Sigma: a fault-tolerant mutual exclusion algorithm in dynamic distributed systems subject to process crashes and memory losses

This paper introduces the Sigma algorithm that solves fault-tolerant mutual exclusion problem in dynamic systems where the set of processes may be large and change dynamically, processes may crash, and the recovery or replacement of crashed processes may lose all state information (memory losses). Sigma algorithm includes new messaging mechanisms to tolerate process crashes and memory losses. It does not require any extra cost for process recovery. The paper also shows that the threshold used by the Sigma algorithm is necessary for systems with process crashes and memory losses.