Low-disruptive dynamic updating of Java applications

ContextIn-use software systems are destined to change in order to fix bugs or add new features. Shutting down a running system before updating it is a normal practice, but the service unavailability can be annoying and sometimes unacceptable. Dynamic software updating (DSU) migrates a running software system to a new version without stopping it. State-of-the-art Java DSU systems are unsatisfactory as they may cause a non-negligible system pause during updating.ObjectiveIn this paper we present Javelus, a Java HotSpot VM-based Java DSU system with very short pausing time.MethodInstead of updating everything at once when the running application is suspended, Javelus only updates the changed code during the suspension, and migrates stale objects on-demand after the application is resumed. With a careful design this lazy approach neither sacrifices the update flexibility nor introduces unnecessary object validity checks or access indirections.ResultsEvaluation experiments show that Javelus can reduce the updating pausing time by one to two orders of magnitude without introducing observable overheads before and after the dynamic updating.ConclusionOur experience with Javelus indicates that low-disruptive and type-safe dynamic updating of Java applications can be practically achieved with a lazy updating approach.