gh-103092: Isolate _ctypes, part 1 (#103893)

Establish global state and port the following types to heap types:

- DictRemover_Type
- PyCArg_Type
- PyCThunk_Type
- PyCField_Type
- StructParam_Type

6 files changed, 227 insertions, 195 deletions

diff --git a/Modules/_ctypes/_ctypes.c b/Modules/_ctypes/_ctypes.c
index 6f92ca0..c7ed6bd 100644
--- a/Modules/_ctypes/_ctypes.c
+++ b/Modules/_ctypes/_ctypes.c
@@ -126,6 +126,8 @@ bytes(cdata)
 
 #include "pycore_long.h"          // _PyLong_GetZero()
 
+ctypes_state global_state;
+
 PyObject *PyExc_ArgError = NULL;
 
 /* This dict maps ctypes types to POINTER types */
@@ -150,13 +152,32 @@ typedef struct {
     PyObject *dict;
 } DictRemoverObject;
 
+static int
+_DictRemover_traverse(DictRemoverObject *self, visitproc visit, void *arg)
+{
+    Py_VISIT(Py_TYPE(self));
+    Py_VISIT(self->key);
+    Py_VISIT(self->dict);
+    return 0;
+}
+
+static int
+_DictRemover_clear(DictRemoverObject *self)
+{
+    Py_CLEAR(self->key);
+    Py_CLEAR(self->dict);
+    return 0;
+}
+
 static void
 _DictRemover_dealloc(PyObject *myself)
 {
+    PyTypeObject *tp = Py_TYPE(myself);
     DictRemoverObject *self = (DictRemoverObject *)myself;
-    Py_XDECREF(self->key);
-    Py_XDECREF(self->dict);
-    Py_TYPE(self)->tp_free(myself);
+    PyObject_GC_UnTrack(myself);
+    (void)_DictRemover_clear(self);
+    tp->tp_free(myself);
+    Py_DECREF(tp);
 }
 
 static PyObject *
@@ -173,47 +194,23 @@ _DictRemover_call(PyObject *myself, PyObject *args, PyObject *kw)
     Py_RETURN_NONE;
 }
 
-static PyTypeObject DictRemover_Type = {
-    PyVarObject_HEAD_INIT(NULL, 0)
-    "_ctypes.DictRemover",                      /* tp_name */
-    sizeof(DictRemoverObject),                  /* tp_basicsize */
-    0,                                          /* tp_itemsize */
-    _DictRemover_dealloc,                       /* tp_dealloc */
-    0,                                          /* tp_vectorcall_offset */
-    0,                                          /* tp_getattr */
-    0,                                          /* tp_setattr */
-    0,                                          /* tp_as_async */
-    0,                                          /* tp_repr */
-    0,                                          /* tp_as_number */
-    0,                                          /* tp_as_sequence */
-    0,                                          /* tp_as_mapping */
-    0,                                          /* tp_hash */
-    _DictRemover_call,                          /* tp_call */
-    0,                                          /* tp_str */
-    0,                                          /* tp_getattro */
-    0,                                          /* tp_setattro */
-    0,                                          /* tp_as_buffer */
-/* XXX should participate in GC? */
-    Py_TPFLAGS_DEFAULT,                         /* tp_flags */
-    PyDoc_STR("deletes a key from a dictionary"), /* tp_doc */
-    0,                                          /* tp_traverse */
-    0,                                          /* tp_clear */
-    0,                                          /* tp_richcompare */
-    0,                                          /* tp_weaklistoffset */
-    0,                                          /* tp_iter */
-    0,                                          /* tp_iternext */
-    0,                                          /* tp_methods */
-    0,                                          /* tp_members */
-    0,                                          /* tp_getset */
-    0,                                          /* tp_base */
-    0,                                          /* tp_dict */
-    0,                                          /* tp_descr_get */
-    0,                                          /* tp_descr_set */
-    0,                                          /* tp_dictoffset */
-    0,                                          /* tp_init */
-    0,                                          /* tp_alloc */
-    0,                                          /* tp_new */
-    0,                                          /* tp_free */
+PyDoc_STRVAR(dictremover_doc, "deletes a key from a dictionary");
+
+static PyType_Slot dictremover_slots[] = {
+    {Py_tp_dealloc, _DictRemover_dealloc},
+    {Py_tp_traverse, _DictRemover_traverse},
+    {Py_tp_clear, _DictRemover_clear},
+    {Py_tp_call, _DictRemover_call},
+    {Py_tp_doc, (void *)dictremover_doc},
+    {0, NULL},
+};
+
+static PyType_Spec dictremover_spec = {
+    .name = "_ctypes.DictRemover",
+    .basicsize = sizeof(DictRemoverObject),
+    .flags = (Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC |
+              Py_TPFLAGS_IMMUTABLETYPE),
+    .slots = dictremover_slots,
 };
 
