Using Dynamic Configurability to Support Object - Oriented Languages and Systems in Legion University of Virginia Computer

Wide area distributed object systems will require mechanisms for creating, describing, and managing objects. The mechanisms must be scalable and must not mandate particular policies or algorithms because users will have different cost, security, performance, and functionality demands. Legion is a wide area distributed object system that supports this requirement using a first-class active class system. A Legion class is an active Legion object that manages its instances, provides their system-level support, and defines their behavior. To enable encapsulation and code reuse, and to simplify the requirements of many Legion programmers, Legion classes can be shared among Legion objects. To support instances that outlive the program that creates them, classes are persistent. To enable scalability, classes are distributed throughout the system. Shared, persistent, active, distributed (SPAD) class systems have many benefits for wide area distributed object systems such as Legion. But supporting traditional class roles, including instantiation and inheritance, requires new and different implementation solutions. This paper describes one way to support object-oriented languages and systems in the Legion SPAD class system. Our method is based on dynamic configurability of objects and classes. We describe dynamic configurability, motivate the need for new implementation solutions for a SPAD class system, describe the implementation of our solution, and illustrate its functionality with an example.