Implemented circular references traversal for Boost.Python.instance o…

…bjects.

src/core/sp_python.cpp

@@ -56,6 +56,7 @@ CPythonManager g_PythonManager;
 // Forward declarations.
 //---------------------------------------------------------------------------------
 void InitConverters();
+void EnableDictTraversal();
 
 
 //---------------------------------------------------------------------------------
@@ -168,6 +169,9 @@ bool CPythonManager::Initialize( void )
 	// And of course, the plugins directory for script imports.
 	AddToSysPath("/plugins");
 
+	// Enable circular references traversal
+	EnableDictTraversal();
+
 	// Initialize all converters
 	InitConverters();
 
@@ -262,6 +266,39 @@ bool CPythonManager::Shutdown( void )
 }
 
 
+//---------------------------------------------------------------------------------
+// Circular references traversal
+//---------------------------------------------------------------------------------
+struct dict_traversal
+{
+	static int is_gc(PyObject *self)
+	{
+		return !!downcast<objects::instance<> >(self)->dict;
+	}
+
+	static int traverse(PyObject *self, visitproc visit, void *arg)
+	{
+		Py_VISIT(downcast<objects::instance<> >(self)->dict);
+		return 0;
+	}
+
+	static int clear(PyObject *self)
+	{
+		Py_CLEAR(downcast<objects::instance<> >(self)->dict);
+		return 0;
+	}
+};
+
+void EnableDictTraversal()
+{
+	PyTypeObject *type = objects::class_type().get();
+	type->tp_flags |= Py_TPFLAGS_HAVE_GC;
+	type->tp_is_gc = dict_traversal::is_gc;
+	type->tp_traverse = dict_traversal::traverse;
+	type->tp_clear = dict_traversal::clear;
+}
+
+
 //---------------------------------------------------------------------------------
 // Converters
 //---------------------------------------------------------------------------------