I think you're confusing Macintosh apples with Apple Macintoshes. OO and threads have little to do with each-other. Sure, there should be an easy way of having objects be thread-safe, but that's not a matter for UNIVERSAL, which provides _methods_ that are inherited by all objects. Thread-saftey is going to be more a matter for attributes, and the implementation of attributes is sepperate from the implementation of methods, I belive.

As for tie and overloads, they're likely to be completly different in perl6, almost to the point of unrecognizablity.

As for locks, I don't think there's a clean way of doing that, quite simply, without real support for that in the implementing code. There isn't a magic way to say :lockable, because that means different things for different implementations.