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在许多实时系统中,同一个计算平台上往往既有硬实时关键计算任务又有软实时非关键计算任务。硬实时任务必须在规定时间内完成,否则将导致系统错乱或崩溃等严重后果。而软实时任务若没有在规定时间内完成,虽会影响系统性能,但不会造成重大后果。为确保每个硬实时任务均在其规定时间内完成,在某些情况下需要拒绝一些软实时任务进入任务队列。文章提出了一种基于控制器自动合成策略的解决方案,通过所设计的准入控制器,对系统产生的每一个新任务自动决定是否准其进入任务队列。准入控制器必须使得所有被准入的任务均在规定时间内完成,并且决策序列满足以线性时态逻辑描述的服务质量要求。文章的主要贡献是提出了判定是否存在准入控制器的算法,该算法能在判定结果为真时构造出一个以有限状态时间自动机表达的准入控制器。
In many real-time systems, the same computing platform often has both hard real-time critical computing tasks and soft real-time non-critical computing tasks. Hard real-time tasks must be completed within the prescribed time, otherwise it will lead to system disruption or collapse and other serious consequences. The soft real-time tasks, if not completed within the stipulated time, will affect system performance, but will not cause serious consequences. To ensure that each hard real-time task is completed within its allotted time, in some cases it is necessary to reject some soft real-time tasks into the task queue. This paper presents a solution based on automatic controller synthesis strategy. Through the designed admission controller, every new task generated by the system automatically decides whether or not to admit it into the task queue. The admission controller must have all of the admitted tasks completed within the specified time, and the decision sequence satisfies the quality of service requirements described in linear temporal logic. The main contribution of the paper is to propose an algorithm to determine whether there is a admittance controller. The algorithm can construct an admission controller expressed in finite state time automata when the result of the decision is true.