Chapter 5 Fast and Lock - Free Concurrent Priority Queues for Multi - Thread Systems 1

We present an efficient and practical lock-free implementation of a concurrent priority queue that is suitable for both fully concurrent (large multiprocessor) systems as well as pre-emptive (multi-process) systems. Many algorithms for concurrent priority queues are based on mutual exclusion. However, mutual exclusion causes blocking which has several drawbacks and degrades the system’s overall performance. Non-blocking algorithms avoid blocking, and several implementations have been proposed. Previously known non-blocking algorithms of priority queues did not perform well in practice This is an extended and revised version of the paper with the same title that was presented at IPDPS 2003 [24] that was awarded with the best paper award in the algorithms category, and published as a technical report [25]. 2 CHAPTER 5. LOCK-FREE PRIORITY QUEUE because of their complexity, and they are often based on non-available atomic synchronization primitives. Our algorithm is based on the randomized sequential list structure called skip list, and a real-time extension of our algorithm is also described. In our performance evaluation we compare our algorithm with a well representable set of earlier implementations of priority queues known. The experimental results clearly show that our lock-free implementation outperforms the other lock-based implementations in practical scenarios for 3 threads and more, both on fully concurrent as well as on pre-emptive systems.