Function add_timer

os/src/timer.rs:57–60

(expire_ms: usize, task: Arc<TaskControlBlock>)

}

pub fn add_timer(expire_ms: usize, task: Arc<TaskControlBlock>) {
    let mut timers = TIMERS.exclusive_access();
    timers.push(TimerCondVar { expire_ms, task });
}

pub fn check_timer() {
    let current_ms = get_time_ms();