Atomic snapshots in O(log³ n) steps using randomized helping

A randomized construction of unbounded snapshots objects from atomic registers is given. The cost of each snapshot operation is O(log3 n) atomic register steps with high probability, where n is the number of processes, even against an adaptive adversary. This is an exponential improvement on the linear cost of the previous best known unrestricted snapshot construction [7,8] and on the linear lower bound for deterministic constructions [9], and does not require limiting the number of updates as in previous sublinear constructions [4]. One of the main ingredients in the construction is a novel randomized helping technique that allows out-of-date processes to obtain up-to-date information without running into covering lower bounds.