May 28, 2025 · Apr 29, 2025 · Apr 29, 2025 · Apr 29, 2025 · Apr 30, 2025 · Apr 30, 2025
diff --git a/Include/internal/pycore_interp_structs.h b/Include/internal/pycore_interp_structs.h

    /* object.__reduce__ */
    PyObject *objreduce;
 #ifndef Py_GIL_DISABLED
    /* resolve_slotdups() */
    PyObject *type_slots_pname;
    pytype_slotdef *type_slots_ptrs[MAX_EQUIV];
 #endif

    /* TypeVar and related types */
    PyTypeObject *generic_type;
diff --git a/Include/internal/pycore_object.h b/Include/internal/pycore_object.h
 // Fast inlined version of PyType_HasFeature()
 static inline int
 _PyType_HasFeature(PyTypeObject *type, unsigned long feature) {
    return ((FT_ATOMIC_LOAD_ULONG_RELAXED(type->tp_flags) & feature) != 0);
    return ((type->tp_flags) & feature) != 0;
 }

 extern void _PyType_InitCache(PyInterpreterState *interp);
diff --git a/Include/internal/pycore_typeobject.h b/Include/internal/pycore_typeobject.h
 extern void _PyType_SetFlagsRecursive(PyTypeObject *self, unsigned long mask,
                                      unsigned long flags);

 extern unsigned int _PyType_GetVersionForCurrentState(PyTypeObject *tp);
 PyAPI_FUNC(void) _PyType_SetVersion(PyTypeObject *tp, unsigned int version);
 PyTypeObject *_PyType_LookupByVersion(unsigned int version);

diff --git a/Include/object.h b/Include/object.h
 #define Py_TPFLAGS_HAVE_FINALIZE (1UL << 0)
 #define Py_TPFLAGS_HAVE_VERSION_TAG   (1UL << 18)

 // Flag values for ob_flags (16 bits available, if SIZEOF_VOID_P > 4).
 #define _Py_IMMORTAL_FLAGS (1 << 0)
 #define _Py_STATICALLY_ALLOCATED_FLAG (1 << 2)
 #if defined(Py_GIL_DISABLED) && defined(Py_DEBUG)
 #define _Py_TYPE_REVEALED_FLAG (1 << 3)
 #endif

 #define Py_CONSTANT_NONE 0
 #define Py_CONSTANT_FALSE 1
    // PyTypeObject is opaque in the limited C API
    flags = PyType_GetFlags(type);
 #else
 #   ifdef Py_GIL_DISABLED
        flags = _Py_atomic_load_ulong_relaxed(&type->tp_flags);
 #   else
        flags = type->tp_flags;
 #   endif
    flags = type->tp_flags;
 #endif
    return ((flags & feature) != 0);
 }
diff --git a/Include/refcount.h b/Include/refcount.h
 cleanup during runtime finalization.
 */

 #define _Py_STATICALLY_ALLOCATED_FLAG 4
 #define _Py_IMMORTAL_FLAGS 1

 #if SIZEOF_VOID_P > 4
 /*
 In 64+ bit systems, any object whose 32 bit reference count is >= 2**31
diff --git a/Lib/test/test_descr.py b/Lib/test/test_descr.py
        else:
            self.fail("shouldn't be able to create inheritance cycles")

    def test_assign_bases_many_subclasses(self):
        class A:
            x = 'hello'
            def __call__(self):
                return 123
            def __getitem__(self, index):
                return None

        class X:
            x = 'bye'

        class B(A):
            pass

        subclasses = []
        for i in range(1000):
            sc = type(f'Sub{i}', (B,), {})
            subclasses.append(sc)

        self.assertEqual(subclasses[0]()(), 123)
        self.assertEqual(subclasses[0]().x, 'hello')
        B.__bases__ = (X,)
        with self.assertRaises(TypeError):
            subclasses[0]()()
        self.assertEqual(subclasses[0]().x, 'bye')

    def test_builtin_bases(self):
        # Make sure all the builtin types can have their base queried without
        # segfaulting. See issue #5787.
diff --git a/Lib/test/test_opcache.py b/Lib/test/test_opcache.py
    # Careful with these. Bigger numbers have a higher chance of catching bugs,
    # but you can also burn through a *ton* of type/dict/function versions:
    ITEMS = 1000
    SMALL_ITEMS = 100
    LOOPS = 4
    WRITERS = 2

                __getitem__ = lambda self, item: None

            items = []
            for _ in range(self.ITEMS):
            for _ in range(self.SMALL_ITEMS):
                item = C()
                items.append(item)
            return items
                __getattribute__ = lambda self, name: None

            items = []
            for _ in range(self.ITEMS):
            for _ in range(self.SMALL_ITEMS):
                item = C()
                items.append(item)
            return items
diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2025-03-14-13-08-20.gh-issue-127266._tyfBp.rst b/Misc/NEWS.d/next/Core_and_Builtins/2025-03-14-13-08-20.gh-issue-127266._tyfBp.rst
 In the free-threaded build, avoid data races caused by updating type slots
 or type flags after the type was initially created.  For those (typically
 rare) cases, use the stop-the-world mechanism.  Remove the use of atomics
 when reading or writing type flags.  The use of atomics is not sufficient to
 avoid races (since flags are sometimes read without a lock and without
 atomics) and are no longer required.
Original file line number	Diff line number	Diff line change
Expand Up		@@ -667,8 +667,11 @@ struct _Py_interp_cached_objects {

