A JVM-Managed Concurrent Unrolled List-Based Set Using Lazy Synchronization

Abstract: The multicore revolution of the early 21st century has introduced a multitude of multiprocessor synchronization techniques for designing concurrent data structures. This thesis explores the concept of “unrolling”, or storing multiple data items per node, in order to increase the concurrent throughput of linked-lists, or more specifically list-based sets of linked nodes. Our contribution is a concurrent unrolled list-based set implemented in the Java programming language which uses lock-based lazy synchronization with memory management handled by the Java Virtual Machine (JVM). Our unrolled list implementation provides decreased traversal overhead over the state-of-the-art concurrent linked lists under limited contention, along with improved spatial locality due to unrolled node data items being stored in sequential memory locations. Our results show that in comparison to the state-of-the- art lock-based and lock-free concurrent list-based set implementations in Java, our concurrent unrolled list-based set provides between 1.7x to 12.2x increased concurrent throughput under medium contention, and 25.7x to 196.5x increased concurrent throughput under low contention, depending on the ratio of write to read operations. Furthermore, we show that unrolling a concurrent linked-list can provide at least 60% of the performance of the Java concurrency package’s native lock-free skiplist, namely ConcurrentSkipListSet.