Stateful Behavioral Types for ABS

TL;DR

This paper introduces a novel specification language and type system for modeling and verifying complex multiparty protocols involving asynchronous interactions and heap side-effects in object-oriented actors.

Contribution

It presents a formal specification language with a behavioral type system for specifying and checking multiparty asynchronous protocols in actor-based systems.

Findings

Formalizes protocols as global types with first-order logic

Provides a model-theoretic semantics for types

Proves protocol adherence for well-typed programs

Abstract

It is notoriously hard to correctly implement a multiparty protocol which involves asynchronous/concurrent interactions and the constraints on states of multiple participants. To assist developers in implementing such protocols, we propose a novel specification language to specify interactions within multiple object-oriented actors and the side-effects on heap memory of those actors; a behavioral-type-based analysis is presented for type checking. Our specification language formalizes a protocol as a global type, which describes the procedure of asynchronous method calls, the usage of futures, and the heap side-effects with a first-order logic. To characterize runs of instances of types, we give a model-theoretic semantics for types and translate them into logical constraints over traces. We prove protocol adherence: If a program is well-typed w.r.t. a protocol, then every trace of the program adheres to the protocol, i.e., every trace is a model for the formula of its type.