/*

 * Copyright (c) 2000, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 *

 */

package sun.jvm.hotspot.utilities;

/** The backend for the message queue abstraction. This class is

    instantiated first and queried to provide the two "sides" of the

    message queue. */

import java.util.LinkedList;

public class MessageQueueBackend {

  // The two queues

  private MessageQueueImpl leftRightQueue;

  private MessageQueueImpl rightLeftQueue;

  public MessageQueueBackend() {

    LinkedList leftRightPipe = new LinkedList();

    LinkedList rightLeftPipe = new LinkedList();

    leftRightQueue = new MessageQueueImpl(rightLeftPipe, leftRightPipe);

    rightLeftQueue = new MessageQueueImpl(leftRightPipe, rightLeftPipe);

  }

  /** Get one of the two symmetric sides of this message queue. */

  public MessageQueue getFirstQueue() {

    return leftRightQueue;

  }

  /** Get second of the two symmetric sides of this message queue. */

  public MessageQueue getSecondQueue() {

    return rightLeftQueue;

  }

  private class MessageQueueImpl implements MessageQueue {

    private LinkedList readList;

    private LinkedList writeList;

    public MessageQueueImpl(LinkedList listToReadFrom, LinkedList listToWriteTo) {

      readList = listToReadFrom;

      writeList = listToWriteTo;

    }

    public Object readMessage() {

      synchronized(readList) {

        while (readList.isEmpty()) {

          try {

            readList.wait();

          }

          catch (InterruptedException e) {

          }

        }

        return readList.removeFirst();

      }

    }

    public Object readMessageWithTimeout(long millis) {

      synchronized(readList) {

        if (readList.isEmpty()) {

          if (millis == 0) {

            return null;

          }

          try {

            readList.wait(millis);

          }

          catch (InterruptedException e) {

          }

        }

        // If list is still empty after wait, return null

        if (readList.isEmpty()) {

          return null;

        }

        return readList.removeFirst();

      }

    }

    public void writeMessage(Object obj) {

      synchronized(writeList) {

        writeList.addLast(obj);

        writeList.notify();

      }

    }

  }

}