Java源码解析阻塞队列ArrayBlockingQueue常用方法

  /** The queued items **/  final Object[] items;  /** items index for next take, poll, peek or remove **/  int takeIndex;  /** items index for next put, offer, or add **/  int putIndex;  /** Number of elements in the queue **/  int count;  /**   * Concurrency control uses the classic two-condition algorithm   * found in any textbook.   **/  /** Main lock guarding all access **/  final ReentrantLock lock;  /** Condition for waiting takes **/  private final Condition notEmpty;  /** Condition for waiting puts **/  private final Condition notFull;  /**   * Shared state for currently active iterators, or null if there   * are known not to be any. Allows queue operations to update   * iterator state.   **/  transient Itrs itrs = null;

  /**   * Inserts the specified element at the tail of this queue, waiting   * for space to become available if the queue is full.   * @throws InterruptedException {@inheritDoc}   * @throws NullPointerException {@inheritDoc}   **/  public void put(E e) throws InterruptedException {    checkNotNull(e);    final ReentrantLock lock = this.lock;    lock.lockInterruptibly();    try {      while (count == items.length)        notFull.await();      enqueue(e);    } finally {      lock.unlock();    }  }  /**   * Inserts element at current put position, advances, and signals.   * Call only when holding lock.   **/  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++;    notEmpty.signal();  }

  /**   * Inserts the specified element at the tail of this queue if it is   * possible to do so immediately without exceeding the queue's capacity,   * returning {@code true} upon success and {@code false} if this queue   * is full. This method is generally preferable to method {@link #add},   * which can fail to insert an element only by throwing an exception.   * @throws NullPointerException if the specified element is null   **/  public boolean offer(E e) {    checkNotNull(e);    final ReentrantLock lock = this.lock;    lock.lock();    try {      if (count == items.length)        return false;      else {        enqueue(e);        return true;      }    } finally {      lock.unlock();    }  }

  public E take() throws InterruptedException {    final ReentrantLock lock = this.lock;    lock.lockInterruptibly();    try {      while (count == 0)        notEmpty.await();      return dequeue();    } finally {      lock.unlock();    }  }