mailboximpl.java

移动Agent编程工具Naplet

/*
 * @<#>MailBoxImpl.java version 0.0.1, 1/1/2000
 *
 * THIS PROGRAM IS FREE SOFTWARE; YOU CAN DISTRIBUTE IT AND/OR
 * MODIFY IT UNDER THE TERMS OF THE GNU GENERAL PUBLIC LICENSE 
 * AS PUBLISHED BY THE FREE SOFTWARE FOUNDATION.
 *
 * 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.
 *
 * Copyright (c) 2000 Cheng-Zhong Xu. All Rights Reserved.
 */
package naplet.message;

import java.rmi.RemoteException;
import java.util.*;
import java.io.*;
import naplet.*;

/**
 * The <code>MailBoxImpl</code> class implements <code>MailBox</code>
 * interface. Each long lived naplet is assigned to a mailbox once it
 * arrives at a server.
 *
 * @see MailBox
 * @version 0.0.1
 * @author C. Xu
 */

public class MailBoxImpl implements MailBox {

	private boolean newMailFlag = false;		// New Mail
	private Vector mailbox;

	int mboxSize;

	/**
	 * Constructs a mailbox
	 * @param size initial size of the mailbox. By default, it is 10
	 */
	public MailBoxImpl(int size) {
		if (size>0) {
			mailbox = new Vector(size); 
			mboxSize = size;
		} else {
			mailbox = new Vector( DefaultMailBoxSize );
			mboxSize = DefaultMailBoxSize;
		}
	}

	/**
	 * Constructs a mailbox
	 * By default, the initial mailbox size is 10. 
	 */
	public MailBoxImpl() {
		mboxSize = DefaultMailBoxSize;
		mailbox = new Vector( DefaultMailBoxSize );
	}

	/**
	 * Insert a message into a mailbox. 
	 */
	public synchronized void putMessage( Message msg ) 
			throws InterruptedException
	{
		while ( mailbox.size() == mboxSize )
			wait();

		mailbox.addElement( msg );
		newMailFlag =  true;
		notify();
	}

	/**
	 * Fetch and remove the first mail from mailbox
	 */
	public synchronized Message getMessage()  
			throws InterruptedException {

		while ( mailbox.isEmpty() )
			wait();

		Message msg = (Message) mailbox.firstElement();
		mailbox.removeElement( msg );
		notify();
		newMailFlag = false;
		return msg;	
	}


	/**
	 * Try to get a mail for mailbox
	 */
	public synchronized Message tryGetMessage()
	{
		Message msg = null;
		if ( ! mailbox.isEmpty() ) {
			msg = (Message) mailbox.firstElement();
			mailbox.removeElement( msg );
			notify();
			newMailFlag = false;
		}
		return msg;	
	}

	/**
	 * Try to get a mail from a specific sender 
	 */
	public synchronized Message tryGetMessage(NapletID nid)
	{
		Message msg = null;
		boolean going = true;
		if ( going && !mailbox.isEmpty() ) {
			Enumeration enum = mailbox.elements();

			while ( !enum.hasMoreElements() ) {
				Message m = (Message) enum.nextElement();
				NapletID sid = m.getSender();
				if ( nid.equals( sid ) ) {
					msg = m; 
					mailbox.removeElement( msg );
					notify();

					going = false;
				}
			}	
			newMailFlag = false;
		}
		return msg;
	}
		
	public synchronized void clearMailBox() {
		if ( !mailbox.isEmpty() ) {
			mailbox.removeAllElements();	
			newMailFlag = false;
		}
	}

	public synchronized boolean checkMailBox() {
		boolean flag = newMailFlag;
		newMailFlag = false;
		return flag;
	}
}