AMECOS: A Modular Event-based Framework for Concurrent Object Specification

TL;DR

AMECOS is a modular, event-based framework for specifying distributed systems that enhances expressiveness and efficiency by focusing on interactions between concurrent objects, and it includes hierarchies of ordering semantics and an axiomatic proof of consensus impossibility.

Contribution

It introduces AMECOS, a novel modular framework for specifying distributed systems using concurrent object interactions, improving over traditional sequential specifications.

Findings

Successfully specified various concurrent objects like registers and consensus.

Developed hierarchies of ordering semantics for distributed systems.

Provided a new axiomatic proof of the impossibility of consensus.

Abstract

In this work, we introduce a modular framework for specifying distributed systems that we call AMECOS. Specifically, our framework departs from the traditional use of sequential specification, which presents limitations both on the specification expressiveness and implementation efficiency of inherently concurrent objects, as documented by Casta\~neda, Rajsbaum and Raynal in CACM 2023. Our framework focuses on the interactions between the various system components, specified as concurrent objects. Interactions are described with sequences of object events. This provides a modular way of specifying distributed systems and separates legality (object semantics) from other issues, such as consistency. We demonstrate the usability of our framework by (i) specifying various well-known concurrent objects, such as registers, shared memory, message-passing, reliable broadcast, and consensus, (ii) providing hierarchies of ordering semantics (namely, consistency hierarchy, memory hierarchy, and reliable broadcast hierarchy), and (iii) presenting a novel axiomatic proof of the impossibility of the well-known Consensus problem.