An optimistic approach to lock-free FIFO queues

First-in-first-out (FIFO) queues are among the most fundamental and highly studied concurrent data structures. The most effective and practical dynamic-memory concurrent queue implementation in the literature is the lock-free FIFO queue algorithm of Michael and Scott, included in the standard Java ^TM Concurrency Package. This work presents a new dynamic-memory concurrent lock-free FIFO queue algorithm that in a variety of circumstances performs better than the Michael and Scott queue. The key idea behind our new algorithm is a novel way of replacing the singly-linked list of Michael and Scott, whose pointers are inserted using a costly compare-and-swap (CAS) operation, by an “optimistic” doubly - linked list whose pointers are updated using a simple store, yet can be “fixed” if a bad ordering of events causes them to be inconsistent. We believe it is the first example of such an “optimistic” approach being applied to a real world data structure. A preliminary version of this paper appeared in the proceedings of the 18th International Conference on Distributed Computing (DISC) 2004, pages 117–131.