closablefifoqueue.java

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//
// This file is part of the OpenNMS(R) Application.
//
// OpenNMS(R) is Copyright (C) 2002-2003 The OpenNMS Group, Inc.  All rights reserved.
// OpenNMS(R) is a derivative work, containing both original code, included code and modified
// code that was published under the GNU General Public License. Copyrights for modified 
// and included code are below.
//
// OpenNMS(R) is a registered trademark of The OpenNMS Group, Inc.
// 
// Copyright (C) 1999-2001 Oculan Corp.  All rights reserved.
//
// This program is free software; you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation; either version 2 of the License, or
// (at your option) any later version.
//
// This program 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 for more details.
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// along with this program; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
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//      OpenNMS Licensing       <[e-mail]>
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package org.opennms.core.queue;

/**
 * <p>
 * This interface defines a FIFO queue that can be open and closed to control
 * the addition of elements to the queue. When the queue is opened it is
 * possible to add new elements to the queue. When the queue is closed, it is
 * should not be possible to add elements to the queue. It should always be
 * possible to read elements from the queue, so long as it is not empty.
 * </p>
 * 
 * @author <a href="mailto:[e-mail]">Brian Weaver </a>
 * @author <a href="http://www.opennms.org/">OpenNMS </a>
 * 
 */
public interface ClosableFifoQueue extends FifoQueue {
    /**
     * Returns true if the queue is currently open.
     * 
     * @return True if the queue is open.
     */
    public boolean isOpen();

    /**
     * Returns true if the queue is currently closed.
     * 
     * @return True if the queue is closed.
     */
    public boolean isClosed();

    /**
     * Closes a currently open queue. When a queue is closed is should still
     * allow elements already in the queue to be removed, but new elements
     * should not be added.
     * 
     * @exception org.opennms.core.queue.FifoQueueException
     *                Thrown if an error occurs closing the queue.
     */
    public void close() throws FifoQueueException;

    /**
     * Ensures that the queue is open and new elements can be added to the
     * queue.
     * 
     * @exception org.opennms.core.queue.FifoQueueException
     *                Thrown if an error occurs opening the queue.
     */
    public void open() throws FifoQueueException;
}