Non-busy-timer-sleep

Keep old timer_sleep function(a busy sleep).

Use semaphore to implement non-busy-sleep

Maintain a list and a node:

struct timer_wait_node{  
    struct semaphore sem;  
    struct list_elem elem;  
    struct thread *t;  
};

Add a new field in thread to record finish time: finish

How to sleep?

void timer_non_busy_sleep(int microSecounds); compute a wake up time:
t->finish = timer_get_timestamp() + microSecounds; put a timer_wait_node(say twn) back to the timer wait list
semaphore down twn and it will sleep

How to wake up?

wake_up function:
go through the timer_wait_list and find the thread which should wake up by comparing the finish time and current time.
If current time is later--->the thread should wake

where to wake up?

schedule
calling schedule function will first check wait list
waked thread will finally run

  wake_up();  
...  
}