gh-100926: use explicit stginfo lock for pointer cache (#133867)

Author: kumaraditya303

Modules/_ctypes/_ctypes.c

@@ -578,14 +578,13 @@ _ctypes_CType_Type___sizeof___impl(PyObject *self, PyTypeObject *cls)
 
 /*[clinic input]
 @getter
-@critical_section
 _ctypes.CType_Type.__pointer_type__
 
 [clinic start generated code]*/
 
 static PyObject *
 _ctypes_CType_Type___pointer_type___get_impl(PyObject *self)
-/*[clinic end generated code: output=718c9ff10b2b0012 input=ff7498aa6edf487c]*/
+/*[clinic end generated code: output=718c9ff10b2b0012 input=ad12dc835943ceb8]*/
 {
     ctypes_state *st = get_module_state_by_def(Py_TYPE(self));
     StgInfo *info;
@@ -596,9 +595,12 @@ _ctypes_CType_Type___pointer_type___get_impl(PyObject *self)
         PyErr_Format(PyExc_TypeError, "%R must have storage info", self);
         return NULL;
     }
-
-    if (info->pointer_type) {
-        return Py_NewRef(info->pointer_type);
+    PyObject *pointer_type;
+    STGINFO_LOCK(info);
+    pointer_type = Py_XNewRef(info->pointer_type);
+    STGINFO_UNLOCK();
+    if (pointer_type) {
+        return pointer_type;
     }
 
     PyErr_Format(PyExc_AttributeError,
@@ -609,14 +611,13 @@ _ctypes_CType_Type___pointer_type___get_impl(PyObject *self)
 
 /*[clinic input]
 @setter
-@critical_section
 _ctypes.CType_Type.__pointer_type__
 
 [clinic start generated code]*/
 
 static int
 _ctypes_CType_Type___pointer_type___set_impl(PyObject *self, PyObject *value)
-/*[clinic end generated code: output=6259be8ea21693fa input=9b2dc2400c388982]*/
+/*[clinic end generated code: output=6259be8ea21693fa input=a05055fc7f4714b6]*/
 {
     ctypes_state *st = get_module_state_by_def(Py_TYPE(self));
     StgInfo *info;
@@ -627,8 +628,9 @@ _ctypes_CType_Type___pointer_type___set_impl(PyObject *self, PyObject *value)
         PyErr_Format(PyExc_TypeError, "%R must have storage info", self);
         return -1;
     }
-
+    STGINFO_LOCK(info);
     Py_XSETREF(info->pointer_type, Py_XNewRef(value));
+    STGINFO_UNLOCK();
     return 0;
 }