Controlled, systematic, and efficient code replacement for running Java programs

Abstract

We present a system that performs reversible and systematic changes to running Java applications without requiring them to be shutdown. PROSE is motivated by scenarios such as hotfixes, online program instrumentation and debugging, and evolution of critical legacy applications. Modifications take the form of replacement method bodies, and can use both type-based and regular expression patterns to select code for replacement. New code can make use of replaced method implementations cleanly, facilitating code evolution. Changes are composable, and may be reordered or selectively withdrawn at any time. Furthermore, the modifications are expressed as Java classes, providing additional development benefits. We describe the architecture of PROSE, the challenges of using aggressive inlining to achieve performance, and use standard benchmarks to demonstrate code performance comparable (or better than) compile-time systems from the Aspect-Oriented Programming community.