java中阻塞隊列詳細介紹

public class ArrayBlockingQueue<E> extends AbstractQueue<E>
 implements BlockingQueue<E>, java.io.Serializable {
 
 /** The queued items */
 //以數組的結構存儲隊列的元素，采用的是循環數組
 final Object[] items;

 /** items index for next take, poll, peek or remove */
 //隊列的隊頭索引
 int takeIndex;

 /** items index for next put, offer, or add */
 //隊列的隊尾索引
 int putIndex;

 /** Number of elements in the queue */
 //隊列中元素的個數
 int count;

 /** Main lock guarding all access */
 //對于ArrayBlockingQueue所有的操作都需要加鎖，
 final ReentrantLock lock;

 /** Condition for waiting takes */
 //條件隊列，當隊列為空時阻塞消費者并在生產者生產后喚醒消費者
 private final Condition notEmpty;

 /** Condition for waiting puts */
 //條件隊列，當隊列滿時阻塞生產者，并在消費者消費隊列后喚醒生產者
 private final Condition notFull;
}

 /**
 * 向隊列中添加元素
 * 當隊列已滿時需要阻塞當前線程
 * 放入元素后喚醒因隊列為空阻塞的消費者
 */
 public void put(E e) throws InterruptedException {
 checkNotNull(e);
 final ReentrantLock lock = this.lock;
 lock.lockInterruptibly();
 try {
  //當隊列已滿時需要notFull.await()阻塞當前線程
  //offer(e,time,unit)方法就是阻塞的時候加了超時設定
  while (count == items.length)
  notFull.await();
  //放入元素的過程
  enqueue(e);
 } finally {
  lock.unlock();
 }
 }
 
 /**enqueue實際添加元素的方法*/
 private void enqueue(E x) {
 // assert lock.getHoldCount() == 1;
 // assert items[putIndex] == null;
 final Object[] items = this.items;
 items[putIndex] = x;
 if (++putIndex == items.length)
  putIndex = 0;
 count++;
 //如果條件隊列中存在等待的線程
 //喚醒
 notEmpty.signal();
 }

 /**
 * 從隊列中獲取元素
 * 當隊列已空時阻塞當前線程
 * 從隊列中消費元素后喚醒等待的生產線程
 */
 public E take() throws InterruptedException {
 final ReentrantLock lock = this.lock;
 lock.lockInterruptibly();
 try {
  //隊列為空需要阻塞當前線程
  while (count == 0)
  notEmpty.await();
  //獲取元素的過程
  return dequeue();
 } finally {
  lock.unlock();
 }
 }
 
 /**dequeue實際消費元素的方法*/
 private E dequeue() {
 // assert lock.getHoldCount() == 1;
 // assert items[takeIndex] != null;
 final Object[] items = this.items;
 @SuppressWarnings("unchecked")
 E x = (E) items[takeIndex];
 items[takeIndex] = null;
 if (++takeIndex == items.length)
  takeIndex = 0;
 count--;
 if (itrs != null)
  itrs.elementDequeued();
 //消費元素后從喚醒阻塞的生產者線程
 notFull.signal();
 return x;
 }