Alistarh, Dan; Kopinsky, Justin; Li, Jerry; Shavit, Nir N
High-performance concurrent priority queues are essential for applications such as task scheduling and discrete event simulation. Unfortunately, even the best performing implementations do not scale past a number of threads in the single digits. This is because of the sequential bottleneck in accessing the elements at the head of the queue in order to perform a DeleteMin operation. In this paper, we present the SprayList, a scalable priority queue with relaxed ordering semantics. Starting from a non-blocking SkipList, the main innovation behind our design is that the DeleteMin operations avoid a sequential bottleneck by "spraying" themselves onto the head of the SkipList list in a coordinated fashion. The spraying is implemented using a carefully designed random walk, so that DeleteMin returns an element among the first O(plog3p) in the list, with high probability, where p is the number of threads. We prove that the running time of a DeleteMin operation is O(log3p), with high probability, independent of the size of the list. Our experiments show that the relaxed semantics allow the data structure to scale for high thread counts, comparable to a classic unordered SkipList. Furthermore, we observe that, for reasonably parallel workloads, the scalability benefits of relaxation considerably outweigh the additional work due to out-of-order execution.
Support is gratefully acknowledged from the National Science Foundation under grants CCF-1217921, CCF-1301926, and IIS-1447786, the Department of Energy under grant ER26116/DE-SC0008923, and the Oracle and Intel corporations.
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PPoPP: Principles and Practice of Parallel Pogramming
Alistarh D, Kopinsky J, Li J, Shavit N. The SprayList: A scalable relaxed priority queue. In: Vol 2015-January. ACM; 2015:11-20. doi:10.1145/2688500.2688523
Alistarh, D., Kopinsky, J., Li, J., & Shavit, N. (2015). The SprayList: A scalable relaxed priority queue (Vol. 2015–January, pp. 11–20). Presented at the PPoPP: Principles and Practice of Parallel Pogramming, ACM. https://doi.org/10.1145/2688500.2688523
Alistarh, Dan, Justin Kopinsky, Jerry Li, and Nir Shavit. “The SprayList: A Scalable Relaxed Priority Queue,” 2015–January:11–20. ACM, 2015. https://doi.org/10.1145/2688500.2688523.
D. Alistarh, J. Kopinsky, J. Li, and N. Shavit, “The SprayList: A scalable relaxed priority queue,” presented at the PPoPP: Principles and Practice of Parallel Pogramming, 2015, vol. 2015–January, pp. 11–20.
Alistarh D, Kopinsky J, Li J, Shavit N. 2015. The SprayList: A scalable relaxed priority queue. PPoPP: Principles and Practice of Parallel Pogramming vol. 2015–January. 11–20.
Alistarh, Dan, et al. The SprayList: A Scalable Relaxed Priority Queue. Vol. 2015–January, ACM, 2015, pp. 11–20, doi:10.1145/2688500.2688523.