Deadlock-free Context-free Session Types

TL;DR

This paper introduces a novel type system for concurrent functional programs that uses context-free session types to ensure protocol adherence and deadlock freedom, even in complex cyclic communication topologies.

Contribution

It extends deadlock-free session types to a more expressive setting with context-free types, enabling verification of complex recursive and cyclic communication structures.

Findings

Proposes a new type system based on context-free session types.

Extends priority-based deadlock freedom to this expressive setting.

Proves well-typed programs respect protocols and are deadlock-free.

Abstract

We tackle the problem of statically ensuring that message-passing programs never run into deadlocks. We focus on concurrent functional programs governed by context-free session types, which can express rich tree-like structures not expressible in standard session types. We propose a new type system based on context-free session types: it enforces both protocol conformance and deadlock freedom, also for programs implementing cyclic communication topologies with recursion and polymorphism. We show how the priority-based approach to deadlock freedom can be extended to this expressive setting. We prove that well-typed concurrent programs respect their protocols and never deadlock.