 int
@@ -224,7 +221,8 @@ PyDict_SetItemProxy(PyObject *dict, PyObject *key, PyObject *item)
     PyObject *proxy;
     int result;
 
-    obj = _PyObject_CallNoArgs((PyObject *)&DictRemover_Type);
+    ctypes_state *st = GLOBAL_STATE();
+    obj = _PyObject_CallNoArgs((PyObject *)st->DictRemover_Type);
     if (obj == NULL)
         return -1;
 
@@ -415,23 +413,45 @@ typedef struct {
     PyObject *keep;  // If set, a reference to the original CDataObject.
 } StructParamObject;
 
+static int
+StructParam_traverse(StructParamObject *self, visitproc visit, void *arg)
+{
+    Py_VISIT(Py_TYPE(self));
+    return 0;
+}
+
+static int
+StructParam_clear(StructParamObject *self)
+{
+    Py_CLEAR(self->keep);
+    return 0;
+}
 
 static void
 StructParam_dealloc(PyObject *myself)
 {
     StructParamObject *self = (StructParamObject *)myself;
-    Py_XDECREF(self->keep);
+    PyTypeObject *tp = Py_TYPE(self);
+    PyObject_GC_UnTrack(myself);
+    (void)StructParam_clear(self);
     PyMem_Free(self->ptr);
-    Py_TYPE(self)->tp_free(myself);
+    tp->tp_free(myself);
+    Py_DECREF(tp);
 }
 
+static PyType_Slot structparam_slots[] = {
+    {Py_tp_traverse, StructParam_traverse},
+    {Py_tp_clear, StructParam_clear},
+    {Py_tp_dealloc, StructParam_dealloc},
+    {0, NULL},
+};
 
-static PyTypeObject StructParam_Type = {
-    PyVarObject_HEAD_INIT(NULL, 0)
-    .tp_name = "_ctypes.StructParam_Type",
-    .tp_basicsize = sizeof(StructParamObject),
-    .tp_dealloc = StructParam_dealloc,
-    .tp_flags = Py_TPFLAGS_DEFAULT,
+static PyType_Spec structparam_spec = {
+    .name = "_ctypes.StructParam_Type",
+    .basicsize = sizeof(StructParamObject),
+    .flags = (Py_TPFLAGS_DEFAULT | Py_TPFLAGS_IMMUTABLETYPE |
+              Py_TPFLAGS_HAVE_GC | Py_TPFLAGS_DISALLOW_INSTANTIATION),
+    .slots = structparam_slots,
 };
 
