An Experimental Implementation of Action-Based Concurrency

Abstract

This thesis reports on an implementation of an action-based model for concurrent programming. Concurrency is expressed by allowing objects to have actions with a guard and a body. Each action has its own execution context, and concurrent execution is realized when program execution is happening in more than one context at a time. Two actions of different objects can run concurrently, and they are synchronized whenever a shared object is accessed simultaneously by both actions. The appeal of this model is that it allows a conceptually simple framework for designing and analyzing concurrent programs. To experiment with action-based concurrency, we present a small language, ABC Pascal, which is an experimental attempt as a proof of feasibility of such a model, and also meant to help identify issues for achieving reasonable efficiency in implementation. It extends a subset of Pascal that supports basic sequential programming constructs, and provides action-based concurrency as the action-based model prescribes. This work deals with the specification and implementation of ABC Pascal. The one-pass compiler directly generates assembly code, without devoting efforts to optimization. While the code is not optimized, the results that ABC Pascal has achieved in performance testing are so far comparable to mainstream concurrent programming languages.