wCQ: A Fast Wait-Free Queue with Bounded Memory Usage

TL;DR

wCQ is a novel wait-free concurrent queue that combines high performance with bounded memory usage, improving over existing lock-free and wait-free designs by ensuring wait-freedom and efficiency.

Contribution

The paper introduces wCQ, a wait-free queue that achieves both bounded memory and high performance, based on a variation of the SCQ design and fast-path-slow-path methodology.

Findings

wCQ demonstrates competitive performance on x86 and PowerPC architectures.

wCQ maintains bounded memory usage while providing wait-freedom.

Experimental results show wCQ outperforms or matches existing queues in speed and memory efficiency.

Abstract

The concurrency literature presents a number of approaches for building non-blocking, FIFO, multiple-producer and multiple-consumer (MPMC) queues. However, only a fraction of them have high performance. In addition, many queue designs, such as LCRQ, trade memory usage for better performance. The recently proposed SCQ design achieves both memory efficiency as well as excellent performance. Unfortunately, both LCRQ and SCQ are only lock-free. On the other hand, existing wait-free queues are either not very performant or suffer from potentially unbounded memory usage. Strictly described, the latter queues, such as Yang & Mellor-Crummey's (YMC) queue, forfeit wait-freedom as they are blocking when memory is exhausted. We present a wait-free queue, called wCQ. wCQ is based on SCQ and uses its own variation of fast-path-slow-path methodology to attain wait-freedom and bound memory usage. Our experimental studies on x86 and PowerPC architectures validate wCQ's great performance and memory efficiency. They also show that wCQ's performance is often on par with the best known concurrent queue designs.