From Objects to Actors: Study of a Limited Symbiosis In Smalltalk-80

Abstract

In this paper we describe an implementation of actors in Smalltalk-80, named Actalk. This attempt is designed as a minimal extension preserving the Smalltalk-80 language.Actors are active and autonomous objects, as opposed to standard passive Smalltalk-80 objects. An actor is built from a standard Smalltalk-80 object by associating a process with it and by serializing the messages it could receive into a queue.We will study the cohabitation and synergy between the two models of computation: transfer of active messages 1989 between passive objects, and exchange of passive messages between active objects. We propose a sketch of methodology in order to have a safe combination between these two programming paradigms.We show how to extend the Actalk kernel into various extensions to define the basic Actor model of computation, higher level programming constructs such as the 3 types of message passing (asynchronous, synchronous, and eager) proposed in the ABCL/1 programming language, and distributed architectures. All these examples are constructed as simple extensions (by using inheritance) of our kernel model. © 1989, ACM. All rights reserved.