An alternative to Quiescence: Tranquility

This paper revisits a problem that was identified by Kramer and Magee: placing a system in a consistent state before and after runtime changes (1990). We show that their notion of quiescence as a necessary and sufficient condition for safe runtime changes is too strict and violates the black-box design principle. We introduce a weaker condition, tranquility; easier to obtain, less disruptive for the system and still sufficient to ensure application consistency. We also present an implementation of this concept in a component middleware platform