Action Systems

In chapter 1 we suggested that a program be structured as a set of objects. Each object consists of actions and/or methods, where the actions are executed autonomously (following a specific execution rule) and the methods are executed when they are called. In this chapter, we consider a simpler version of this model; we eliminate the methods altogether, retaining only actions. The immediate consequence of this decision is that the objects can no longer communicate through procedure calls; we require the objects to communicate via shared variables. Actions from different objects can read/write into these variables. However, at most one action is executed at any time, so there is no possibility of concurrent write into a variable.