Characterizing and detecting the set of global states seen by all observers of a distributed computation

A consistent observation of a given distributed computation is a sequence of global states that could be produced by executing that computation on a monoprocessor system. Therefore a distributed execution generally accepts several consistent observations. This paper concentrates on what all these observations have in common. An abstraction called common global state is defined. A necessary and sufficient condition characterizing such states is given. A monitor-based algorithm that detects them is also presented and proved correct. Previous works on detection of unstable properties of distributed computations are revisited and explained with this abstraction. Moreover other uses of such particular states are sketched.