# Causal Consistency for Reversible Multiparty Protocols

## TL;DR

This paper extends reversible semantics to multiparty communication protocols with asynchronous features, ensuring causal consistency and supporting complex rollback mechanisms in process languages.

## Contribution

It introduces a reversible semantics for multiparty protocols with asynchronous communication, expanding prior binary-focused work and proving causal consistency.

## Key findings

- Reversible semantics for multiparty protocols with asynchronous communication.
- Causal consistency of the proposed reversible semantics.
- Characterization of decoupled rollbacks with atomic semantics.

## Abstract

In programming models with a reversible semantics, computational steps can be undone. This paper addresses the integration of reversible semantics into process languages for communication-centric systems equipped with behavioral types. In prior work, we introduced a monitors-as-memories approach to seamlessly integrate reversible semantics into a process model in which concurrency is governed by session types (a class of behavioral types), covering binary (two-party) protocols with synchronous communication. The applicability and expressiveness of the binary setting, however, is limited. Here we extend our approach, and use it to define reversible semantics for an expressive process model that accounts for multiparty (n-party) protocols, asynchronous communication, decoupled rollbacks, and abstraction passing. As main result, we prove that our reversible semantics for multiparty protocols is causally-consistent. A key technical ingredient in our developments is an alternative reversible semantics with atomic rollbacks, which is conceptually simple and is shown to characterize decoupled rollbacks.