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/*
 * $Id$
 */

/*

Copyright (c) 2000-2003 Board of Trustees of Leland Stanford Jr. University,
all rights reserved.

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
STANFORD UNIVERSITY BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR
IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

Except as contained in this notice, the name of Stanford University shall not
be used in advertising or otherwise to promote the sale, use or other dealings
in this Software without prior written authorization from Stanford University.

*/

package org.lockss.util;

import java.util.*;

import org.lockss.util.time.Deadline;

/**
 * Queue interface.
*/
public interface Queue {

  /**
   * Add to the queue. */
  public Object put(Object obj);

  /**
   * Remove first element from the queue. Does not return until
   * an object appears in the queue or the timer expires.
   * @return The element formerly at the head of the queue
   */
  public Object get(Deadline timer) throws InterruptedException;

  /**
   * Return first element on queue, without removing it.
   * @return The element at the head of the queue, or null if queue is empty
   */
  public Object peek();

  /**
   * Wait until the queue is non-empty, then return the element at the
   * head of the queue, leaving it on the queue.
   * @return the item at the head of the queue, or null if a
   * timeout occurred before an item was available.
   * @throws InterruptedException if interrupted while waiting
   */
  public Object peekWait(Deadline timer) throws InterruptedException;

  /**
   * Remove the specified element from the queue.  If the element appears
   * in the queue more than once, the behavior is undefined.
   * @return true iff the element was present in the queue
   */
  public boolean remove(Object obj);

  /**
   * Return the number of elements in the queue
   */
  public int size();

  /**
   * Return true iff the queue is empty
   */
  public boolean isEmpty();

  /**
   * Return a snapshot of the queue contents
   */
  public List copyAsList();

}