		/* object.__reduce__ */
		PyObject *objreduce;
		#ifndef Py_GIL_DISABLED
		/* resolve_slotdups() */
		PyObject *type_slots_pname;
		pytype_slotdef *type_slots_ptrs[MAX_EQUIV];
		#endif

		/* TypeVar and related types */
		PyTypeObject *generic_type;
Expand Down
Original file line number	Diff line number	Diff line change
Expand Up		@@ -313,7 +313,7 @@ extern int _PyDict_CheckConsistency(PyObject *mp, int check_content);
		// Fast inlined version of PyType_HasFeature()
		static inline int
		_PyType_HasFeature(PyTypeObject *type, unsigned long feature) {
		return ((FT_ATOMIC_LOAD_ULONG_RELAXED(type->tp_flags) & feature) != 0);
		return ((type->tp_flags) & feature) != 0;
		}

		extern void _PyType_InitCache(PyInterpreterState *interp);
Expand Down
Original file line number	Diff line number	Diff line change
Expand Up		@@ -134,7 +134,6 @@ extern int _PyType_AddMethod(PyTypeObject , PyMethodDef );
		extern void _PyType_SetFlagsRecursive(PyTypeObject *self, unsigned long mask,
		unsigned long flags);

		extern unsigned int _PyType_GetVersionForCurrentState(PyTypeObject *tp);
		PyAPI_FUNC(void) _PyType_SetVersion(PyTypeObject *tp, unsigned int version);
		PyTypeObject *_PyType_LookupByVersion(unsigned int version);

Expand Down
Original file line number	Diff line number	Diff line change
Expand Up		@@ -620,6 +620,12 @@ given type object has a specified feature.
		#define Py_TPFLAGS_HAVE_FINALIZE (1UL << 0)
		#define Py_TPFLAGS_HAVE_VERSION_TAG (1UL << 18)

		// Flag values for ob_flags (16 bits available, if SIZEOF_VOID_P > 4).
		#define _Py_IMMORTAL_FLAGS (1 << 0)
		#define _Py_STATICALLY_ALLOCATED_FLAG (1 << 2)
		#if defined(Py_GIL_DISABLED) && defined(Py_DEBUG)
		#define _Py_TYPE_REVEALED_FLAG (1 << 3)
		#endif

		#define Py_CONSTANT_NONE 0
		#define Py_CONSTANT_FALSE 1
Expand DownExpand Up		@@ -776,11 +782,7 @@ PyType_HasFeature(PyTypeObject *type, unsigned long feature)
		// PyTypeObject is opaque in the limited C API
		flags = PyType_GetFlags(type);
		#else
		# ifdef Py_GIL_DISABLED
		flags = _Py_atomic_load_ulong_relaxed(&type->tp_flags);
		# else
		flags = type->tp_flags;
		# endif
		flags = type->tp_flags;
		#endif
		return ((flags & feature) != 0);
		}
Expand Down
Original file line number	Diff line number	Diff line change
Expand Up		@@ -19,9 +19,6 @@ immortal. The latter should be the only instances that require
		cleanup during runtime finalization.
		*/

		#define _Py_STATICALLY_ALLOCATED_FLAG 4
		#define _Py_IMMORTAL_FLAGS 1

		#if SIZEOF_VOID_P > 4
		/*
		In 64+ bit systems, any object whose 32 bit reference count is >= 2**31
Expand Down
Original file line number	Diff line number	Diff line change
Expand Up		@@ -4113,6 +4113,32 @@ class E(D):
		else:
		self.fail("shouldn't be able to create inheritance cycles")

		def test_assign_bases_many_subclasses(self):
		class A:
		x = 'hello'
		def __call__(self):
		return 123
		def __getitem__(self, index):
		return None

		class X:
		x = 'bye'

		class B(A):
		pass

		subclasses = []
		for i in range(1000):
		sc = type(f'Sub{i}', (B,), {})
		subclasses.append(sc)

		self.assertEqual(subclasses[0]()(), 123)
		self.assertEqual(subclasses[0]().x, 'hello')
		B.__bases__ = (X,)
		with self.assertRaises(TypeError):
		subclasses[0]()()
		self.assertEqual(subclasses[0]().x, 'bye')

		def test_builtin_bases(self):
		# Make sure all the builtin types can have their base queried without
		# segfaulting. See issue #5787.
Expand Down
Original file line number	Diff line number	Diff line change
Expand Up		@@ -576,6 +576,7 @@ class TestRacesDoNotCrash(TestBase):
		# Careful with these. Bigger numbers have a higher chance of catching bugs,
		# but you can also burn through a ton of type/dict/function versions:
		ITEMS = 1000
		SMALL_ITEMS = 100
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		LOOPS = 4
		WRITERS = 2

Expand DownExpand Up		@@ -619,7 +620,7 @@ class C:
		__getitem__ = lambda self, item: None

		items = []
		for _ in range(self.ITEMS):
		for _ in range(self.SMALL_ITEMS):
		item = C()
		items.append(item)
		return items
Expand DownExpand Up		@@ -790,7 +791,7 @@ class C:
		__getattribute__ = lambda self, name: None

		items = []
		for _ in range(self.ITEMS):
		for _ in range(self.SMALL_ITEMS):
		item = C()
		items.append(item)
		return items
Expand Down
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,6 @@
		In the free-threaded build, avoid data races caused by updating type slots
		or type flags after the type was initially created. For those (typically
		rare) cases, use the stop-the-world mechanism. Remove the use of atomics
		when reading or writing type flags. The use of atomics is not sufficient to
		avoid races (since flags are sometimes read without a lock and without
		atomics) and are no longer required.