Software variability mechanisms for improving run-time performance

A variability mechanism is a software implementation technique that realizes a choice in the features that are incorporated into a software system. Variability mechanisms are essential for the implementation of configurable software, but the nature of mechanisms as structuring abstractions is not well understood. Mechanisms are often equated with their stereotypical realizations. As a consequence, certain variability mechanisms are generally viewed as having limited applicability due to run-time performance overhead. We claim that it is feasible and useful to realize variability mechanisms in novel ways to improve the run-time performance of software systems. This claim is supported by the implementation and evaluation of three examples. The first is the flexible generation of performance-optimized code from high-level specifications. As exemplified by Flick, an interface definition language (IDL) compiler kit, concepts from traditional programming language compilers can be applied to bring both flexibility and optimization to the domain of IDL compilation. The second is a method for realizing design patterns within software that is neither object-oriented nor, for the most part, dynamically configured. By separating static software design from dynamic system behavior, this technique enables more effective and domain-specific detection of design errors, prediction of run-time behavior, and more effective optimization. The method is demonstrated using a suite of operating-system components. The third, middleware-based brokering of resources, can improve the ability of multi-agent, real-time applications to maintain quality of service (QoS) in the face of resource contention. A CPU broker, for instance, may use application feedback and other inputs to adjust CPU allocations at run time. This helps to ensure that applications continue to function, or at least degrade gracefully, under load.