Jada: Coordination and communication for java agents

Abstract

In this chapter we are going to analyze mobile code issues in the perspective of object oriented systems in which thread migration is not supported. This means that both object's code and data can be transmitted from a place to another but not the current execution state (if any) associated to the object. This is the case with the Java language which is often used in the Word Wide Web for developing applets which are little applications downloaded on the fly and executed in the client machine. While this meehanism is quite useful for enhancing HTML documents with sound and animation, we think that this teehnology can give its best in the field of distributed-cooperative work, both in the perspective of Intemet and Intranet connectivity. Java is indeed a concurrent, multithreaded language, but it offers little help for distributed programming. Thus, we introduce Jada, a coordination toolkit for Java where coordination among either concurrent threads or distributed Java objects is achieved via shared object spaces. By exchanging objects through tuple spaces, Java programs and applets can exchange data or synchronize their actions over a single host, a LAN, or even the Intemet. The access to an object space is performed using a set of methods of the Obj ectSpace class. Such operations are out (to put an object in the object space), in and read (to get or to read associatively an object from the object space), and others, mostly inspired by the Linda language. Jada does not extends the syntax of Javabecause it is a set of classes. We show how it changes the way we design multiuser, distributed applications (such as the ones based on the WWW) allowing easy interactions between software components and agents. Under this perspective we can outline a system of any scale which uses the dynamic linking capability of Java to distribute the code and the coordination facility of Jada to handle distributed entities inter-relations.