SERIALIZATION OF DISTRIBUTED THREADS IN JAVA']JAVA

In this paper we present a mechanism for serializing the execution-state of a distributed Java application that is implemented on a conventional Object Request Broker (ORB) architecture such as Java Remote Method Invocation (RMI). To support serialization of distributed execution-state, we developed a byte code transformer and associated management subsystem that adds this functionality to a Java application by extracting execution-state from the application code. An important benefit of our mechanism is its portability. It can transparently be integrated into any legacy Java application. Furthermore, it does require no modifications to the Java Virtual Machine (JVM) or to the underlying ORB. Our serialization mechanism can serve many purposes such as migrating execution-state over the network or storing it on disk. In particular, we describe the implementation of a prototype for repartitioning distributed Java applications at run-time. Proper partitioning of distributed objects over the different machines is critical to the global performance of the distributed application. Methods for partitioning exist, and employ a graph-based model of the application being partitioned. Our mechanism enables then applying these methods at any point in an ongoing distributed computation. In the implementation of the management subsystem, we experienced the problem of losing logical thread identity when the distributed control flow crosses address space boundaries. We solved this well known problem by introducing the generic notion of distributed thread identity in Java programming. Propagation of a globally unique, distributed thread identity provides a uniform mechanism by which all the program's constituent objects involved in a distributed control flow can uniquely refer to that distributed thread as one and the same computational entity.