Concurrent Robin Hood Hashing

TL;DR

This paper introduces a non-blocking, concurrent Robin Hood hash table algorithm that is portable, maintains low probe lengths, and outperforms other lock-free and transactional variants in various scenarios.

Contribution

It presents a novel obstruction-free K-CAS Robin Hood hash table algorithm requiring only single-word CAS, enhancing portability and performance.

Findings

Outperforms other lock-free algorithms in benchmarks

Maintains low probe length under high load

Operates efficiently with a single-word compare-and-swap

Abstract

In this paper we examine the issues involved in adding concurrency to the Robin Hood hash table algorithm. We present a non-blocking obstruction-free K-CAS Robin Hood algorithm which requires only a single word compare-and-swap primitive, thus making it highly portable. The implementation maintains the attractive properties of the original Robin Hood structure, such as a low expected probe length, capability to operate effectively under a high load factor and good cache locality, all of which are essential for high performance on modern computer architectures. We compare our data-structures to various other lock-free and concurrent algorithms, as well as a simple hardware transactional variant, and show that our implementation performs better across a number of contexts.