Experiments with Program Parallelization Using Archetypes and Stepwise Refinement

Parallel programming continues to be difficult and errorprone, whether starting from specifications or from an existing sequential program. This paper presents (1) a methodology for parallelizing sequential applications and (2) experiments in applying the methodology. The methodology is based on the use of stepwise refinement together with what we call parallel programming archetypes (briefly, abstractions that capture common features of classes of programs), in which most of the work of parallelization is done using familiar sequential tools and techniques, and those parts of the process that cannot be addressed with sequential tools and techniques are addressed with formally-justified transformations. The experiments consist of applying the methodology to sequential application programs, and they provide evidence that the methodology produces correct and reasonably efficient programs at reasonable human-effort cost. Of particular interest is the fact that the aspect of the methodology that is most completely formally justified is the aspect that in practice was the most trouble-free.