PAL: Exploiting Java annotations for parallelism

We discuss how Java annotations can be used to provide the meta information needed to automatically transform plain Java programs into suitable parallel code that can be run on workstation clusters, networks and grids. Programmers are only required to decorate the methods that will eventually be executed in parallel with standard Java 1.5 annotations. Then these annotations are automatically processed and parallel byte code is derived. When the annotated program is started, it automatically retrieves the information about the executing platform and evaluates the information specified inside the annotations to transform the byte-code into a semantically equivalent multithreaded or multitask version, depending on the target architecture features. The results returned by the annotated methods, when invoked, are futures with a wait-by-necessity semantics. A PAL (Parallel Abstraction Layer) prototype exploiting the annotation based parallelizing approach has been implemented in Java. PAL targets JJPF, an existing, skeleton based, JAVA/JINI programming environment, as Parallel Framework. The experiments made with the prototype are encouraging: the design of parallel applications has been greatly simplified and the performances obtained are the same of an application directly written in JJPF.