Semantics of prialt in Handel-C~(TM)

摘要

This paper discusses the semantics of the prialt construct in Handel-C. The language is essentially a static subset of C, augmented with a parallel construct and channel communication, as found in CSP. All assignments and channel communication events take one clock cycle, with all updates synchronised with the clock edge marking the cycle end. The behaviour of prialt in Handel-C is similar in concept to that of Occam, and to the p-priority concept of Adrian Lawrence CSPP. However, we have to contend with both input and output guards in Handel-C, unlike the situation in Occam, although prialts with conflicting priority requirements are not legal in Handel-C. This makes our problem simpler than the more general case including such conflicts considered in [4]. We start with an informal discussion of the issues that arise when considering the semantics of Handel-C's prial c construct. We define a resolution function (R) that determines which requests in a collection of prial ts become active. We describe a few properties that we expect to hold for resolution, and discuss the issue of compositionality.