Refactor locking in setSuperclass.

Now all lock ownership is tied to scopes, so will be released correctly
in all return paths.

runtime.c

@@ -522,58 +522,54 @@ Class class_setSuperclass(Class cls, Class newSuper)
 {
 	CHECK_ARG(cls);
 	CHECK_ARG(newSuper);
+	Class oldSuper;
 	if (Nil == cls) { return Nil; }
 
-	LOCK_RUNTIME();
+	{
+		LOCK_RUNTIME_FOR_SCOPE();
 
-	if (cls->super_class == newSuper) {
-		UNLOCK_RUNTIME();
-		return newSuper;
-	}
+		oldSuper = cls->super_class;
 
-	safe_remove_from_subclass_list(cls);
-	objc_resolve_class(newSuper);
+		if (oldSuper == newSuper) { return newSuper; }
 
-	Class oldSuper = cls->super_class;
-	cls->super_class = newSuper;
+		safe_remove_from_subclass_list(cls);
+		objc_resolve_class(newSuper);
 
-	// The super class's subclass list is used in certain method resolution scenarios.
-	cls->sibling_class = cls->super_class->subclass_list;
-	cls->super_class->subclass_list = cls;
+		cls->super_class = newSuper;
 
-	if (UNLIKELY(class_isMetaClass(cls)))
-	{
-		// newSuper is presumably a metaclass. Its isa will therefore be the appropriate root metaclass.
-		cls->isa = newSuper->isa;
-	}
-	else
-	{
-		Class meta = cls->isa, newSuperMeta = newSuper->isa;
-		// Update the metaclass's superclass.
-		safe_remove_from_subclass_list(meta);
-		objc_resolve_class(newSuperMeta);
+		// The super class's subclass list is used in certain method resolution scenarios.
+		cls->sibling_class = cls->super_class->subclass_list;
+		cls->super_class->subclass_list = cls;
+
+		if (UNLIKELY(class_isMetaClass(cls)))
+		{
+			// newSuper is presumably a metaclass. Its isa will therefore be the appropriate root metaclass.
+			cls->isa = newSuper->isa;
+		}
+		else
+		{
+			Class meta = cls->isa, newSuperMeta = newSuper->isa;
+			// Update the metaclass's superclass.
+			safe_remove_from_subclass_list(meta);
+			objc_resolve_class(newSuperMeta);
 
-		meta->super_class = newSuperMeta;
-		meta->isa = newSuperMeta->isa;
+			meta->super_class = newSuperMeta;
+			meta->isa = newSuperMeta->isa;
 
-		// The super class's subclass list is used in certain method resolution scenarios.
-		meta->sibling_class = newSuperMeta->subclass_list;
-		newSuperMeta->subclass_list = meta;
-	}
+			// The super class's subclass list is used in certain method resolution scenarios.
+			meta->sibling_class = newSuperMeta->subclass_list;
+			newSuperMeta->subclass_list = meta;
+		}
 
-	LOCK(&initialize_lock);
-	if (!objc_test_class_flag(cls, objc_class_flag_initialized))
-	{
-		// Uninitialized classes don't have dtables to update
-		// and don't need their superclasses initialized.
-		UNLOCK(&initialize_lock);
-		UNLOCK_RUNTIME();
-		return oldSuper;
+		LOCK_FOR_SCOPE(&initialize_lock);
+		if (!objc_test_class_flag(cls, objc_class_flag_initialized))
+		{
+			// Uninitialized classes don't have dtables to update
+			// and don't need their superclasses initialized.
+			return oldSuper;
+		}
 	}
 
-	UNLOCK(&initialize_lock);
-	UNLOCK_RUNTIME();
-
 	objc_send_initialize((id)newSuper); // also initializes the metaclass
 	objc_update_dtable_for_new_superclass(cls->isa, newSuper->isa);
 	objc_update_dtable_for_new_superclass(cls, newSuper);