Fair Termination of Multiparty Sessions

TL;DR

This paper introduces a novel type system that guarantees fair termination for complex multiparty sessions, including those with dependent participant choices, under realistic fairness assumptions, ensuring progress and compositional safety.

Contribution

It presents the first type system that ensures fair termination of multiparty sessions with dependencies, extending progress guarantees to more complex session interactions.

Findings

Guarantees fair termination under realistic fairness assumptions.

Ensures progress and safety in multiparty sessions with dependencies.

Enables compositional static analysis of session-based programs.

Abstract

There exists a broad family of multiparty sessions in which the progress of one session participant is not unconditional, but depends on the choices performed by other participants. These sessions fall outside the scope of currently available session type systems that guarantee progress. In this work we propose the first type system ensuring that well-typed multiparty sessions, including those exhibiting the aforementioned dependencies, fairly terminate. Fair termination is termination under a fairness assumption that disregards those interactions deemed unfair and therefore unrealistic. Fair termination, combined with the usual safety properties ensured within sessions, not only is desirable per se, but it entails progress and enables a compositional form of static analysis such that the well-typed composition of fairly terminating sessions results in a fairly terminating program.