gh-105020: Share tp_bases and tp_mro Between Interpreters For All Static Builtin Types (gh-105115)

In gh-103912 we added tp_bases and tp_mro to each PyInterpreterState.types.builtins entry.  However, doing so ignored the fact that both PyTypeObject fields are public API, and not documented as internal (as opposed to tp_subclasses).  We address that here by reverting back to shared objects, making them immortal in the process.

Include/internal/pycore_object.h

@@ -76,6 +76,21 @@ static inline void _Py_SetImmortal(PyObject *op)
 }
 #define _Py_SetImmortal(op) _Py_SetImmortal(_PyObject_CAST(op))
 
+/* _Py_ClearImmortal() should only be used during runtime finalization. */
+static inline void _Py_ClearImmortal(PyObject *op)
+{
+    if (op) {
+        assert(op->ob_refcnt == _Py_IMMORTAL_REFCNT);
+        op->ob_refcnt = 1;
+        Py_DECREF(op);
+    }
+}
+#define _Py_ClearImmortal(op) \
+    do { \
+        _Py_ClearImmortal(_PyObject_CAST(op)); \
+        op = NULL; \
+    } while (0)
+
 static inline void
 _Py_DECREF_SPECIALIZED(PyObject *op, const destructor destruct)
 {

Include/internal/pycore_typeobject.h

@@ -46,11 +46,9 @@ typedef struct {
     PyTypeObject *type;
     int readying;
     int ready;
-    // XXX tp_dict, tp_bases, and tp_mro can probably be statically
+    // XXX tp_dict can probably be statically allocated,
-    // allocated, instead of dynamically and stored on the interpreter.
+    // instead of dynamically and stored on the interpreter.
     PyObject *tp_dict;
-    PyObject *tp_bases;
-    PyObject *tp_mro;
     PyObject *tp_subclasses;
     /* We never clean up weakrefs for static builtin types since
        they will effectively never get triggered.  However, there

Lib/test/test_capi/test_misc.py

@@ -1593,6 +1593,39 @@ class SubinterpreterTest(unittest.TestCase):
         self.assertEqual(main_attr_id, subinterp_attr_id)
 
 
+class BuiltinStaticTypesTests(unittest.TestCase):
+
+    TYPES = [
+        object,
+        type,
+        int,
+        str,
+        dict,
+        type(None),
+        bool,
+        BaseException,
+        Exception,
+        Warning,
+        DeprecationWarning,  # Warning subclass
+    ]
+
+    def test_tp_bases_is_set(self):
+        # PyTypeObject.tp_bases is documented as public API.
+        # See https://github.com/python/cpython/issues/105020.
+        for typeobj in self.TYPES:
+            with self.subTest(typeobj):
+                bases = _testcapi.type_get_tp_bases(typeobj)
+                self.assertIsNot(bases, None)
+
+    def test_tp_mro_is_set(self):
+        # PyTypeObject.tp_bases is documented as public API.
+        # See https://github.com/python/cpython/issues/105020.
+        for typeobj in self.TYPES:
+            with self.subTest(typeobj):
+                mro = _testcapi.type_get_tp_mro(typeobj)
+                self.assertIsNot(mro, None)
+
+
 class TestThreadState(unittest.TestCase):
 
     @threading_helper.reap_threads

Misc/NEWS.d/next/C API/2023-05-30-17-45-32.gh-issue-105115.iRho1K.rst

@@ -0,0 +1,3 @@
+``PyTypeObject.tp_bases`` (and ``tp_mro``) for builtin static types are now
+shared by all interpreters, whereas in 3.12-beta1 they were stored on
+``PyInterpreterState``.  Also note that now the tuples are immortal objects.

Modules/_testcapimodule.c

@@ -2606,6 +2606,27 @@ type_assign_version(PyObject *self, PyObject *type)
 }
 
 
+static PyObject *
+type_get_tp_bases(PyObject *self, PyObject *type)
+{
+    PyObject *bases = ((PyTypeObject *)type)->tp_bases;
+    if (bases == NULL) {
+        Py_RETURN_NONE;
+    }
+    return Py_NewRef(bases);
+}
+
+static PyObject *
+type_get_tp_mro(PyObject *self, PyObject *type)
+{
+    PyObject *mro = ((PyTypeObject *)type)->tp_mro;
+    if (mro == NULL) {
+        Py_RETURN_NONE;
+    }
+    return Py_NewRef(mro);
+}
+
+
 // Test PyThreadState C API
 static PyObject *
 test_tstate_capi(PyObject *self, PyObject *Py_UNUSED(args))
@@ -3361,6 +3382,8 @@ static PyMethodDef TestMethods[] = {
     {"test_py_is_funcs", test_py_is_funcs, METH_NOARGS},
     {"type_get_version", type_get_version, METH_O, PyDoc_STR("type->tp_version_tag")},
     {"type_assign_version", type_assign_version, METH_O, PyDoc_STR("PyUnstable_Type_AssignVersionTag")},
+    {"type_get_tp_bases", type_get_tp_bases, METH_O},
+    {"type_get_tp_mro", type_get_tp_mro, METH_O},
     {"test_tstate_capi", test_tstate_capi, METH_NOARGS, NULL},
     {"frame_getlocals", frame_getlocals, METH_O, NULL},
     {"frame_getglobals", frame_getglobals, METH_O, NULL},

