3-D visualization of message passing in distributed programs

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This paper describes PVMtrace, a software system for understanding and debugging message passing in distributed programs. In this system each process is represented as a node in a graph and the arcs represent the potential communication channels. The transfer of a packet of information from one process to another is shown by a bead-like object moving along an arc. A queue is a string of beads lined up waiting to be processed. The flexible control over time is found to be essential for the system to be useful and it allows the animation to be played forward and backwards in time both by the direct manipulation of the time line and by an animation rate controller. In addition there is an automatic time control method that rapidly moves the animation through intervals of low activity while slowing down in periods of high activity. The system was initially developed as a PVM debugging tool but it has also been found to be useful in other areas. In particular it has been used to visualize communications in a cellular phone system.