Linda and Friends

Abstract

Linda consists of a few simple operators designed to support and simplify the construction of explicitly-parallel programs. Linda has been implemented on ATandT Bell Labs' S/Net multicomputer and, in a preliminary way, on an Ethernet-based MicroVAX network and an Intel iPSC hypercube. Parallel programming is often described as being fundamentally harder than conventional, sequential programming, but in our experience (limited so far, but growing) it isn't. Parallel programming in Linda is conceptually the same order of task as conventional programming in a sequential language. Parallelism does, though, encompass a potentially difficult problem. A conventional program consists of one executing process, of a single point in computational time-space, but a parallel program consists of many, and to the extent that we have to worry about the relationship among these points in time and space, the mood turns nasty. Linda's mission, however, is to make it largely unnecessary to think about the coupling between parallel processes. Linda's uncoupled processes, in fact, never deal with each other directly. A parallel program in Linda is a spatially and temporally unordered bag of processes, not a process graph.