Exception Handling and Asynchronous Active Objects: Issues and Proposal

Asynchronous Active Objects (AAOs), primarily exempli ed by actors [1], nowadays exist in many forms (various kinds of actors, agents and components) and are more and more used because they t well the dynamic and asynchronous nature of interactions in many distributed systems. They raise various new issues regarding exception handling for which few operational solutions exist. More precisely, a need exists for a generic, simple and expressive, programmer level, exception handling system that appropriately handles the following main exception handling issues or requirements in the context of AAOs: encapsulation, object autonomy, coordination of concurrent collaborative entities [2], caller contextualization [3], asynchronous signaling and handler execution, resolution of concurrent exceptions [4,5], exception criticality [6] and object reactivity. This paper presents the speci cation of an evolution of the Sage exception handling system [7], which provides solutions to those issues in the context of systems developed with active objects using one way asynchronous communications and interacting via the request / response protocol. Such a context, in which synchronizations constraints are, when needed, handled at the application level, allows for a very generic view of what could be done regarding exception handling in all systems that use active objects. The Sage solution is original and provides a good compromise between expressive-power and simplicity.