Type-Safe Eventful Sessions in Java

Abstract

Abstract. Event-driven programming is a major paradigm in concurrent and communication-based programming, and a widely adopted approach to building scalable high-concurrency servers. However, traditional event-driven programs are more difficult to read, write and verify than their multi-threaded counterparts due to low-level APIs and fragmentation of control flow across disjoint event handlers. This paper presents a Java language extension and a novel type discipline for type-safe event-driven session programming that counters the problems of traditional event-based programming with abstractions and safety guarantees based on session types, while retaining the expressiveness and performance characteristics of events. The type discipline extends session types and their primitives with asynchronous input, session typecase and session set types, ensuring eventhandling safety and event progress in addition to the standard type soundness and communication safety. The advantages, expressiveness and performance of event-driven session programming are demonstrated through a range of examples and benchmarks, including a session-typed SMTP server.

On Asynchronous Session Semantics

“…We often omit ∆ if it is clear from the context. The typing system is similar with [2,13], and can be found in online Appendix [23]. We say that ∆ well configured if s : S ∈ ∆ , then s : S ∈ ∆ .…”

“…As will be discussed later, determinacy plays an essential role in our proofs while sequentiality is for simplicity of the mapping. We use the standard "select" primitive represented as a process, called selector [13]. It stores a collection of session channels, with each channel associated with an environment, binding variables to values.…”

“…Our translation is given formally, is type-preserving and is backed up by a rigorous semantic justification. While we do not detail in the main sections, the transform is implemented in the session-extension of Java [13,14], resulting in competitive performance in comparison with more ad-hoc transformations.…”

“…Asynchronous event-handling [13] introduces further subtleties in observational laws. Asynchronous event-based programming is characterised by reactive flows driven by the detection of events, that is message arrivals at local buffers.…”

Multiparty Session C: Safe Parallel Programming with Message Optimisation

“…Our previous work [29] applied Session Java (SJ) [19,20], Java enhanced with session types, to parallel algorithms. SJ treats only binary session types [17] and cannot guarantee deadlock freedom and global progress between more than two processes.…”