We present a wait-free algorithm for proper coloring the 𝑛 nodes of the asynchronous cycle 𝐶 𝑛 , where each crash-prone node starts with its (unique) identifier as input. The algorithm is independent of 𝑛 ⩾ 3, and runs in O(log * 𝑛) rounds in 𝐶 𝑛 . This round-complexity is optimal thanks to a known matching lower bound, which applies even to synchronous (failure-free) executions. The range of colors used by our algorithm, namely { 0, . . . , 4 }, is optimal too, thanks to a known lower bound on the minimum number of names for which renaming is solvable wait-free in shared-memory systems, whenever 𝑛 is a power of a prime. Indeed, our model coincides with the shared-memory model whenever 𝑛 = 3, and the minimum number of names for which renaming is possible in 3-process shared-memory systems is 5.
ACM Subject ClassificationTheory of computation → Distributed algorithms; Mathematics of computing → Graph coloring; Computer systems organization → Dependable and fault-tolerant systems and networks; Theory of computation → Models of computation Keywords and phrases graph coloring, LOCAL model, shared-memory model, immediate snapshot, renaming, wait-free algorithms.