 
@@ -460,7 +480,9 @@ StructUnionType_paramfunc(CDataObject *self)
         /* Create a Python object which calls PyMem_Free(ptr) in
            its deallocator. The object will be destroyed
            at _ctypes_callproc() cleanup. */
-        obj = (&StructParam_Type)->tp_alloc(&StructParam_Type, 0);
+        ctypes_state *st = GLOBAL_STATE();
+        PyTypeObject *tp = st->StructParam_Type;
+        obj = tp->tp_alloc(tp, 0);
         if (obj == NULL) {
             PyMem_Free(ptr);
             return NULL;
@@ -800,7 +822,8 @@ CDataType_from_param(PyObject *type, PyObject *value)
     if (res) {
         return Py_NewRef(value);
     }
-    if (PyCArg_CheckExact(value)) {
+    ctypes_state *st = GLOBAL_STATE();
+    if (PyCArg_CheckExact(st, value)) {
         PyCArgObject *p = (PyCArgObject *)value;
         PyObject *ob = p->obj;
         const char *ob_name;
@@ -1683,7 +1706,8 @@ c_wchar_p_from_param(PyObject *type, PyObject *value)
             return Py_NewRef(value);
         }
     }
-    if (PyCArg_CheckExact(value)) {
+    ctypes_state *st = GLOBAL_STATE();
+    if (PyCArg_CheckExact(st, value)) {
         /* byref(c_char(...)) */
         PyCArgObject *a = (PyCArgObject *)value;
         StgDictObject *dict = PyObject_stgdict(a->obj);
@@ -1746,7 +1770,8 @@ c_char_p_from_param(PyObject *type, PyObject *value)
             return Py_NewRef(value);
         }
     }
-    if (PyCArg_CheckExact(value)) {
+    ctypes_state *st = GLOBAL_STATE();
+    if (PyCArg_CheckExact(st, value)) {
         /* byref(c_char(...)) */
         PyCArgObject *a = (PyCArgObject *)value;
         StgDictObject *dict = PyObject_stgdict(a->obj);
@@ -1847,7 +1872,8 @@ c_void_p_from_param(PyObject *type, PyObject *value)
         return Py_NewRef(value);
     }
 /* byref(...) */
-    if (PyCArg_CheckExact(value)) {
+    ctypes_state *st = GLOBAL_STATE();
+    if (PyCArg_CheckExact(st, value)) {
         /* byref(c_xxx()) */
         PyCArgObject *a = (PyCArgObject *)value;
         if (a->tag == 'P') {
@@ -5635,12 +5661,22 @@ _ctypes_add_types(PyObject *mod)
         } \
     } while (0)
 
+#define CREATE_TYPE(MOD, TP, SPEC) do {                             \
+    PyObject *type = PyType_FromMetaclass(NULL, MOD, SPEC, NULL);   \
+    if (type == NULL) {                                             \
+        return -1;                                                  \
+    }                                                               \
+    TP = (PyTypeObject *)type;                                      \
+} while (0)
+
+    ctypes_state *st = GLOBAL_STATE();
+
     /* Note:
        ob_type is the metatype (the 'type'), defaults to PyType_Type,
        tp_base is the base type, defaults to 'object' aka PyBaseObject_Type.
     */
-    TYPE_READY(&PyCArg_Type);
-    TYPE_READY(&PyCThunk_Type);
+    CREATE_TYPE(mod, st->PyCArg_Type, &carg_spec);
+    CREATE_TYPE(mod, st->PyCThunk_Type, &cthunk_spec);
     TYPE_READY(&PyCData_Type);
     /* StgDict is derived from PyDict_Type */
     TYPE_READY_BASE(&PyCStgDict_Type, &PyDict_Type);
@@ -5673,17 +5709,15 @@ _ctypes_add_types(PyObject *mod)
      * Simple classes
      */
 
-    /* PyCField_Type is derived from PyBaseObject_Type */
-    TYPE_READY(&PyCField_Type);
+    CREATE_TYPE(mod, st->PyCField_Type, &cfield_spec);
 
     /*************************************************
      *
      * Other stuff
      */
 
-    DictRemover_Type.tp_new = PyType_GenericNew;
-    TYPE_READY(&DictRemover_Type);
-    TYPE_READY(&StructParam_Type);
+    CREATE_TYPE(mod, st->DictRemover_Type, &dictremover_spec);
+    CREATE_TYPE(mod, st->StructParam_Type, &structparam_spec);
 
