PDG: A process-level debugger for concurrent programs in the GRAPE parallel programming environment

In this paper, we describe the process-level debugger of GRAPE, our hierarchical graphical programming environment for concurrent programs. Its unique feature is that it clearly separates the identification of erroneous processes, which we call process-level debugging, from the exact localisation of the bug at the source-level. This divide-and-conquer approach is absolutely necessary for debugging complex parallel programs in a fast and systematic way. Our processlevel debugging approach is based on an animation of the program's behaviour on its hierarchical graphical representations. Graphical views are used that reflect the programmer's mental picture of the actual application. Hierarchy allows us to employ a top-down debugging approach in which we successively refine the search-space by zooming in on suspect processes first-time-right. During animation a debugging kernel implementing a record-replay mechanism guarantees reproducible program behaviour.