在实时系统中消除优先级反向

Deleting Priority Inversion in Real-Time Systems

优先级反向是实时系统中由任务间需要同步引起的高优先级任务被低优先级任务阻塞的现象．优先级反向使得高优先级实时任务被阻塞的时间是不确定的，增加了实时系统的不确定性．分析解决了优先级反向的方法─基本优先级继承和优先级上限的特性．两者相比，后者使高优先级任务的阻塞时间缩短到不超过一个极大临界段的执行时间．并给出在最差情形下判定周期任务集可调度的一个充分条件．

Priority inversion is a phenomenon that a high priority real-time task is blocked by low priority real-time tasks because of synchronization among these tasks. It makes the high priority task blocked for a nondeterministic period of time and resultS in the nondeterminism of real-time dystems. Two solutions to this problem are proposed, basic priority inheritance protocol and priority ceiling protocol. Their performances are analyzed. Compared with the former one, the later one makes the period of time when the high priority task is blocked and does not exceed the execution time of the largest critical section. A sufficient condition is given to determine whether a set of periodic tasks is schedulable in the worst situation.