If you tag objects as being either "owned" by a thread or "shared" then you could (in the python implementation) do something like: if (obj.owner == current_

If you tag objects as being either "owned" by a thread or "shared" then you could (in the python implementation) do something like: if (obj.owner == current_thread): # just get in and mess with it elsif (obj.owner == shared): # get in and mess with it under a lock else throw "not your obj - make this obj shared if you need that" From a language perspective, you'd just need a way to declare that an object was 'shared'. All other objs would be owned by their creating thread.