Creating operating system components and subsystcms in today's large processors generally requires dealing with more than one CPU operating in parallel against a shared memory. While "applications" are typically shielded from the effects of parallelism, components and subsystems ususally are designed in such a way that some level of understanding is required. This paper concentrates on the pitfalls awaiting the proprammer in a parallel (or even a multiprogramming) environment when shared data structures (control blocks) are referenced and altercd by muitipie processes (tasks). The focus is on the IBM Systemi 370 architecture because of its multiple CPU architecture and the powerful "compare and swap" instruction. The paper reviews some architectural groundrules that a parallel programmer must understand, presents problems that must often be solved in a parallel environment, then describes solutions such as usage of compare and swap, locks, and single-process schemes. Kernels of code are used to illustrate problems and solutions.
By: R. Kent Treiber
Published in: RJ5118 in 1986
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