 #ifdef MS_WIN32
     TYPE_READY_BASE(&PyComError_Type, (PyTypeObject*)PyExc_Exception);
@@ -5692,6 +5726,7 @@ _ctypes_add_types(PyObject *mod)
 #undef TYPE_READY
 #undef TYPE_READY_BASE
 #undef MOD_ADD_TYPE
+#undef CREATE_TYPE
     return 0;
 }
 
diff --git a/Modules/_ctypes/callbacks.c b/Modules/_ctypes/callbacks.c
index bc87500..8e694ba 100644
--- a/Modules/_ctypes/callbacks.c
+++ b/Modules/_ctypes/callbacks.c
@@ -28,23 +28,11 @@
 
 /**************************************************************/
 
-static void
-CThunkObject_dealloc(PyObject *myself)
-{
-    CThunkObject *self = (CThunkObject *)myself;
-    PyObject_GC_UnTrack(self);
-    Py_XDECREF(self->converters);
-    Py_XDECREF(self->callable);
-    Py_XDECREF(self->restype);
-    if (self->pcl_write)
-        Py_ffi_closure_free(self->pcl_write);
-    PyObject_GC_Del(self);
-}
-
 static int
 CThunkObject_traverse(PyObject *myself, visitproc visit, void *arg)
 {
     CThunkObject *self = (CThunkObject *)myself;
+    Py_VISIT(Py_TYPE(self));
     Py_VISIT(self->converters);
     Py_VISIT(self->callable);
     Py_VISIT(self->restype);
@@ -61,36 +49,35 @@ CThunkObject_clear(PyObject *myself)
     return 0;
 }
 
-PyTypeObject PyCThunk_Type = {
-    PyVarObject_HEAD_INIT(NULL, 0)
-    "_ctypes.CThunkObject",
-    sizeof(CThunkObject),                       /* tp_basicsize */
-    sizeof(ffi_type),                           /* tp_itemsize */
-    CThunkObject_dealloc,                       /* tp_dealloc */
-    0,                                          /* tp_vectorcall_offset */
-    0,                                          /* tp_getattr */
-    0,                                          /* tp_setattr */
-    0,                                          /* tp_as_async */
-    0,                                          /* tp_repr */
-    0,                                          /* tp_as_number */
-    0,                                          /* tp_as_sequence */
-    0,                                          /* tp_as_mapping */
-    0,                                          /* tp_hash */
-    0,                                          /* tp_call */
-    0,                                          /* tp_str */
-    0,                                          /* tp_getattro */
-    0,                                          /* tp_setattro */
-    0,                                          /* tp_as_buffer */
-    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC,                            /* tp_flags */
-    PyDoc_STR("CThunkObject"),                  /* tp_doc */
-    CThunkObject_traverse,                      /* tp_traverse */
-    CThunkObject_clear,                         /* tp_clear */
-    0,                                          /* tp_richcompare */
-    0,                                          /* tp_weaklistoffset */
-    0,                                          /* tp_iter */
-    0,                                          /* tp_iternext */
-    0,                                          /* tp_methods */
-    0,                                          /* tp_members */
+static void
+CThunkObject_dealloc(PyObject *myself)
+{
+    CThunkObject *self = (CThunkObject *)myself;
+    PyTypeObject *tp = Py_TYPE(myself);
+    PyObject_GC_UnTrack(self);
+    (void)CThunkObject_clear(myself);
+    if (self->pcl_write) {
+        Py_ffi_closure_free(self->pcl_write);
+    }
+    PyObject_GC_Del(self);
+    Py_DECREF(tp);
+}
+
+static PyType_Slot cthunk_slots[] = {
+    {Py_tp_doc, (void *)PyDoc_STR("CThunkObject")},
+    {Py_tp_dealloc, CThunkObject_dealloc},
+    {Py_tp_traverse, CThunkObject_traverse},
+    {Py_tp_clear, CThunkObject_clear},
+    {0, NULL},
+};
+
+PyType_Spec cthunk_spec = {
+    .name = "_ctypes.CThunkObject",
+    .basicsize = sizeof(CThunkObject),
+    .itemsize = sizeof(ffi_type),
+    .flags = (Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC |
+              Py_TPFLAGS_IMMUTABLETYPE | Py_TPFLAGS_DISALLOW_INSTANTIATION),
+    .slots = cthunk_slots,
 };
 
