Fast and Fair Randomized Wait-Free Locks

BSTRACTWe present a randomized approach for wait-free locks with strong bounds on time and fairness in a context in which any process can be arbitrarily delayed. Our approach supports a tryLock operation that is given a set of locks, and code to run when all the locks are acquired. A tryLock operation, or attempt, may fail if there is contention on the locks, in which case the code is not run. Given an upper bound k known to the algorithm on the point contention of any lock, and an upper bound L on the number of locks in a try- Lock's set, a tryLock will succeed in acquiring its locks and running the code with probability at least 1/(kL). It is thus fair. Furthermore, if the maximum step complexity for the code in any lock is T , the attempt will take O(k2L2T ) steps, regardless of whether it succeeds or fails. The attempts are independent, thus if the tryLock is repeatedly retried on failure, it will succeed in O(k3L3T ) expected steps, and with high probability in not much more.