Debugging Techniques for Communicating, Loosely-Coupled Processes

Thesis (Ph. D.)--University of Rochester. Dept. of Computer Science, 1981. Simultaneously published in the Technical Report series.This thesis describes work done on debugging techniques and tools for communicating, loosely-coupled processes. Our work is intended to reduce the apparent complexity of large systems of communicating programs by regarding only the interprocess activities of such programs. The use of multiple, communicating processes as a model of computation allows for a very clean "cut" of what information is interesting for debugging and what is not. Our approach to debugging is to provide the user with information about how sets of these processes behave rather than what each program associated with each process does. Our tools provide various primitives for manipulating the interprocess activities of processes. We provide nothing to access the source code of any program. Our tools include a debugger program, a mechanism to fire and execute interprocess debugging demons and the ability to obtain transcripts of interprocess activities. The debugger provides commands for the user at a terminal for creating and manipulating individual interprocess events. Demons are an event-driven mechanism used to automatically monitor and modify interprocess events. Transcripts provide a record of interprocess events that can be replayed later. Our debugging techniques make use of these tools to provide individual process control, communication monitoring and process testing. Process control includes the ability to create, suspend and destroy processes as well as the ability to obtain various process-related information. The communication monitoring facility monitors message traffic and can dynamically alter the contents of these messages. Process testing allows a user to isolate a process (or simulate a process) by creating and intercepting all message traffic in and out of a process. This thesis also describes a debugging system called SPIDER that was built to demonstrate the above debugging tools and techniques. A multi-process kernel is included in SPIDER that supports communicating, loosely-coupled processes. SPIDER also includes an implementation of each of our proposed tools: a debugger program, a mechanism for firing demons and a transcriber. Several examples using SPIDER are given to show how our debugging techniques can be achieved with our debugging tools . .