A more Pragmatic Implementation of the Lock-free, Ordered, Linked List

TL;DR

This paper presents a practical enhancement to lock-free ordered linked lists by reducing retries after failed CAS operations through approximate backwards pointers, significantly improving performance across multiple hardware systems.

Contribution

It introduces a novel approach that minimizes full retries in lock-free lists by maintaining approximate backwards pointers, enhancing efficiency in concurrent environments.

Findings

Significant performance improvements observed in benchmarks.

Reduces retries in lock-free list operations.

Effective across diverse hardware architectures.

Abstract

The lock-free, ordered, linked list is an important, standard example of a concurrent data structure. An obvious, practical drawback of textbook implementations is that failed compare-and-swap (CAS) operations lead to retraversal of the entire list (retries), which is particularly harmful for such a linear-time data structure. We alleviate this drawback by first observing that failed CAS operations under some conditions do not require a full retry, and second by maintaining approximate backwards pointers that are used to find a closer starting position in the list for operation retry. Experiments with both a worst-case deterministic benchmark, and a standard, randomized, mixed-operation throughput benchmark on three shared-memory systems (Intel Xeon, AMD EPYC, SPARC-T5) show practical improvements ranging from significant, to dramatic, several orders of magnitude.