Controlled scheduling of program threads in a multitasking operating system

摘要

A multitasking operating system permits application programs (and their developers) to influence a schedule of execution of program threads derived from the application programs. Each of the program threads is assigned a priority level and a dispatch class in which the thread resides. Based on these parameters, the operating system schedules the threads for execution in the following manner. The operating system queues the highest priority thread which is available for execution from each dispatch class onto a run list for execution by a processor. The highest priority thread on the run list is executed first. An application program thread can change the dispatch class in which another program thread resides. An executing program thread can also voluntarily yield to a specified program thread in the same dispatch class or permit the highest priority available thread in the same dispatch class to be queued on the run list with itself being available and in contention for the run list.