嵌入式系统导论-实验课-exercise4-review.pdfVIP

Introduction to Embedded Systems Exercise 4: Resource sharing 2015.01.07 Kai Huang huangk@intum.de Resource sharing ? Examples of common resources: data structures, variables, main memory area, file, set of registers, I/O unit, ... . ? Many shared resources do not allow simultaneous accesses but require mutual exclusion (exclusive resources). A piece of code executed under mutual exclusion constraints is called a critical section. ? Can be guaranteed with semaphores S or mutexes . Resource sharing Terms Terms Priority Inversion (1) Priority Inversion (2) Solutions Resource Access Protocols Priority Inheritance Protocol (PIP) PIP: Algorithm Example: Example: Deadlock is Possible PIP---PCP PCP Example: PCP PCP : An Example PCP : An Example PCP : An Example PCP PCP : Deadlock-Free Example Exercise 4.1 Explain the difference between private , shared and exclusive resources and give an example of problems encountered in exclusive resources. Exercise 4.1 Solution: Private resources are used exclusively by one process/thread. shared resources can be used by at least two possibly competing processes/threads. exclusive resources really should always just one process/thread exclusively take on it. Exercise 4.1 Exercise 4.1 Propose three ways such that the problem occurring in Resource Sharing Problem of mutual exclusion (mutual exclusion) can be solved. Solution: Non-preemptive tasks Interrupts disabled Static scheduling Use of semaphores Exercise 4.1 Explain the application of a possible solution of the previous part. Exercise 4.2 In the lecture you learned about the Priority Inheritance Protocol (PIP). Does the PIP solve the problem of deadlocks? Give a brief explanation for your response. Solution : No, the PIP does not prevent deadlocks. Exercise 4.2 Exercise 4.2 Task: Now create a scheduling with the Priority Inheritance Protocol and fill out the chart prepared below. Highlight the critical Portions of the tasks with the letters A and B as specified