Abstract Event Synchronization Analysis for Debuggi:ng Parallel Programs *

One of the major difficulties of explicit parallel pro-gramming for a shared memory machine model is de-tecting the potential for nondeterminacy and identi-fying its causes. There will often be shared variables in a parallel program, and the tasks comprising the program may need to be synchronized when accessing these variables. This paper discusses this problem and presents a method for automatically detecting non-determinacy in parallel programs that utilize event style synchro-nization instructions, using the Post, Wait, and Clear primitives. With event style synchronization, espe-cially when there are many references to the same event, the difficulty lies in computing the execution order that is guaranteed given the synchronization in-structions and the sequential components of the pro-gram. The main result in this paper is an algorithm that computes such an execution order and yields a Task Graph upon which a nondeterminacy detection algorithm can be applied. We have focused on events because they are a frequently used synchronization mechanism in par-allel versions of Fortran, including Cray [Cray87]