self in that context would be the class. The issue he was facing is that in subclasses, "self", would refer to a different class and therefore the lock wouldn't

self in that context would be the class. The issue he was facing is that in subclasses, "self", would refer to a different class and therefore the lock wouldn't apply. What he's pointing out is that he resolved that issue by specifying the superclass explicitly. Personally, if I had to ensure synchronous calls to a class variable, I'd prefer to just restrict calls like this to a specific queue using dispatch_sync().