Incinerator -- Eliminating Stale References in Dynamic OSGi Applications

Java class loaders are commonly used in application servers to load, unload and update a set of classes as a unit. However, unloading or updating a class loader can introduce stale references to the objects of the outdated class loader. A stale reference leads to a memory leak and, for an update, to an inconsistency between the outdated classes and their replacements. To detect and eliminate stale references, we propose Incinerator, a Java virtual machine extension that introduces the notion of an outdated class loader. Incinerator detects stale references and sets them to null during a garbage collection cycle. We evaluate Incinerator in the context of the OSGi framework and show that Incinerator correctly detects and eliminates stale references, including a bug in Knopflerfish. We also evaluate the performance of Incinerator with the DaCapo benchmark on VMKit and show that Incinerator has an overhead of at most 3.3%.