Jawaban Quiz 23/08/05 - Soal 3

Topik-topik yang pernah dibahas dalam kuliah

Liveline

Other than deadline, we should also consider liveline or startline as a time constraint factor in a real-time system. There are some cases where the start time is also crucial.

Priority Inversion

Priority inversion happens when a task of lower priority able to delay or preempt other task of higher priority. This may happen when the higher priority task try to access a critical section which is currently locked by the lower priority task.

Priority Inheritance

Priority inheritance is a protocol used to avoid the problem of priority inversion. When a lower priority task is blocking a higher priority task, it inherits the priority of the higher priority task. It gains its priority back when the blocking is over. The bad side of priority inversion is that it can lead to deadlock.

Priority Ceiling

Priority ceiling is a protocol used to avoid deadlock caused by priority inheritance. Basically, it is the same as priority inheritance. The difference is that there is another factor that determine the blocking of a task from entering a critical section. Each critical section has a semaphore. The priority ceiling of the semaphore is the same as the highest priority task that may access the critical section. A task is blocked from entering a critical section when there is a semaphore currently held by a task whose priority ceiling is higher or equal to its priority.