ABSTRACT:

First class messages, which we call message continuations, 
provide object-oriented concurrent programming languages with 
extensibility in modeling and programming communication schemes 
such as asynchronous communication, multicasting, sophisticated 
synchronization constraints, inter-object synchronization, 
concurrency control, resource management, and so on. In spite of 
its powerful extensibility, the framework is sound in that the 
framework guarantees that no program can destroy the semantics of 
the built-in communication primitives. This good property was 
obtained by categorization of message continuations and careful 
design of the primitive operations on message continuations.