Alexander T. Garthwaite

\bf DCAS-Based Concurrent Deques

Abstract.The computer industry is currently examining the use of strong synchronization operations such as double compare-and-swap (DCAS) as a means of supporting non-blocking synchronization on future multiprocessor machines. However, before such a strong primitive will be incorporated into hardware design, its utility needs to be proven by developing a body of effective non-blocking data structures using DCAS.As part of this effort, we present two new linearizable non-blocking implementations of concurrent deques using the DCAS operation. The first uses an array representation, and improves on previous algorithms by allowing uninterrupted concurrent access to both ends of the deque while correctly handling the difficult boundary cases when the deque is empty or full. The second uses a linked-list representation, and is the first non-blocking, dynamically-sized deque implementation. It too allows uninterrupted concurrent access to both ends of the deque. We have proved these algorithms correct with the aid of a mechanical theorem prover; we describe these proofs in the paper.