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This paper revisits a problem that was identified by Kramer and Magee: placing a system in a consistent state before and after runtime changes [16]. 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.

This position paper describes ongoing work in which the Java-based SEESCOA component system is extended with functionality for run-time evolution. First, an assessment is made of the state-of-the-art in dynamic updating, and the applicability of existing systems for dynamic updating is examined. Then a new approach is presented, in which the concept of ports is used to redirect messages between components. The problem of class-file reloading in the JVM is avoided by modification of the classes at load-time to include version information. The predictability requirement of embedded systems is assured by updating all component instances at once.

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