The levelarray: A fast, practical long-lived renaming algorithm

Dan Alistarh, Justin Kopinsky, Alexander Matveev, Nir Shavit

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review


The long-lived renaming problem appears in shared-memory systems where a set of threads need to register and deregister frequently from the computation, while concurrent operations scan the set of currently registered threads. Instances of this problem show up in concurrent implementations of transactional memory, flat combining, thread barriers, and memory reclamation schemes for lock-free data structures. In this paper, we analyze a randomized solution for long-lived renaming. The algorithmic technique we consider, called the Level Array, has previously been used for hashing and one-shot (single-use) renaming. Our main contribution is to prove that, in long-lived executions, where processes may register and deregister polynomially many times, the technique guarantees constant steps on average and O (log log n) steps with high probability for registering, unit cost for deregistering, and O (n) steps for collect queries, where n is an upper bound on the number of processes that may be active at any point in time. We also show that the algorithm has the surprising property that it is self-healing: under reasonable assumptions on the schedule, operations running while the data structure is in a degraded state implicitly help the data structure re-balance itself. This subtle mechanism obviates the need for expensive periodic rebuilding procedures. Our benchmarks validate this approach, showing that, for typical use parameters, the average number of steps a process takes to register is less than two and the worst-case number of steps is bounded by six, even in executions with billions of operations. We contrast this with other randomized implementations, whose worst-case behavior we show to be unreliable, and with deterministic implementations, whose cost is linear in n.

Original languageEnglish
Title of host publicationProceedings - International Conference on Distributed Computing Systems
PublisherInstitute of Electrical and Electronics Engineers Inc.
Number of pages10
ISBN (Electronic)9781479951680
StatePublished - 29 Aug 2014
Event2014 IEEE 34th International Conference on Distributed Computing Systems, ICDCS 2014 - Madrid, Spain
Duration: 30 Jun 20143 Jul 2014

Publication series

NameProceedings - International Conference on Distributed Computing Systems


Conference2014 IEEE 34th International Conference on Distributed Computing Systems, ICDCS 2014


  • long-lived data structures
  • randomized algorithms
  • renaming
  • shared memory


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