Understanding Read-Write Wait-Free Coverings in the Fully-Anonymous Shared-Memory Model

TL;DR

This paper explores the challenges of processor anonymity in shared-memory systems, proposing new concepts like group solvability and analyzing stable configurations to enable fundamental tasks such as snapshot, renaming, and consensus.

Contribution

It introduces the notion of group solvability for anonymous tasks and characterizes stable configurations, leading to wait-free solutions for snapshot, renaming, and consensus in anonymous models.

Findings

Stable configurations are characterized for anonymous read-write systems.

A wait-free snapshot algorithm is developed for fully-anonymous models.

Solutions for renaming and obstruction-free consensus are achieved in the anonymous setting.

Abstract

In the fully-anonymous (shared-memory) model, inspired by a biological setting, processors have no identifiers and memory locations are anonymous. This means that there is no pre-existing agreement among processors on any naming of the memory locations. In this work, we ask fundamental questions about the fully-anonymous model in the hope to obtain a better understanding of the role of naming and anonymity in distributed computing. First, we ask what it means to solve a task under processor anonymity. With tasks such as renaming, the traditional notion obviously does not apply. Instead of restricting ourselves to colorless tasks, we propose using the notion of group solvability, which allows transferring any task to processor-anonymous models. Second, the difficulty with anonymity is that processors can hardly avoid covering and then overwriting each other's writes, erasing information written by their predecessors. To get to the bottom of this phenomenon, we ask what system configurations are stable when processors keep reading and writing ad infinitum. Resolving this question leads us to a wait-free solution to the snapshot task, which then allows us to solve renaming and obstruction-free consensus.