This paper introduces ReDAC, a new algorithm for dynamic reconfiguration of multi-threaded applications. In order to achieve high reliability and availability, distributed component software has to support dynamic reconfiguration. Typical examples include the application of hot-fixes to deal with security vulnerabilities. ReDAC can be implemented on top of the modern component-platforms Java and .NET. We extend the statical term component, denoting a unit of deployment, to runtime by defining a capsule (runtime component instance) to be a set of interconnected objects. This allows us to apply dynamic updates at the level of components during runtime without stopping whole applications. Using system-wide unique identifiers for threads (logical thread IDs), we can detect and also bring capsules into a reconfigurable state by selectively blocking threads, relying on data structures maintained by additional logic integrated into the capsules using aspect-oriented programming. An important contribution of this paper is that ReDAC supports the dynamic reconfiguration of distributed multi-threaded and re-entrant components with cyclic call dependencies.
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