PDG : A Process-Level Debugger in GRAPE for communicating processes on transputer platforms*

In this paper, we describe the process-level debugger of GRAPE, a hierarchical graphical programming environment for concurrent programs. This debugger allows to debug concurrent programs that are based on communicating sequential processes. Its unique feature is that it clearly separates the identification of erroneous processes from the exact localisation of the bug on the source-level. This divide-and-conquer approach is absolutely necessary for debugging complex parallel programs in a fast and systematic way. Our process-level debugging approach is based on an animation of program behaviour on its hierarchical graphical representation. Graphical views are used that reflect the programmer's mental picture of the 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-timeright. During animation, a debugging kernel implementing a record-replay mechanism guarantees reproducible program behaviour for programs containing races and asynchronous