 /**************************************************************/
@@ -320,7 +307,8 @@ static CThunkObject* CThunkObject_new(Py_ssize_t nargs)
     CThunkObject *p;
     Py_ssize_t i;
 
-    p = PyObject_GC_NewVar(CThunkObject, &PyCThunk_Type, nargs);
+    ctypes_state *st = GLOBAL_STATE();
+    p = PyObject_GC_NewVar(CThunkObject, st->PyCThunk_Type, nargs);
     if (p == NULL) {
         return NULL;
     }
@@ -357,7 +345,10 @@ CThunkObject *_ctypes_alloc_callback(PyObject *callable,
     if (p == NULL)
         return NULL;
 
-    assert(CThunk_CheckExact((PyObject *)p));
+#ifdef Py_DEBUG
+    ctypes_state *st = GLOBAL_STATE();
+    assert(CThunk_CheckExact(st, (PyObject *)p));
+#endif
 
     p->pcl_write = Py_ffi_closure_alloc(sizeof(ffi_closure), &p->pcl_exec);
     if (p->pcl_write == NULL) {
diff --git a/Modules/_ctypes/callproc.c b/Modules/_ctypes/callproc.c
index 4438727..93bc784 100644
--- a/Modules/_ctypes/callproc.c
+++ b/Modules/_ctypes/callproc.c
@@ -469,21 +469,41 @@ PyCArgObject *
 PyCArgObject_new(void)
 {
     PyCArgObject *p;
-    p = PyObject_New(PyCArgObject, &PyCArg_Type);
+    ctypes_state *st = GLOBAL_STATE();
+    p = PyObject_GC_New(PyCArgObject, st->PyCArg_Type);
     if (p == NULL)
         return NULL;
     p->pffi_type = NULL;
     p->tag = '\0';
     p->obj = NULL;
     memset(&p->value, 0, sizeof(p->value));
+    PyObject_GC_Track(p);
     return p;
 }
 
+static int
+PyCArg_traverse(PyCArgObject *self, visitproc visit, void *arg)
+{
+    Py_VISIT(Py_TYPE(self));
+    Py_VISIT(self->obj);
+    return 0;
+}
+
+static int
+PyCArg_clear(PyCArgObject *self)
+{
+    Py_CLEAR(self->obj);
+    return 0;
+}
+
 static void
 PyCArg_dealloc(PyCArgObject *self)
 {
-    Py_XDECREF(self->obj);
-    PyObject_Free(self);
+    PyTypeObject *tp = Py_TYPE(self);
+    PyObject_GC_UnTrack(self);
+    (void)PyCArg_clear(self);
+    tp->tp_free((PyObject *)self);
+    Py_DECREF(tp);
 }
 
 static int
@@ -567,36 +587,21 @@ static PyMemberDef PyCArgType_members[] = {
     { NULL },
 };
 
