Fast Implementations of Shared Objects using Fetch & Add

In this paper we present efficient implementations of shared objects from Fetch&Add registers. We present the first snapshot implementation which has time complexity O(1) for both scan and update. Using this implementation we can directly obtain an active set with constant time complexity for all three operations, join, leave and getSet. We also present the first universal construction which has time complexity O(1). This construction proves that a lower bound of Ω(log n) on the number of LL/SC registers required for implementing a universal object can be beaten if we employ a constant number of Fetch&Add registers (in addition to one LL/SC register). Our algorithms improve upon existing implementations of these objects and they have several interesting implications on the complexity of many known implementations of other shared objects that use any of the implemented objects as one of their components (i.e., existing partial snapshot algorithms and others). Despite these implications, they are themselves very simple and some of them are of practical interest in several cases.