A Compiler and Symbolic Debugger for Occam

Abstract

We have implemented Occam, a parallel programming language, on a uniprocessor machine (MC-68020 based HORIZON I11 running on UNIX system V.2) with simulated concurrency. Occam is a descendant of CSP with a few convenient modifications like channels used for communication and procedures. Two additions to the original language, i.e., output guards and recursion have been proposed. Front end of the compiler was developed using LEX and YACC. An innovative code generator, generator based on tree pattern matching has been used to generate the back end of the compiler, which generates efficient MC-68020 assembly code. A kernel for process administration is the runtime support provided. It has been developed entirely in ' C ' and made available as a library. This is linked with the assembly module to generate the executable version of the input Occam program. We have also interfaced our Occam compiler with Unix system V.2 source level debugger 'Sdb' so as to provide debugging support for Occam programmers. Issues involved in parallel debugging have been investigated and those demanding minimum effort have been incorporated in Occam debugger by modifying the runtime support of the uniprocessor implementation. Modifications to the uniprocessor implementation so as to make it run on a shared memory multiprocessor machine(HCL MAGNUM-P with four MC-68030 processors) are also discussed. The support provided by MAGNUM-P at the architecture and operating system levels is explained in detail. Our Occam compiler for the multiprocessor generates code, but the generated code has not been tested since the machine is not yet ready.