Asynchronous Session Types and Progress for Object-Oriented Languages

Abstract. A session type is an abstraction of a sequence of heterogeneous values sent over one channel between two communicating processes. Session types have been introduced to guarantee consistency of the exchanged data and, more recently, progress of the session, i.e., the property that once a communication has been established, well-formed programs will never starve at communication points. A relevant feature which influences progress is whether the communication is synchronous or asynchronous. In this paper, we first formulate a typed asynchronous multi-threaded object-oriented language with thread spawning, iterative and higher order sessions. Then we study its progress through a new effect system. As far as we know, ours is the first session type system which assures progress in asynchronous communication.