Optimistic Transactional Boosting

Abstract

The last two decades witnessed the success of many efficient designs of concurrent data structures. A large set of them has a common base principle: each operation is split into a read-only traversal phase, which scans the data structure without locking or monitoring, and a read-write commit phase, which atomically validates the output of the traversal phase and applies the needed modifications to the data structure. In this paper we introduce Optimistic Transactional Boosting (OTB), an optimistic methodology for extending those designs in order to support the composition of multiple operations into one atomic execution by building a single traversal phase and a single commit phase for the whole atomic execution. As a result, OTB-based data structures are optimistic and composable. The former because they defer any locking and/or monitoring to the commit phase of the entire atomic execution; the latter because they allow the execution of multiple operations atomically. Additionally, in this paper we provide a theoretical model for analyzing OTB-based data structures and proving their correctness. In particular, we extended a recent approach that models concurrent data structures by including the two notions of optimism and composition of operations.