Read-Modify-Writable Snapshots from Read/Write operations

TL;DR

This paper investigates the possibility of implementing Read-Modify-Writable snapshots using only basic read/write operations in concurrent shared-memory systems, presenting two novel algorithms under different process models.

Contribution

It introduces the first read/write RMWable snapshot algorithms for both finite and infinite process models, expanding understanding of what can be achieved with weaker synchronization primitives.

Findings

First read/write RMWable snapshot algorithms for finite processes.

First such algorithms for unbounded concurrency models.

Demonstrates feasibility of complex snapshots with minimal synchronization.

Abstract

In the context of asynchronous concurrent shared-memory systems, a snapshot algorithm allows failure-prone processes to concurrently and atomically write on the entries of a shared array MEM , and also atomically read the whole array. Recently, Read-Modify-Writable (RMWable) snapshot was proposed, a variant of snapshot that allows processes to perform operations more complex than just read and write, specifically, each entry MEM[k] is an arbitrary readable object. The known RMWable snapshot algorithms heavily rely on powerful low-level operations such as compare&swap or load-link/store-conditional to correctly produce snapshots of MEM. Following the large body of research devoted to understand the limits of what can be solved using the simple read/write low-level operations, which are known to be strictly weaker than compare&swap and load-link/store-conditional, we explore if RMWable snapshots are possible using only read/write operations. We present two read/write RMWable snapshot algorithms, the first one in the standard concurrent shared-memory model where the number of processes n is finite and known in advance, and the second one in a variant of the standard model with unbounded concurrency, where there are infinitely many processes, but at any moment only finitely many processes participate in an execution.