PyDictObject *builtins, PyObject *key)
{
// TODO: Thread safety
Py_ssize_t ix;
Py_hash_t hash;
PyObject *value;
Expand All @@ -2359,14 +2370,14 @@ _PyDict_LoadGlobal(PyDictObject *globals, PyDictObject *builtins, PyObject *key)
}

/* namespace 1: globals */
ix = _Py_dict_lookup(globals, key, hash, &value);
ix = _Py_dict_lookup_threadsafe(globals, key, hash, &value);

colesbury Apr 4, 2024

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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

I think this pattern might be simpler if we define _Py_dict_lookup_threadsafe in the default build as _Py_dict_lookup_threadsafe + Py_XNewRef().

We could use it in dict_subscript and dict_get_impl as well.
if (ix == DKIX_ERROR)
return NULL;
if (ix != DKIX_EMPTY && value != NULL)
return value;

/* namespace 2: builtins */
ix = _Py_dict_lookup(builtins, key, hash, &value);
ix = _Py_dict_lookup_threadsafe(builtins, key, hash, &value);
assert(ix >= 0 || value == NULL);
return value;
}
Expand Down Expand Up @@ -3214,11 +3225,7 @@ dict_subscript(PyObject *self, PyObject *key)
if (hash == -1)
return NULL;
}
#ifdef Py_GIL_DISABLED
ix = _Py_dict_lookup_threadsafe(mp, key, hash, &value);
#else
ix = _Py_dict_lookup(mp, key, hash, &value);
#endif
if (ix == DKIX_ERROR)
return NULL;
if (ix == DKIX_EMPTY || value == NULL) {
Expand All @@ -3238,11 +3245,7 @@ dict_subscript(PyObject *self, PyObject *key)
_PyErr_SetKeyError(key);
return NULL;
}
#ifdef Py_GIL_DISABLED
return value;
#else
return Py_NewRef(value);
#endif
}

static int
Expand Down Expand Up @@ -4109,24 +4112,13 @@ dict_get_impl(PyDictObject *self, PyObject *key, PyObject *default_value)
if (hash == -1)
return NULL;
}
#ifdef Py_GIL_DISABLED
ix = _Py_dict_lookup_threadsafe(self, key, hash, &val);
#else
ix = _Py_dict_lookup(self, key, hash, &val);
#endif
if (ix == DKIX_ERROR)
return NULL;
#ifdef Py_GIL_DISABLED
if (ix == DKIX_EMPTY || val == NULL) {
val = Py_NewRef(default_value);
}
return val;
#else
if (ix == DKIX_EMPTY || val == NULL) {
val = default_value;
}
return Py_NewRef(val);
#endif
}

static int
Expand Down
6 changes: 5 additions & 1 deletion Objects/odictobject.c
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Expand Up @@ -535,8 +535,12 @@ _odict_get_index_raw(PyODictObject *od, PyObject *key, Py_hash_t hash)
PyObject *value = NULL;
PyDictKeysObject *keys = ((PyDictObject *)od)->ma_keys;
Py_ssize_t ix;

#ifdef Py_GIL_DISABLED
ix = _Py_dict_lookup_threadsafe((PyDictObject *)od, key, hash, &value);
Py_XDECREF(value);
#else
ix = _Py_dict_lookup((PyDictObject *)od, key, hash, &value);
#endif
if (ix == DKIX_EMPTY) {
return keys->dk_nentries; /* index of new entry */
}
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1 change: 0 additions & 1 deletion Python/bytecodes.c
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Expand Up @@ -1426,7 +1426,6 @@ dummy_func(
}
ERROR_IF(true, error);
}
Py_INCREF(res);
}
else {
/* Slow-path if globals or builtins is not a dict */
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1 change: 0 additions & 1 deletion Python/executor_cases.c.h
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1 change: 0 additions & 1 deletion Python/generated_cases.c.h
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