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gh-120198: Stop the world when setting __class__ on free-threaded build #120672

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merged 8 commits into from
Jul 10, 2024
Merged

gh-120198: Stop the world when setting __class__ on free-threaded build #120672

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2e5667e
Stop the world when setting __class__
Fidget-Spinner Jun 18, 2024
b482f87
Address reviews
Fidget-Spinner Jun 18, 2024
d2a7095
fix non-free-threaded builds
Fidget-Spinner Jun 18, 2024
8a562ce
Address review
Fidget-Spinner Jun 19, 2024
a88d238
Merge remote-tracking branch 'upstream/main' into class_stoptheworld
Fidget-Spinner Jun 19, 2024
8a25bfb
Address Sam's reviews
Fidget-Spinner Jun 21, 2024
13486cb
fix name
Fidget-Spinner Jun 21, 2024
a409ab2
Address reviews
Fidget-Spinner Jul 10, 2024
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8 changes: 0 additions & 8 deletions Include/object.h
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Original file line number Diff line number Diff line change
Expand Up @@ -246,11 +246,7 @@ _Py_IsOwnedByCurrentThread(PyObject *ob)

// bpo-39573: The Py_SET_TYPE() function must be used to set an object type.
static inline PyTypeObject* Py_TYPE(PyObject *ob) {
#ifdef Py_GIL_DISABLED
return (PyTypeObject *)_Py_atomic_load_ptr_relaxed(&ob->ob_type);
#else
return ob->ob_type;
#endif
}
#if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 < 0x030b0000
# define Py_TYPE(ob) Py_TYPE(_PyObject_CAST(ob))
Expand Down Expand Up @@ -278,11 +274,7 @@ static inline int Py_IS_TYPE(PyObject *ob, PyTypeObject *type) {


static inline void Py_SET_TYPE(PyObject *ob, PyTypeObject *type) {
#ifdef Py_GIL_DISABLED
_Py_atomic_store_ptr(&ob->ob_type, type);
#else
ob->ob_type = type;
#endif
}
#if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 < 0x030b0000
# define Py_SET_TYPE(ob, type) Py_SET_TYPE(_PyObject_CAST(ob), type)
Expand Down
7 changes: 6 additions & 1 deletion Objects/dictobject.c
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Original file line number Diff line number Diff line change
Expand Up @@ -158,6 +158,10 @@ ASSERT_DICT_LOCKED(PyObject *op)
if (!_PyInterpreterState_GET()->stoptheworld.world_stopped) { \
ASSERT_DICT_LOCKED(op); \
}
#define ASSERT_WORLD_STOPPED_OR_OBJ_LOCKED(op) \
if (!_PyInterpreterState_GET()->stoptheworld.world_stopped) { \
_Py_CRITICAL_SECTION_ASSERT_OBJECT_LOCKED(op); \
}

#define IS_DICT_SHARED(mp) _PyObject_GC_IS_SHARED(mp)
#define SET_DICT_SHARED(mp) _PyObject_GC_SET_SHARED(mp)
Expand Down Expand Up @@ -227,6 +231,7 @@ static inline void split_keys_entry_added(PyDictKeysObject *keys)

#define ASSERT_DICT_LOCKED(op)
#define ASSERT_WORLD_STOPPED_OR_DICT_LOCKED(op)
#define ASSERT_WORLD_STOPPED_OR_OBJ_LOCKED(op)
#define LOCK_KEYS(keys)
#define UNLOCK_KEYS(keys)
#define ASSERT_KEYS_LOCKED(keys)
Expand Down Expand Up @@ -7170,7 +7175,7 @@ PyObject_ClearManagedDict(PyObject *obj)
int
_PyDict_DetachFromObject(PyDictObject *mp, PyObject *obj)
{
_Py_CRITICAL_SECTION_ASSERT_OBJECT_LOCKED(obj);
ASSERT_WORLD_STOPPED_OR_OBJ_LOCKED(obj);
assert(_PyObject_ManagedDictPointer(obj)->dict == mp);
assert(_PyObject_InlineValuesConsistencyCheck(obj));

Expand Down
39 changes: 23 additions & 16 deletions Objects/typeobject.c
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Expand Up @@ -6599,6 +6599,12 @@ object_set_class(PyObject *self, PyObject *value, void *closure)
}

PyTypeObject *oldto = Py_TYPE(self);
#ifdef Py_GIL_DISABLED
PyInterpreterState *interp = _PyInterpreterState_GET();
// The real Py_TYPE(self) (`oldto`) may have changed from
// underneath us in another thread, so we re-fetch it here.
_PyEval_StopTheWorld(interp);
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#endif

/* In versions of CPython prior to 3.5, the code in
compatible_for_assignment was not set up to correctly check for memory
Expand Down Expand Up @@ -6656,7 +6662,7 @@ object_set_class(PyObject *self, PyObject *value, void *closure)
PyErr_Format(PyExc_TypeError,
"__class__ assignment only supported for mutable types "
"or ModuleType subclasses");
return -1;
goto err;
}

if (compatible_for_assignment(oldto, newto, "__class__")) {
Expand All @@ -6665,47 +6671,48 @@ object_set_class(PyObject *self, PyObject *value, void *closure)
if (oldto->tp_flags & Py_TPFLAGS_INLINE_VALUES) {
PyDictObject *dict = _PyObject_MaterializeManagedDict(self);
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if (dict == NULL) {
return -1;
goto err;
}

bool error = false;

Py_BEGIN_CRITICAL_SECTION2(self, dict);

// If we raced after materialization and replaced the dict
// then the materialized dict should no longer have the
// inline values in which case detach is a nop.
// Note: we don't need to lock here because the world should be stopped.
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assert(_PyObject_GetManagedDict(self) == dict ||
dict->ma_values != _PyObject_InlineValues(self));
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if (_PyDict_DetachFromObject(dict, self) < 0) {
error = true;
goto err;
}

Py_END_CRITICAL_SECTION2();
if (error) {
return -1;
}
}
if (newto->tp_flags & Py_TPFLAGS_HEAPTYPE) {
Py_INCREF(newto);
}
Py_BEGIN_CRITICAL_SECTION(self);
// The real Py_TYPE(self) (`oldto`) may have changed from
// underneath us in another thread, so we re-fetch it here.

oldto = Py_TYPE(self);
Py_SET_TYPE(self, newto);
Py_END_CRITICAL_SECTION();

if (oldto->tp_flags & Py_TPFLAGS_HEAPTYPE) {
Py_DECREF(oldto);
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}

RARE_EVENT_INC(set_class);

#ifdef Py_GIL_DISABLED
_PyEval_StartTheWorld(interp);
#endif
return 0;
}
else {
return -1;
goto err;
}
err:
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To have a more regular try: ... finally: _PyEval_StartTheWorld() pattern, you can add an int res = -1; variable, replace goto err with goto done, and set res to 0 on success (3 lines above).

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I think @vstinner's suggestion is fine. Or you can refactor the parts that should be in a stop-the-world call into it's own function, like we often do for locks.

Another advantage of moving the body to a separate function is that it makes it more clear what data crosses the stop-the-world boundary -- some data loaded before the stop-the-world call may not be valid after it.

#ifdef Py_GIL_DISABLED
_PyEval_StartTheWorld(interp);
#endif
return -1;
}

static PyGetSetDef object_getsets[] = {
Expand Down
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