-PyTypeObject PyCArg_Type = {
-    PyVarObject_HEAD_INIT(NULL, 0)
-    "CArgObject",
-    sizeof(PyCArgObject),
-    0,
-    (destructor)PyCArg_dealloc,                 /* tp_dealloc */
-    0,                                          /* tp_vectorcall_offset */
-    0,                                          /* tp_getattr */
-    0,                                          /* tp_setattr */
-    0,                                          /* tp_as_async */
-    (reprfunc)PyCArg_repr,                      /* tp_repr */
-    0,                                          /* tp_as_number */
-    0,                                          /* tp_as_sequence */
-    0,                                          /* tp_as_mapping */
-    0,                                          /* tp_hash */
-    0,                                          /* tp_call */
-    0,                                          /* tp_str */
-    0,                                          /* tp_getattro */
-    0,                                          /* tp_setattro */
-    0,                                          /* tp_as_buffer */
-    Py_TPFLAGS_DEFAULT,                         /* tp_flags */
-    0,                                          /* tp_doc */
-    0,                                          /* tp_traverse */
-    0,                                          /* tp_clear */
-    0,                                          /* tp_richcompare */
-    0,                                          /* tp_weaklistoffset */
-    0,                                          /* tp_iter */
-    0,                                          /* tp_iternext */
-    0,                                          /* tp_methods */
-    PyCArgType_members,                         /* tp_members */
+static PyType_Slot carg_slots[] = {
+    {Py_tp_dealloc, PyCArg_dealloc},
+    {Py_tp_traverse, PyCArg_traverse},
+    {Py_tp_clear, PyCArg_clear},
+    {Py_tp_repr, PyCArg_repr},
+    {Py_tp_members, PyCArgType_members},
+    {0, NULL},
+};
+
+PyType_Spec carg_spec = {
+    .name = "_ctypes.CArgObject",
+    .basicsize = sizeof(PyCArgObject),
+    .flags = (Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC |
+              Py_TPFLAGS_IMMUTABLETYPE | Py_TPFLAGS_DISALLOW_INSTANTIATION),
+    .slots = carg_slots,
 };
 
 /****************************************************************/
@@ -669,7 +674,8 @@ static int ConvParam(PyObject *obj, Py_ssize_t index, struct argument *pa)
         return 0;
     }
 
-    if (PyCArg_CheckExact(obj)) {
+    ctypes_state *st = GLOBAL_STATE();
+    if (PyCArg_CheckExact(st, obj)) {
         PyCArgObject *carg = (PyCArgObject *)obj;
         pa->ffi_type = carg->pffi_type;
         pa->keep = Py_NewRef(obj);
diff --git a/Modules/_ctypes/cfield.c b/Modules/_ctypes/cfield.c
index 796a1be..128506a 100644
--- a/Modules/_ctypes/cfield.c
+++ b/Modules/_ctypes/cfield.c
@@ -61,7 +61,9 @@ PyCField_FromDesc(PyObject *desc, Py_ssize_t index,
 #define CONT_BITFIELD 2
 #define EXPAND_BITFIELD 3
 
-    self = (CFieldObject *)PyCField_Type.tp_alloc((PyTypeObject *)&PyCField_Type, 0);
+    ctypes_state *st = GLOBAL_STATE();
+    PyTypeObject *tp = st->PyCField_Type;
+    self = (CFieldObject *)tp->tp_alloc(tp, 0);
     if (self == NULL)
         return NULL;
     dict = PyType_stgdict(desc);
@@ -256,6 +258,7 @@ static PyGetSetDef PyCField_getset[] = {
 static int
 PyCField_traverse(CFieldObject *self, visitproc visit, void *arg)
 {
+    Py_VISIT(Py_TYPE(self));
     Py_VISIT(self->proto);
     return 0;
 }
@@ -270,9 +273,11 @@ PyCField_clear(CFieldObject *self)
 static void
 PyCField_dealloc(PyObject *self)
 {
+    PyTypeObject *tp = Py_TYPE(self);
     PyObject_GC_UnTrack(self);
-    PyCField_clear((CFieldObject *)self);
+    (void)PyCField_clear((CFieldObject *)self);
     Py_TYPE(self)->tp_free((PyObject *)self);
+    Py_DECREF(tp);
 }
 
 static PyObject *
@@ -296,46 +301,24 @@ PyCField_repr(CFieldObject *self)
     return result;
 }
 
