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Real-Time Concepts for Embedded SystemsThis action ends the priority inversion at time t4. The HP-task continues its execution, however, even when it releases the resource at t5. This is the nature of the priority-based, preemptive scheduling scheme. The HP-task runs because it has the highest priority in the system. The priority inheritance protocol is dynamic because a task does not have its priority raised until a higher-priority task makes a request on the shared resource. An unrelated higher-priority task can still preempt the task, which is the nature of the priority-based, preemptive scheduling scheme. The priority promotion for a task during priority inversion is transitive, which means the priority of a promoted task continues to rise even if higher-priority tasks make requests on the same shared resource while priority inversion is taking place, as shown in Figure 16.9. Figure 16.9: Transitive priority promotion example. In this example, three tasks with differing priorities share a resource. The LP-task acquires the resource first at time t1 ...» |
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