Generalised Multiparty Session Types with Crash-Stop Failures (Technical Report)

TL;DR

This paper extends multiparty session types to handle crash-stop failures, enabling verification of more realistic protocols where processes may crash, using minimal syntax changes and model checking for safety and liveness properties.

Contribution

It introduces a generalized MPST theory with crash-stop failures, allowing verification of protocols under crash scenarios with minimal syntax modifications.

Findings

Validates more protocols with crash failures.

Proves type safety and protocol conformance.

Uses model checking to verify properties in crash scenarios.

Abstract

Session types enable the specification and verification of communicating systems. However, their theory often assumes that processes never fail. To address this limitation, we present a generalised multiparty session type (MPST) theory with crash-stop failures, where processes can crash arbitrarily. Our new theory validates more protocols and processes w.r.t. previous work. We apply minimal syntactic changes to standard session {\pi}-calculus and types: we model crashes and their handling semantically, with a generalised MPST typing system parametric on a behavioural safety property. We cover the spectrum between fully reliable and fully unreliable sessions, via optional reliability assumptions, and prove type safety and protocol conformance in the presence of crash-stop failures. Introducing crash-stop failures has non-trivial consequences: writing correct processes that handle all crash scenarios can be difficult. Yet, our generalised MPST theory allows us to tame this complexity, via model checking, to validate whether a multiparty session satisfies desired behavioural properties, e.g. deadlock-freedom or liveness, even in presence of crashes. We implement our approach using the mCRL2 model checker, and evaluate it with examples extended from the literature.