Lecture 19: Priority handling theory Pre-emption – a high priority task’s taking of control of the CPU away from a low priority task. Priority inversion – a low priority task’s blocking of a high priority task from the CPU because of a resource it owns, thus giving it access to the CPU that the high priority task is trying to access. Unbounded priority inversion – occurrence of a high priority task blocked by a lower priority task that is itself blocked or starved by another medium priority task that has access to the CPU. Exercise 1: P T1 > P T2 > P T3 ; T1 and T3 make use of shared resource 1 (SR1) T1 ___________ _______X T2 ______________ ______________ T3 ______________ ______________ ^ ^ T3 takes SR1 T1 blocked because it needs SR1, meanwhile T2 runs Notice that T1 remains block until release of SR1 by T3. Show where pre-emption, priority inversion, and unbounded priority inversion are occurring. Possible solutions to the above problem:
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This note was uploaded on 04/07/2010 for the course ELEC ecse 421 taught by Professor Guss during the Winter '10 term at McGill.