Test if PyCStgInfo_clone not share pointer_type cache

Author: sergey-miryanov

Lib/test/test_ctypes/test_structures.py

@@ -644,6 +644,30 @@ class Test8(Union):
         self.assertEqual(ctx.exception.args[0], 'item 1 in _argtypes_ passes '
                          'a union by value, which is unsupported.')
 
+    def test_do_not_share_pointer_type_cache_via_stginfo_clone(self):
+        # This test case calls PyCStgInfo_clone()
+        # for the Mid and Vector class definitions
+        # and checks that pointer_type cache not shared
+        # between subclasses.
+        class Base(Structure):
+            _fields_ = [('y', c_double),
+                        ('x', c_double)]
+        base_ptr = POINTER(Base)
+
+        class Mid(Base):
+            pass
+        Mid._fields_ = []
+        mid_ptr = POINTER(Mid)
+
+        class Vector(Mid):
+            pass
+
+        vector_ptr = POINTER(Vector)
+
+        self.assertIsNot(base_ptr, mid_ptr)
+        self.assertIsNot(base_ptr, vector_ptr)
+        self.assertIsNot(mid_ptr, vector_ptr)
+
 
 if __name__ == '__main__':
     unittest.main()

Modules/_ctypes/_ctypes.c

@@ -494,6 +494,20 @@ ctype_clear_stginfo(StgInfo *info)
     Py_CLEAR(info->module);  // decref the module last
 }
 
+void
+ctype_free_stginfo_members(StgInfo *info)
+{
+    assert(info);
+
+    PyMem_Free(info->ffi_type_pointer.elements);
+    info->ffi_type_pointer.elements = NULL;
+    PyMem_Free(info->format);
+    info->format = NULL;
+    PyMem_Free(info->shape);
+    info->shape = NULL;
+    ctype_clear_stginfo(info);
+}
+
 static int
 CType_Type_clear(PyObject *self)
 {
@@ -517,13 +531,7 @@ CType_Type_dealloc(PyObject *self)
                                "deallocating ctypes %R", self);
     }
     if (info) {
-        PyMem_Free(info->ffi_type_pointer.elements);
-        info->ffi_type_pointer.elements = NULL;
-        PyMem_Free(info->format);
-        info->format = NULL;
-        PyMem_Free(info->shape);
-        info->shape = NULL;
-        ctype_clear_stginfo(info);
+        ctype_free_stginfo_members(info);
     }
 
     PyTypeObject *tp = Py_TYPE(self);

Modules/_ctypes/ctypes.h

@@ -378,6 +378,7 @@ typedef struct {
 
 extern int PyCStgInfo_clone(StgInfo *dst_info, StgInfo *src_info);
 extern void ctype_clear_stginfo(StgInfo *info);
+extern void ctype_free_stginfo_members(StgInfo *info);
 
 typedef int(* PPROC)(void);
 

Modules/_ctypes/stgdict.c

@@ -25,13 +25,7 @@ PyCStgInfo_clone(StgInfo *dst_info, StgInfo *src_info)
 {
     Py_ssize_t size;
 
-    ctype_clear_stginfo(dst_info);
-    PyMem_Free(dst_info->ffi_type_pointer.elements);
-    PyMem_Free(dst_info->format);
-    dst_info->format = NULL;
-    PyMem_Free(dst_info->shape);
-    dst_info->shape = NULL;
-    dst_info->ffi_type_pointer.elements = NULL;
+    ctype_free_stginfo_members(dst_info);
 
     memcpy(dst_info, src_info, sizeof(StgInfo));
 
@@ -40,8 +34,8 @@ PyCStgInfo_clone(StgInfo *dst_info, StgInfo *src_info)
     Py_XINCREF(dst_info->converters);
     Py_XINCREF(dst_info->restype);
     Py_XINCREF(dst_info->checker);
-    dst_info->pointer_type = NULL;  // the cache cannot be shared
     Py_XINCREF(dst_info->module);
+    dst_info->pointer_type = NULL;  // the cache cannot be shared
 
     if (src_info->format) {
         dst_info->format = PyMem_Malloc(strlen(src_info->format) + 1);