Abstract

This paper introduces ReDAC, a new algorithm for dynamic reconfiguration of multi-threaded applications with cyclic dependencies. 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 applications with cyclic call graphs.

Virtual machine-based programming languages, such as Java and C # have made the programming of desktop computer systems simpler, less error-prone and more efficient. Embedded systems development rarely benefits from this advantages. This is because the disciplines special needs, such as direct hardware access and timelininess, are rarely considered in in these environments. In particular, virtual machines usually do not allow for accessing hardware directly, making it impossible to express substantial parts of embedded systems inside the virtual environment. By specifying additional rules, describing an implementation of a conforming compiler, and presenting examples, we show how the virtual machine defined by the ECMA standard 335 can be carefully extended to support hardware-near programming.