[ Pintos ] 1.Threads: Priority Scheduling

Main Goal

Pintos uses FIFO scheduling

Modify PintOS scheduler for priority scheduling

• Sort the ready list by the thread priority
• Sort the wait list for synchronization primitives(semaphore, condition variable)
• Implement the preemption
• Preemption point: ehwn the thread is put into the ready list(not everytime when the timer interrupt is called)

Three things to consider

1: selecting

when selecting a thread to run in the ready list, select one with the highest priority

2: Preemption

when inserting the new thread to the ready list, compare the priority with the running thread.

Schedule the newly inserted thread if it has the higher priority with the currently running thread

3: Lock - semaphore, condition variable

when selecting a thread from the set of threads wating for a lock(or condition variable), select the one with the highest priority