On the Importance of Registers for Computability

  • Rati Gelashvili
  • Mohsen Ghaffari
  • Jerry Li
  • Nir Shavit
Part of the Lecture Notes in Computer Science book series (LNCS, volume 8878)


All consensus hierarchies in the literature assume that we have, in addition to copies of a given object, an unbounded number of registers. But why do we really need these registers?

This paper considers what would happen if one attempts to solve consensus using various objects but without any registers. We show that under a reasonable assumption, objects like queues and stacks cannot emulate the missing registers. We also show that, perhaps surprisingly, initialization, shown to have no computational consequences when registers are readily available, is crucial in determining the synchronization power of objects when no registers are allowed. Finally, we show that without registers, the number of available objects affects the level of consensus that can be solved.

Our work thus raises the question of whether consensus hierarchies which assume an unbounded number of registers truly capture synchronization power, and begins a line of research aimed at better understanding the interaction between read-write memory and the powerful synchronization operations available on modern architectures.


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  1. 1.
    Afek, Y., Gafni, E., Tromp, J., Vitányi, P.M.B.: Wait-free test-and-set. In: Segall, A., Zaks, S. (eds.) WDAG 1992. LNCS, vol. 647, pp. 85–94. Springer, Heidelberg (1992)CrossRefGoogle Scholar
  2. 2.
    Alistarh, D., Attiya, H., Gilbert, S., Giurgiu, A., Guerraoui, R.: Fast Randomized Test-and-Set and Renaming. In: Lynch, N.A., Shvartsman, A.A. (eds.) DISC 2010. LNCS, vol. 6343, pp. 94–108. Springer, Heidelberg (2010)CrossRefGoogle Scholar
  3. 3.
    Attiya, H., Bar-Noy, A., Dolev, D., Peleg, D., Reischuk, R.: Renaming in an asynchronous environment. Journal of the ACM (JACM) 37(3), 524–548 (1990)CrossRefzbMATHMathSciNetGoogle Scholar
  4. 4.
    Bazzi, R.A., Neiger, G., Peterson, G.L.: On the use of registers in achieving wait-free consensus. Distributed Computing 10(3), 117–127 (1997)CrossRefGoogle Scholar
  5. 5.
    Borowsky, E., Gafni, E., Afek, Y.: Consensus power makes (some) sense! In: Proceedings of the Thirteenth Annual ACM Symposium on Principles of Distributed Computing, pp. 363–372. ACM (1994)Google Scholar
  6. 6.
    Gafni, E., Merritt, M., Taubenfeld, G.: The concurrency hierarchy, and algorithms for unbounded concurrency. In: Proceedings of the Twentieth Annual ACM Symposium on Principles of Distributed Computing, pp. 161–169. ACM (2001)Google Scholar
  7. 7.
    Herlihy, M.: Wait-free synchronization. ACM Transactions on Programming Languages and Systems (TOPLAS) 13(1), 124–149 (1991)CrossRefGoogle Scholar
  8. 8.
    Herlihy, M.P., Wing, J.M.: Linearizability: A correctness condition for concurrent objects. ACM Transactions on Programming Languages and Systems (TOPLAS) 12(3), 463–492 (1990)CrossRefGoogle Scholar
  9. 9.
    Jayanti, P.: Robust wait-free hierarchies. Journal of the ACM (JACM) 44(4), 592–614 (1997)CrossRefzbMATHMathSciNetGoogle Scholar
  10. 10.
    Merritt, M., Taubenfeld, G.: Computing with infinitely many processes. In: Herlihy, M.P. (ed.) DISC 2000. LNCS, vol. 1914, pp. 164–178. Springer, Heidelberg (2000)CrossRefGoogle Scholar
  11. 11.
    Moir, M., Anderson, J.H.: Fast, long-lived renaming (Extended abstract). In: Tel, G., Vitányi, P. (eds.) WDAG 1994. LNCS, vol. 857, pp. 141–155. Springer, Heidelberg (1994)CrossRefGoogle Scholar

Copyright information

© Springer International Publishing Switzerland 2014

Authors and Affiliations

  • Rati Gelashvili
    • 1
  • Mohsen Ghaffari
    • 1
  • Jerry Li
    • 1
  • Nir Shavit
    • 1
  1. 1.Massachusetts Institute of TechnologyCambridgeUSA

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