Abstract. Communication is becoming one of the central elements in software development. As a potential typed foundation for structured communication-based programming, session types have been studied over the last decade for a wide range of process calculi and programming languages, focussing on binary (twoparty) sessions. This work extends the foregoing theories of binary session types to multiparty, asynchronous sessions, which often arise in practical communicationcentred applications. Presented as a typed calculus for mobile processes, the theory introduces a new notion of types in which interactions involving multiple peers are directly abstracted as a global scenario. Global types retain a friendly type syntax of binary session types while capturing complex causal chains of multiparty asynchronous interactions. A global type plays the role of a shared agreement among communication peers, and is used as a basis of efficient type checking through its projection onto individual peers. The fundamental properties of the session type discipline such as communication safety and progress are

Abstract. This paper demonstrates the impact of integrating session types and object-oriented programming, through their implementation in Java. Session types provide high-level abstraction for structuring a series of interactions in a simple and concise syntax, and ensure type-safe communications between distributed peers. We present the first full implementation of a language and runtime for session-based distributed programming featuring asynchronous message passing, delegation and session subtyping, combined with class downloading and exceptions. The compilation and runtime framework of our language effectively maps session abstraction onto underlying transports and guarantees communication safety through static and dynamic session type checking. We have implemented two alternative protocols for performing correct and efficient session delegation and prove their correctness. Benchmark results show the session abstraction can be realised with minimal runtime overhead. 1

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. 1

We suggest an amalgamation of communication based programming (centred on sessions) and object oriented programming, whereby sessions between concurrent threads are amalgamated with methods. In our proposal threads consist of the execution of session bodies on objects and communicate with each other through asynchronously sending/receiving objects on channels. The choice on how to respond to a session request is based on the name of the request and the class of the object receiving the request, the choice on how to continue a session is made on the basis of the class of the object sent/received. Sessions can be delegated to other sessions, although session themselves are not first class objects. We demonstrate our ideas through a core language with generic types, SAM g, and an example. We then formalize a small calculus, Feather SAMg, and prove subject reduction and progress. The latter property is notoriously difficult to achieve in concurrent calculi.

Abstract. We suggest an amalgamation of the session type and the object oriented paradigm whereby sessions are amalgamated with methods; where threads consist of the execution of session bodies on objects and communicate with each other through asynchronously sending/receiving objects on channels; where the choice on how to respond to a session request is based on the name of the request and the class of the object receiving the request; where the choice on how to continue a session is made on the basis of the class of the object sent/received; and where sessions are not first class, but can be delegated to other sessions. We demonstrate our ideas through a small language, STOOP, and an example. We formalize a smaller calculus, Feather STOOP, and give a formal definition, and prove subject reduction and progress. The latter property is notoriously difficult and sometimes impossible to achieve in sessions languages, however it holds in Feather STOOP. 1

Communication is becoming one of the central elements in software development. As a potential typed foundation for structured communication-centred programming, session types have been studied over the last decade for a wide range of process calculi and programming languages, focussing on binary (two-party) sessions. This work extends the foregoing theories of binary session types to multiparty, asynchronous sessions, which often arise in practical communication-centred applications. Presented as a typed calculus for mobile processes, the theory introduces a new notion of types in which interactions involving multiple peers are directly abstracted as a global scenario. Global types retain a friendly type syntax of binary session types while capturing complex causal chains of multiparty asynchronous interactions. A global type plays the role of a shared agreement among communication peers, and is used as a basis of efficient type checking through its projection onto individual peers. The fundamental properties of the session type discipline such as communication safety, progress and session fidelity are established for general n-party asynchronous interactions.