Self-Stabilization in Spite of Distributed Control

Abstract

A systematic way for finding the algorithm ensuring some desired form of co-operation between a set of loosely coupled sequential processes can in general terms be described as follows: the relation “the system is in a legitimate state” is kept invariant. As a consequence, each intended individual process step that could possibly cause violation of that invariant relation has to be preceded by a test that it won’t do so, and depending on the outcome of that test the critical process step is either caused to take place or it —and with it the process of which it is a part— is delayed until a more favourable system state has been reached. With a suitable choice of the set of legitimate states one can indeed introduce the rule that a critical process step will be delayed only as long as its execution would lead to violation of the corresponding invariant relation.