public interface Delayed extends Comparable<Delayed> {
 
     /**
      * Returns the remaining delay associated with this object, in the
      * given time unit.
      *
      * @param unit the time unit
      * @return the remaining delay; zero or negative values indicate
      * that the delay has already elapsed
     */
    long getDelay(TimeUnit unit);
}

 // 鎖。
 private final transient ReentrantLock lock = new ReentrantLock();
 // 優(yōu)先隊(duì)列。
 private final PriorityQueue<E> q = new PriorityQueue<E>();
 
 /**
  * Leader-Follower的變種。
  * Thread designated to wait for the element at the head of
  * the queue.  This variant of the Leader-Follower pattern
 * (http://www.cs.wustl.edu/~schmidt/POSA/POSA2/) serves to
 * minimize unnecessary timed waiting.  When a thread becomes
 * the leader, it waits only for the next delay to elapse, but
 * other threads await indefinitely.  The leader thread must
 * signal some other thread before returning from take() or
 * poll(...), unless some other thread becomes leader in the
 * interim.  Whenever the head of the queue is replaced with
 * an element with an earlier expiration time, the leader
 * field is invalidated by being reset to null, and some
 * waiting thread, but not necessarily the current leader, is
 * signalled.  So waiting threads must be prepared to acquire
 * and lose leadership while waiting.
 */
private Thread leader = null;

/**
 * Condition signalled when a newer element becomes available
 * at the head of the queue or a new thread may need to
 * become leader.
 */
// 條件，代表如果有數(shù)據(jù)則通知Follower線程，喚醒線程處理隊(duì)列內(nèi)容。
private final Condition available = lock.newCondition();

 public boolean offer(E e) {
     // 獲取到鎖
     final ReentrantLock lock = this.lock;
     lock.lock();
     try {
         // 將元素存儲(chǔ)到PriorityQueue優(yōu)先隊(duì)列中
         q.offer(e);
         // 如果第一個(gè)元素是當(dāng)前元素，說明之前隊(duì)列中為空，則先將Leader設(shè)置為空，通知等待線程可以爭(zhēng)搶Leader了。
         if (q.peek() == e) {
            leader = null;
            available.signal();
        }
        // 返回成功
        return true;
    } finally {
        lock.unlock();
    }
}

public void put(E e) {
    offer(e);
}

 public E take() throws InterruptedException {
     final ReentrantLock lock = this.lock;
     // 獲取可中斷的鎖。
     lock.lockInterruptibly();
     try {
         // 循環(huán)獲取數(shù)據(jù)。
         for (;;) {
             // 獲取最早過期的元素，但是不彈出對(duì)象。
             E first = q.peek();
            // 如果最早過期的元素為空，說明隊(duì)列為空，則線程直接進(jìn)入無限期等待，并且讓出鎖。
            if (first == null)
                // 當(dāng)前線程無限期等待，直到被喚醒，并且讓出鎖對(duì)象。
                available.await();
            else {
                // 獲取最早過期的元素剩余過期時(shí)間。
                long delay = first.getDelay(NANOSECONDS);
                // 如果剩余過期時(shí)間小于0，則說明已經(jīng)過期，反之還沒有過期。
                if (delay <= )
                    // 如果已經(jīng)過期直接獲取最早過期的元素，并返回。
                    return q.poll();
                // 如果剩余過期日期大于0，則會(huì)進(jìn)入到這里。
                // 將剛才獲取的最早過期的元素設(shè)置為空。
                first = null; // don't retain ref while waiting
                // 如果有線程爭(zhēng)搶的Leader線程，則進(jìn)行無限期等待。
                if (leader != null)
                    // 無限期等待并讓出鎖。
                    available.await();
                else {
                    // 獲取當(dāng)前線程。
                    Thread thisThread = Thread.currentThread();
                    // 設(shè)置當(dāng)前線程變?yōu)長(zhǎng)eader線程。
                    leader = thisThread;
                    try {
                        // 等待剩余等待時(shí)間。
                        available.awaitNanos(delay);
                    } finally {
                        // 將Leader設(shè)置為null。
                        if (leader == thisThread)
                            leader = null;
                    }
                }
            }
        }
    } finally {
        // 如果隊(duì)列不為空，并且沒有Leader則通知等待線程可以成為L(zhǎng)eader。
        if (leader == null && q.peek() != null)
            // 通知等待線程。
            available.signal();
        lock.unlock();
    }
}

 public E poll() {
     final ReentrantLock lock = this.lock;
     lock.lock();
     try {
         E first = q.peek();
         // 如果隊(duì)列為空或者隊(duì)列最早過期的元素沒有過期，則返回null。
         if (first == null || first.getDelay(NANOSECONDS) > 0)
             return null;
         else
            // 出隊(duì)列操作。
            return q.poll();
    } finally {
        lock.unlock();
    }
}