Abstract The Weakest Failure Detectors to Boost Obstruction-Freedom ∗

This paper determines necessary and sufficient conditions to implement wait-free and non-blocking contention managers in a shared memory system. The necessary conditions hold even when universal objects (like compare-and-swap) or random oracles are available, whereas the sufficient ones assume only registers. We show that failure detector ♦P is the weakest to convert any obstruction-free algorithm into a wait-free one, and Ω ∗ , a new failure detector which we introduce in this paper, and which is strictly weaker than ♦P but strictly stronger than Ω, is the weakest to convert any obstruction-free algorithm into a non-blocking one.