Read-Write Memory and k-Set Consensus as an Affine Task

TL;DR

This paper demonstrates that the read-write memory model with k-set consensus objects can be characterized as an affine task within the iterated immediate snapshot framework, providing a new combinatorial understanding of such models.

Contribution

It introduces a simple affine task representation for the model with k-set consensus objects, extending the affine task framework beyond traditional read-write memory models.

Findings

The read-write model with k-set consensus is captured by a subset of 2-round IS runs.

Affine tasks can represent models with additional abstractions like k-set consensus.

First combinatorial characterization of models with abstractions other than read-write memory.

Abstract

The wait-free read-write memory model has been characterized as an iterated \emph{Immediate Snapshot} (IS) task. The IS task is \emph{affine}---it can be defined as a (sub)set of simplices of the standard chromatic subdivision. It is known that the task of \emph{Weak Symmetry Breaking} (WSB) cannot be represented as an affine task. In this paper, we highlight the phenomenon of a "natural" model that can be captured by an iterated affine task and, thus, by a subset of runs of the iterated immediate snapshot model. We show that the read-write memory model in which, additionally, $k$-set-consensus objects can be used is, unlike WSB, "natural" by presenting the corresponding simple affine task captured by a subset of $2$-round IS runs. Our results imply the first combinatorial characterization of models equipped with abstractions other than read-write memory that applies to generic tasks.