The Prioritized and Distributed Synchronization in Distributed Groups

A simple and cheap algorithm is presented to allow prioritized mutual exclusion. There are several groups. All the members of a same group have the same level priority. Our algorithm is a token-based algorithm. Each group of participants (site) is represented by a tree structure. Inside a group, the requests are recorded in a global queue which circulates simultaneously and together with the token. The participant holding the token is the root of the tree linked to the router of the group. When a router transmits the token to another group, it preserves the role of the router in its group. The relation between routers is also represented by an rooted tree, the root is the router of the group holding the token. Besides a static logical structure similar to that used in Raymond's algorithm, our algorithm manages a global requester queue. If the requesting site and the owner of the token are in the same group, there is a reorganization of the group tree. If they are not in the same group, the tree of the requesting site and the tree of routers are reorganized. Algorithm in one group and extension to some groups are presented.