Hemlock : Compact and Scalable Mutual Exclusion

TL;DR

Hemlock is a new, highly efficient mutual exclusion lock that is compact, scalable, FIFO, and offers high throughput and low latency, outperforming existing spin locks in many scenarios.

Contribution

Hemlock introduces a simple, context-free, FIFO mutual exclusion lock that is both compact and scalable, with superior performance characteristics.

Findings

Competitive performance with best scalable spin locks

High throughput under contention

Low latency in uncontended cases

Abstract

We present Hemlock, a novel mutual exclusion locking algorithm that is extremely compact, requiring just one word per thread plus one word per lock, but which still provides local spinning in most circumstances, high throughput under contention, and low latency in the uncontended case. Hemlock is context-free -- not requiring any information to be passed from a lock operation to the corresponding unlock -- and FIFO. The performance of Hemlock is competitive with and often better than the best scalable spin locks.