-PyTypeObject PyCField_Type = {
-    PyVarObject_HEAD_INIT(NULL, 0)
-    "_ctypes.CField",                                   /* tp_name */
-    sizeof(CFieldObject),                       /* tp_basicsize */
-    0,                                          /* tp_itemsize */
-    PyCField_dealloc,                                   /* tp_dealloc */
-    0,                                          /* tp_vectorcall_offset */
-    0,                                          /* tp_getattr */
-    0,                                          /* tp_setattr */
-    0,                                          /* tp_as_async */
-    (reprfunc)PyCField_repr,                            /* tp_repr */
-    0,                                          /* tp_as_number */
-    0,                                          /* tp_as_sequence */
-    0,                                          /* tp_as_mapping */
-    0,                                          /* tp_hash */
-    0,                                          /* tp_call */
-    0,                                          /* tp_str */
-    0,                                          /* tp_getattro */
-    0,                                          /* tp_setattro */
-    0,                                          /* tp_as_buffer */
-    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC, /* tp_flags */
-    PyDoc_STR("Structure/Union member"),        /* tp_doc */
-    (traverseproc)PyCField_traverse,                    /* tp_traverse */
-    (inquiry)PyCField_clear,                            /* tp_clear */
-    0,                                          /* tp_richcompare */
-    0,                                          /* tp_weaklistoffset */
-    0,                                          /* tp_iter */
-    0,                                          /* tp_iternext */
-    0,                                          /* tp_methods */
-    0,                                          /* tp_members */
-    PyCField_getset,                                    /* tp_getset */
-    0,                                          /* tp_base */
-    0,                                          /* tp_dict */
-    (descrgetfunc)PyCField_get,                 /* tp_descr_get */
-    (descrsetfunc)PyCField_set,                 /* tp_descr_set */
-    0,                                          /* tp_dictoffset */
-    0,                                          /* tp_init */
-    0,                                          /* tp_alloc */
-    0,                                          /* tp_new */
-    0,                                          /* tp_free */
+static PyType_Slot cfield_slots[] = {
+    {Py_tp_dealloc, PyCField_dealloc},
+    {Py_tp_repr, PyCField_repr},
+    {Py_tp_doc, (void *)PyDoc_STR("Structure/Union member")},
+    {Py_tp_traverse, PyCField_traverse},
+    {Py_tp_clear, PyCField_clear},
+    {Py_tp_getset, PyCField_getset},
+    {Py_tp_descr_get, PyCField_get},
+    {Py_tp_descr_set, PyCField_set},
+    {0, NULL},
+};
+
+PyType_Spec cfield_spec = {
+    .name = "_ctypes.CField",
+    .basicsize = sizeof(CFieldObject),
+    .flags = (Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC |
+              Py_TPFLAGS_IMMUTABLETYPE | Py_TPFLAGS_DISALLOW_INSTANTIATION),
+    .slots = cfield_slots,
 };
 
 
diff --git a/Modules/_ctypes/ctypes.h b/Modules/_ctypes/ctypes.h
index a7029b6..252d9da 100644
--- a/Modules/_ctypes/ctypes.h
+++ b/Modules/_ctypes/ctypes.h
@@ -32,6 +32,22 @@
 #endif
 #endif
 
+typedef struct {
+    PyTypeObject *DictRemover_Type;
+    PyTypeObject *PyCArg_Type;
+    PyTypeObject *PyCField_Type;
+    PyTypeObject *PyCThunk_Type;
+    PyTypeObject *StructParam_Type;
+} ctypes_state;
+
+extern ctypes_state global_state;
+
+#define GLOBAL_STATE() (&global_state)
+
+extern PyType_Spec carg_spec;
+extern PyType_Spec cfield_spec;
+extern PyType_Spec cthunk_spec;
+
 typedef struct tagPyCArgObject PyCArgObject;
 typedef struct tagCDataObject CDataObject;
 typedef PyObject *(* GETFUNC)(void *, Py_ssize_t size);
@@ -88,8 +104,7 @@ typedef struct {
     ffi_type *ffi_restype;
     ffi_type *atypes[1];
 } CThunkObject;
-extern PyTypeObject PyCThunk_Type;
-#define CThunk_CheckExact(v)        Py_IS_TYPE(v, &PyCThunk_Type)
+#define CThunk_CheckExact(st, v)        Py_IS_TYPE(v, st->PyCThunk_Type)
 
 typedef struct {
     /* First part identical to tagCDataObject */
@@ -141,7 +156,6 @@ extern PyTypeObject PyCSimpleType_Type;
 #define PyCSimpleTypeObject_CheckExact(v)       Py_IS_TYPE(v, &PyCSimpleType_Type)
 #define PyCSimpleTypeObject_Check(v)    PyObject_TypeCheck(v, &PyCSimpleType_Type)
 
