Exception Handling and Asynchronous Active Objects: Issues and Proposal

Abstract

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.

Who is Accountable for Asynchronous Exceptions?

“…The handler can either be defined in the supplier or it can come from the client via an argument. Supplier-specific handlers are common: any mechanism where a supplier can deal with an exception in a local handler falls into this category; one example is SaGE [5]. Call-specific handlers are less common, but there are mechanisms, such as JR [6], using this approach.…”

“…Propagation is always enabled. Examples include SaGE [5] with its client-based handlers, Erlang [4] with its exit signals over process links, Arche [11] where a client propagates exceptions as a result of incoming method calls, and ARMI [12] with its callback mechanism.…”

“…These instantiations of the framework describe abstract approaches and not concrete mechanisms. To show how the framework can be applied to a concrete mechanism, Section III-B instantiates the framework for µC++ [3], Section III-C for Erlang [4], and Section III-D for SaGE [5].…”

“…SaGE [5] is an exception mechanism for languages using the active object pattern [32]. The active object pattern provides a solution to decouple an invocation in one object from the resulting execution in another object by giving an own thread of control to each object; the pattern is often used to implement the actor model [31].…”

“…The framework offers concepts to describe asynchronous exception mechanisms. Its applicability is shown on a number of mechanisms: µC++ [3], Erlang [4], and SaGE [5].…”