queue.java.svn-base

网络模拟器

package jns.element;


/**
 Queue implements a queue that can be attached to an interface.
 */
public abstract class Queue extends Element
{

    protected Interface m_iface;
    protected int m_maxlength;
    protected int m_curlength;

    /**
     Create a new queue with the given maximum length (in bytes!).
     @param length maximum length of the queue in bytes, 0 if the queue is
     infinite
     */
    public Queue(int length)
    {
        m_maxlength = length;
        m_curlength = 0;
        m_iface = null;
    }


    public void attach(Interface iface)
    {
        m_iface = iface;
    }

    /**
     Return the maximum length of the queue in bytes. Returns 0 for an
     infinite queue.
     @return the maximum queue length in bytes. 0 if the queue is infinite
     */
    public int getMaximumLength()
    {
        return m_maxlength;
    }

    /**
     Check if the queue is full if a given number of bytes is to be added.
     @param bytes the number of bytes to be added
     @return true if the number of bytes could be added, false otherwise
     */
    public boolean isFull(int bytes)
    {
        if(m_maxlength == 0) return false;
        return m_curlength + bytes >= m_maxlength;
    }

    public boolean isEmpty()
    {
        return m_curlength == 0;
    }

    /**
     Enqueue a packet in this queue, if it fits in. The routine fails
     silently if the packet does not fit it. If you have to know in advance
     if it will, use the isFull function first.
     @param packet the packet to enqueue
     @see isFull
     */
    public abstract void enqueue(IPPacket packet);


    /**
     Dequeue a packet from this queue. Note that this does not mean the
     packet at the end of the queue is being dequeued. The queueing policy
     is decided by subclasses.
     @return a dequeued packet that was removed from the queue
     */
    public abstract IPPacket dequeue();

}