Bounded-wait merge in Shapiro’s Concurrent Prolog

Abstract

InA Subset of Concurrent Prolog and Its Interpreter (1983), E. Y. Shapiro introduces the language Concurrent Prolog. In his presentation, the problem of guaranteeing bounded-waiting during a merge operation is used as a programming example. Solutions are proposed for binary and n-ary merges. The solutions are, however, completely dependent on specific operational characteristics of a Concurrent Prolog machine or interpreter.

This paper presents an alternate approach in which the property of bounded-waiting is incorporated into the semantics of the programs, demonstrable given only the computational model of the language. The solution strategy is to utilize the familiar systems programming techniques of block-on-input and busy-wait. This approach requires that the language be augmented with a metalogical predicate analogous to thevar(_) predicate of Sequential Prolog. The resultant programs are interesting and illustrative examples of Concurrent Prolog as a programming language.