Stable predicate detection in dynamic systems

Detection of stable predicates is fundamental to distributed application development and control. Stable predicates are distinguished by the fact that once they are true in some consistent global state, they remain true indefinitely. We present a protocol for the detection of stable predicates within dynamic systems (in which process membership may not be static). Unlike existing protocols, the presented protocol is not restricted to the detection of distributed termination and is based upon the use of approximately synchronized clocks. When clocks are approximately synchronized, the difference between the readings of any two clocks at an instant of time is kept within some known bound. Although clocks are assumed to be synchronized, temporary loss of synchronization is tolerated. The use of a global time base facilitates detection of predicates that remain true only after becoming true at some instant of time, while correctly detecting predicates that remain true upon becoming true in some consistent global state