A visual approach to specifying message-passing operations

Visual programming is a very promising approach for parallel programming because of the complexity in making parallel programs. There were several attempts to provide a visual environment for making parallel programs but only achieved a limited success. The commonly used technique is to draw some graphs whose nodes represent modules and arcs represent some communication paths. The graphs are then annotated by attaching some conventional programming codes. In practice, this approach can be useful but in a limited number of cases. To improve the situation, a new visual programming environment is being developed that allows the creation of programs from algorithmic "film" specifications with a minimal use of text in making programs. In this environment, there are six different groups of frames for the programmer to watch, edit, and specify operations. One of them is for specifying I/O operations and communication between software components in a complex program. Specifying communications among processes in a parallel program is just a partial case in this subsystem. This paper presents a visual environment for specifying communication among processes in a parallel program using a language of micro-icons. As an example, the scatter and gather types of collective communication are presented based on the master/slave scheme of computation. These examples show how to define message-passing communication without using text-based programming style.