Mailbox Types for Unordered Interactions

TL;DR

This paper introduces a type system for networks of processes communicating via unordered mailboxes, ensuring protocol conformance, deadlock freedom, and junk freedom, applicable to various concurrency models.

Contribution

It presents a mailbox calculus extending the asynchronous π-calculus, enabling analysis of dynamic, heterogeneous process networks with a novel type system.

Findings

Processes are deadlock free and never fail due to unexpected messages.

The calculus can encode non-uniform concurrent objects and extended binary sessions.

The type system guarantees junk freedom for a significant class of processes.

Abstract

We propose a type system for reasoning on protocol conformance and deadlock freedom in networks of processes that communicate through unordered mailboxes. We model these networks in the mailbox calculus, a mild extension of the asynchronous {\pi}-calculus with first-class mailboxes and selective input. The calculus subsumes the actor model and allows us to analyze networks with dynamic topologies and varying number of processes possibly mixing different concurrency abstractions. Well-typed processes are deadlock free and never fail because of unexpected messages. For a non-trivial class of them, junk freedom is also guaranteed. We illustrate the expressiveness of the calculus and of the type system by encoding instances of non-uniform, concurrent objects, binary sessions extended with joins and forks, and some known actor benchmarks.