Concurrent Robin Hood Hashing

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. ACM Subject Classification Theory of computation → Concurrent algorithmsKeywords and phrases concurrency, Robin Hood Hashing, data-structures, hash tables, nonblocking Funding Funded by the Government of Ireland Postgraduate Scholarship.Acknowledgements I want to thank William Leiserson for his invaluable help with reviewing and feedback. I also want to thank Nir Shavit for extensive access to hardware for running the benchmarks.