Arctic is a langu-~ge for tile specification and imp!ementation of real-time control systems. Unlike more conventional languages for real-time control, which emphasize concurrency, Arctic is a stateless language in which the relationships between system inputs, outputs and intermediate terms are expressed as operation. ~ on time-varying functions. Arctic allows discrete events or conditions to invoke and modify responses asynchronously, but because programs have no state, synchronization problems are greatly simplified. Furthermore, Arctic programs are non-sequential, and the timing of system responses is notated explicitly. This eliminates the need for the programmer to be concerned with the execution sequence, which accounts for much of the difficulty in real-time programming. 1.

The computing community needs distributed systems to satisfy its need for harnessing more computers solving more problems more quickly. Yet is still hard for programmers to write programs for such systems. Recently, configuration languages have emerged which have the aim of making distributed programming easier, more robust and more flexible. So far, each of these is confined to a small user community, and there is a wide range of features and facilities offered. In this paper, we consider the basic responsibilities of configuration languages and then look at four sample languages in detail. These are Darwin, Durra, PCL and Polylith. The study starts with simple static configuration programming and proceeds to dynamic programming and change management. The producer consumer example is used throughout, and the comparative code fragments shown are a novel feature of the paper. From the results of the comparison we deduce a ten-point scheme of criteria for evaluating a language in terms o...

This paper describes a scheme for using cache-based hardware to provide simple and efficient message passing support for message-based software systems on a tightly-coupled, shared-bus multiprocessor. This approach is based on the utilization of the existing interprocessor communications medium, the shared bus, to effect the exchange of single-word messages. Communication between processes is accomplished over logical channels using simple, blocking send and receive primitives. The physical processor/channel interface is designed so that the message transfer primitives can be implemented as single machine instructions, namely store and fetch. Special-purpose caches, called message caches, mediate channel operations and effect the exchange of messages over the shared bus.