Multiple times in systems: a perspective

Summary form only given. Time plays a fundamental role in real-time computer controlled systems, in which the system dynamics depend on the temporal behavior of controlling tasks. The temporal behavior of the tasks, in turn, is determined through the system level policies which are designed to execute the tasks in a timely manner by preserving the time constraints on their execution. We show that by maintaining multiple temporal views for resources and tasks, the behavior of system policies for resource management, scheduling, and fault tolerance can be explained in simple intuitive ways. The temporal views of resources and tasks are related to the notion of real-time, through the use of clock time. The concept is easily generalizable to distributed environments, wherein factors such as clock skew, communication times etc. must also be incorporated. We present examples to illustrate the concept and benefits of maintaining multiple temporal views in systems