Objects/typeobject.c

@@ -268,12 +268,6 @@ clear_tp_dict(PyTypeObject *self)
 static inline PyObject *
 lookup_tp_bases(PyTypeObject *self)
 {
-    if (self->tp_flags & _Py_TPFLAGS_STATIC_BUILTIN) {
-        PyInterpreterState *interp = _PyInterpreterState_GET();
-        static_builtin_state *state = _PyStaticType_GetState(interp, self);
-        assert(state != NULL);
-        return state->tp_bases;
-    }
     return self->tp_bases;
 }
 
@@ -287,12 +281,22 @@ _PyType_GetBases(PyTypeObject *self)
 static inline void
 set_tp_bases(PyTypeObject *self, PyObject *bases)
 {
+    assert(PyTuple_CheckExact(bases));
     if (self->tp_flags & _Py_TPFLAGS_STATIC_BUILTIN) {
-        PyInterpreterState *interp = _PyInterpreterState_GET();
+        // XXX tp_bases can probably be statically allocated for each
-        static_builtin_state *state = _PyStaticType_GetState(interp, self);
+        // static builtin type.
-        assert(state != NULL);
+        assert(_Py_IsMainInterpreter(_PyInterpreterState_GET()));
-        state->tp_bases = bases;
+        assert(self->tp_bases == NULL);
-        return;
+        if (PyTuple_GET_SIZE(bases) == 0) {
+            assert(self->tp_base == NULL);
+        }
+        else {
+            assert(PyTuple_GET_SIZE(bases) == 1);
+            assert(PyTuple_GET_ITEM(bases, 0) == (PyObject *)self->tp_base);
+            assert(self->tp_base->tp_flags & _Py_TPFLAGS_STATIC_BUILTIN);
+            assert(_Py_IsImmortal(self->tp_base));
+        }
+        _Py_SetImmortal(bases);
     }
     self->tp_bases = bases;
 }
@@ -301,10 +305,14 @@ static inline void
 clear_tp_bases(PyTypeObject *self)
 {
     if (self->tp_flags & _Py_TPFLAGS_STATIC_BUILTIN) {
-        PyInterpreterState *interp = _PyInterpreterState_GET();
+        if (_Py_IsMainInterpreter(_PyInterpreterState_GET())) {
-        static_builtin_state *state = _PyStaticType_GetState(interp, self);
+            if (self->tp_bases != NULL
-        assert(state != NULL);
+                && PyTuple_GET_SIZE(self->tp_bases) > 0)
-        Py_CLEAR(state->tp_bases);
+            {
+                assert(_Py_IsImmortal(self->tp_bases));
+                _Py_ClearImmortal(self->tp_bases);
+            }
+        }
         return;
     }
     Py_CLEAR(self->tp_bases);
@@ -314,12 +322,6 @@ clear_tp_bases(PyTypeObject *self)
 static inline PyObject *
 lookup_tp_mro(PyTypeObject *self)
 {
-    if (self->tp_flags & _Py_TPFLAGS_STATIC_BUILTIN) {
-        PyInterpreterState *interp = _PyInterpreterState_GET();
-        static_builtin_state *state = _PyStaticType_GetState(interp, self);
-        assert(state != NULL);
-        return state->tp_mro;
-    }
     return self->tp_mro;
 }
 
@@ -333,12 +335,14 @@ _PyType_GetMRO(PyTypeObject *self)
 static inline void
 set_tp_mro(PyTypeObject *self, PyObject *mro)
 {
+    assert(PyTuple_CheckExact(mro));
     if (self->tp_flags & _Py_TPFLAGS_STATIC_BUILTIN) {
-        PyInterpreterState *interp = _PyInterpreterState_GET();
+        // XXX tp_mro can probably be statically allocated for each
-        static_builtin_state *state = _PyStaticType_GetState(interp, self);
+        // static builtin type.
-        assert(state != NULL);
+        assert(_Py_IsMainInterpreter(_PyInterpreterState_GET()));
-        state->tp_mro = mro;
+        assert(self->tp_mro == NULL);
-        return;
+        /* Other checks are done via set_tp_bases. */
+        _Py_SetImmortal(mro);
     }
     self->tp_mro = mro;
 }
@@ -347,10 +351,14 @@ static inline void
 clear_tp_mro(PyTypeObject *self)
 {
     if (self->tp_flags & _Py_TPFLAGS_STATIC_BUILTIN) {
-        PyInterpreterState *interp = _PyInterpreterState_GET();
+        if (_Py_IsMainInterpreter(_PyInterpreterState_GET())) {
-        static_builtin_state *state = _PyStaticType_GetState(interp, self);
+            if (self->tp_mro != NULL
-        assert(state != NULL);
+                && PyTuple_GET_SIZE(self->tp_mro) > 0)
-        Py_CLEAR(state->tp_mro);
+            {
+                assert(_Py_IsImmortal(self->tp_mro));
+                _Py_ClearImmortal(self->tp_mro);
+            }
+        }
         return;
     }
     Py_CLEAR(self->tp_mro);
@@ -7153,6 +7161,14 @@ type_ready_preheader(PyTypeObject *type)
 static int
 type_ready_mro(PyTypeObject *type)
 {
+    if (type->tp_flags & _Py_TPFLAGS_STATIC_BUILTIN) {
+        if (!_Py_IsMainInterpreter(_PyInterpreterState_GET())) {
+            assert(lookup_tp_mro(type) != NULL);
+            return 0;
+        }
+        assert(lookup_tp_mro(type) == NULL);
+    }
+
     /* Calculate method resolution order */
     if (mro_internal(type, NULL) < 0) {
         return -1;