Concurrent tries with efficient non-blocking snapshots

Abstract

We describe a non-blocking concurrent hash trie based on shared-memory single-word compare-and-swap instructions. The hash trie supports standard mutable lock-free operations such as insertion, removal, lookup and their conditional variants. To ensure space-efficiency, removal operations compress the trie when necessary. We show how to implement an efficient lock-free snapshot operation for concurrent hash tries. The snapshot operation uses a single-word compare-and-swap and avoids copying the data structure eagerly. Snapshots are used to implement consistent iterators and a linearizable size retrieval. We compare concurrent hash trie performance with other concurrent data structures and evaluate the performance of the snapshot operation.