Fair Synchronization in the Presence of Process Crashes and its Weakest Failure Detector

A non-blocking implementation of a concurrent object is an implementation that does not prevent concurrent accesses to the internal representation of the object, while guaranteeing the deadlock-freedom progress condition without using locks. Considering a failure free context, G. Taubenfeld has introduced (DISC 2013) a simple modular approach, captured under a new problem called the it fair synchronization problem, to transform a non-blocking implementation into a starvation-free implementation satisfying a strong fairness requirement. This paper extends this approach in several directions. It first generalizes the fair synchronization problem to read/write asynchronous systems where any number of processes may crash. Then, it introduces a new failure detector and uses it to solve the fair synchronization problem when processes may crash. This failure detector, denoted QP (Quasi Perfect), is very close to, but strictly weaker than, the perfect failure detector. Last but not least, the paper shows that the proposed failure detector QP is optimal in the sense that the information on failures it provides to the processes can be extracted from any algorithm solving the fair synchronization problem in the presence of any number of process crash failures.