-extern PyTypeObject PyCField_Type;
 extern struct fielddesc *_ctypes_get_fielddesc(const char *fmt);
 
 
@@ -334,8 +348,7 @@ struct tagPyCArgObject {
     Py_ssize_t size; /* for the 'V' tag */
 };
 
-extern PyTypeObject PyCArg_Type;
-#define PyCArg_CheckExact(v)        Py_IS_TYPE(v, &PyCArg_Type)
+#define PyCArg_CheckExact(st, v)        Py_IS_TYPE(v, st->PyCArg_Type)
 extern PyCArgObject *PyCArgObject_new(void);
 
 extern PyObject *
diff --git a/Modules/_ctypes/stgdict.c b/Modules/_ctypes/stgdict.c
index 83a5275..b1b2bac 100644
--- a/Modules/_ctypes/stgdict.c
+++ b/Modules/_ctypes/stgdict.c
@@ -225,6 +225,8 @@ MakeFields(PyObject *type, CFieldObject *descr,
     if (fieldlist == NULL)
         return -1;
 
+    ctypes_state *st = GLOBAL_STATE();
+    PyTypeObject *cfield_tp = st->PyCField_Type;
     for (i = 0; i < PySequence_Fast_GET_SIZE(fieldlist); ++i) {
         PyObject *pair = PySequence_Fast_GET_ITEM(fieldlist, i); /* borrowed */
         PyObject *fname, *ftype, *bits;
@@ -240,7 +242,7 @@ MakeFields(PyObject *type, CFieldObject *descr,
             Py_DECREF(fieldlist);
             return -1;
         }
-        if (!Py_IS_TYPE(fdescr, &PyCField_Type)) {
+        if (!Py_IS_TYPE(fdescr, cfield_tp)) {
             PyErr_SetString(PyExc_TypeError, "unexpected type");
             Py_DECREF(fdescr);
             Py_DECREF(fieldlist);
@@ -257,13 +259,13 @@ MakeFields(PyObject *type, CFieldObject *descr,
             }
             continue;
         }
-        new_descr = (CFieldObject *)PyCField_Type.tp_alloc((PyTypeObject *)&PyCField_Type, 0);
+        new_descr = (CFieldObject *)cfield_tp->tp_alloc(cfield_tp, 0);
         if (new_descr == NULL) {
             Py_DECREF(fdescr);
             Py_DECREF(fieldlist);
             return -1;
         }
-        assert(Py_IS_TYPE(new_descr, &PyCField_Type));
+        assert(Py_IS_TYPE(new_descr, cfield_tp));
         new_descr->size = fdescr->size;
         new_descr->offset = fdescr->offset + offset;
         new_descr->index = fdescr->index + index;
@@ -304,6 +306,8 @@ MakeAnonFields(PyObject *type)
     if (anon_names == NULL)
         return -1;
 
+    ctypes_state *st = GLOBAL_STATE();
+    PyTypeObject *cfield_tp = st->PyCField_Type;
     for (i = 0; i < PySequence_Fast_GET_SIZE(anon_names); ++i) {
         PyObject *fname = PySequence_Fast_GET_ITEM(anon_names, i); /* borrowed */
         CFieldObject *descr = (CFieldObject *)PyObject_GetAttr(type, fname);
@@ -311,7 +315,7 @@ MakeAnonFields(PyObject *type)
             Py_DECREF(anon_names);
             return -1;
         }
-        if (!Py_IS_TYPE(descr, &PyCField_Type)) {
+        if (!Py_IS_TYPE(descr, cfield_tp)) {
             PyErr_Format(PyExc_AttributeError,
                          "'%U' is specified in _anonymous_ but not in "
                          "_fields_",