AN OBJECT-BASED CONCURRENT LANGUAGE ABCL/1 ON TRANSPUTERS

Abstract

With the evolution of hardware and software technology as well as the increase of computing demands, concurrency is gaining the attention in today's computer science. The primary concerns are on potential parallelism, division of tasks and synchronization. At the same time, the concept of object which provides a high level of abstraction has also emerged in different disciplines e.g. artificial intelligence, operating systems. The fusion of these two fields gives rise to a new programming paradigm - concurrent object-oriented language such as ABCL/1 (An object-Based Concurrent Language). ABCL/1 (An object-Based Concurrent Language) is the description language of the object-based concurrent model ABCM/1. Its main purpose is to exploit both the source of computation power i.e. parallelism and the source of modeling power i.e. object-orientation. This thesis discusses the concurrent model ABCM/ I, its description language, ABCL/1, and the transputer-based parallel realization of ABCL – ABCL/T. The keywords of' the object-based concurrent system are self-containedness and message-based computation. A real world problem can be represented as a collection of concurrent objects and the interactions among them. The inherent parallelism can be fully exploited with a suitable parallel architecture e.g. transputer-based MIMD machine. ABCL/T is designed to fully exploit the underlying transputer's RISC-like architecture, hardware-support scheduling and the high speed communicating facilities namely, point-to-point named channels. The kernel of ABCL/T is compartmentalized into a number of kernel objects which are implemented as encapsulated data structures. The kernel data is distributed and accessed through the respective kernel object in a clean, unified and protected manner. This approach thus increases the level of concurrency and manageability within the kernel. A concurrent object is an autonomous information agent as well as a unit of execution. It encompasses its own methods, virtual processor and its local slates, if any. It executes concurrently and in cooperation with the other objects. In addition, it is mapped directly onto the transputer process so as to fully exploit the computing power of the underlying machine. Concurrent objects are created dynamically and automatically garbage-collected. Dynamic memory management, concurrent object management and transparent garbage collection mechanism are incorporated in the kernel to facilitate efficient execution of objects. All objects are evenly distributed according to the built-in load balancing scheme over a network of transputers. This thus manifests the parallelism of the computation model. In addition, intra-object concurrency is incorporated in ABCL/T to further increase the level of concurrency. The interactions among objects are via message passing only. Three types of mechanisms, namely, past (asynchronous), now (synchronous) and future (eager) types are included to enable inter-object communications.