The buck stops here: Order, chance, and coordination in distributed control

Distributed control for enforcing a global invariant can be achieved based on calculating the knowledge of processes. When the local knowledge of individual processes is insufficient, processes can temporarily join their knowledge by means of synchronization. While synchronization can be used to guarantee progress, it is computationally expensive and should be used sparsely. In this paper, we introduce several solutions for minimizing the synchronization overhead. One possibility is to calculate the knowledge of a process of whether or not the system can progress without it. This knowledge can be used by the process to avoid unnecessary synchronization. Because of the distributed nature of the system, mutual passing of responsibility, based on such knowledge may result in deadlocks. We discuss three independent solutions to this problem. Our first solution breaks the symmetry between processes in order to avoid such situations, while our second solution is based on chance (coin tossing). Finally, we use automatically constructed stable properties to increase the joint knowledge of processes in order to minimize the number of processes that need to interact.