queue.java

OSGI这是一个中间件,与UPNP齐名,是用于移植到嵌入式平台之上

/*
 * Copyright (c) 2003, KNOPFLERFISH project
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following
 * conditions are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 *
 * - Redistributions in binary form must reproduce the above
 *   copyright notice, this list of conditions and the following
 *   disclaimer in the documentation and/or other materials
 *   provided with the distribution.
 *
 * - Neither the name of the KNOPFLERFISH project nor the names of its
 *   contributors may be used to endorse or promote products derived
 *   from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
 * OF THE POSSIBILITY OF SUCH DAMAGE.
 */

package org.knopflerfish.util;

import java.util.Vector;

// ******************** Queue ********************
/**
 * The <code>Queue</code> class represents a first-in-first-out (FIFO) queue
 * of objects.
 * 
 * @author Per Lundgren
 */
public class Queue extends Vector {

    private static final long serialVersionUID = 1L;

    private int m_nMaxSize = -1;

    private boolean queueClosed = false;

    // ==================== Queue ====================
    /**
     * * Constructs an Queue with the specifies maximum size. * *
     * 
     * @param size
     *            maximum queue size.
     */
    public Queue(int size) {
        m_nMaxSize = size;
    }

    // ==================== insert ====================
    /**
     * * Inserts an item into the queue. If there are threads blocked on *
     * <code>remove</code>, one of them is unblocked. * *
     * 
     * @param item
     *            the item to be inserted. *
     * @exception IndexOutOfBoundsException
     *                if maximum queue size is reached.
     */
    public synchronized void insert(Object item)
            throws IndexOutOfBoundsException {
        // Check if queue is full
        if (m_nMaxSize > 0 && size() >= m_nMaxSize)
            throw new IndexOutOfBoundsException("Queue full");

        addElement(item);
        notify();
    }

    // ==================== insertFirst ====================
    /**
     * * Inserts an item first into the queue. If there are threads blocked on *
     * <code>remove</code>, one of them is unblocked. * *
     * 
     * @param item
     *            the item to be inserted.
     */
    public synchronized void insertFirst(Object item) {
        insertElementAt(item, 0);
        notify();
    }

    // ==================== remove ====================
    /**
     * * Removes and returns the first item in the queue. * If the queue is
     * empty, the calling thread will block. * *
     * 
     * @param timeout
     *            timeout in seconds. *
     * @return The first item in the queue, or <code>null</code> if a *
     *         timeout occurred. To distinguish timeouts, <code>null</code> *
     *         items should not be inserted in the queue.
     */
    public synchronized Object removeWait(float timeout) {
        Object obj = null;

        // If queue is empty wait for object to be inserted
        if (isEmpty() && !queueClosed) {
            try {
                if (timeout > 0) {
                    wait(Math.round(timeout * 1000.0f));
                } else
                    wait();
            } catch (InterruptedException e) {
            }
        }

        if (queueClosed) {
            return null;
        }

        try {
            obj = firstElement();
            removeElementAt(0);
        } catch (Exception e) {
        }

        return obj;
    }

    // ==================== remove ====================
    /**
     * * Removes and returns the first object in the queue. * Same as
     * <code>remove(float timeout)</code> but this function * blocks forever. * *
     * 
     * @return The first item in the queue.
     */
    public Object remove() {
        return removeWait(0);
    }

    // ==================== close ====================
    /**
     * * Closes the queue, i.e. wakes up all threads blocking on * a call to
     * remove().
     */

    public synchronized void close() {
        queueClosed = true;
        notifyAll();
    }

}