locatorimpl.java

移动Agent编程工具Naplet

/*
 * @<#>Locator.java version 0.1, 7/1/2001
 *
 * 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 Wayne State University. All Rights Reserved.
 */

package naplet.tracing;

import java.rmi.Remote;
import java.rmi.RemoteException;
import naplet.*;
import naplet.server.*;
import naplet.directory.*;

import java.io.*;
import java.net.*;
import java.util.*;

public class LocatorImpl implements Locator { 

      static private int DefaultDelay = 100;
      static private int DefaultTimeOut = 5000;

      private static LocatorImpl instance = null;

      private ServerProperty property;

      protected LocatorImpl(ServerProperty property) {
	 this.property = property;
      }

      public static LocatorImpl getInstance(ServerProperty property) {
	 if (instance==null)
	    instance = new LocatorImpl(property);
	 return instance;
      }

      public void update( NapletID id, URN server ) {};

      public URN lookup( NapletID nid ) 
	 throws NapletLocateException {
	 return lookup( nid, DefaultTimeOut );
      }
      /**
       * Look up naplet server
       *
       * @param nid Naplet id 
       * @param timeout Time limit to locate a naplet
       */
      public URN lookup( NapletID nid, long timeout ) 
	 throws NapletLocateException {
		
	 int delay = DefaultDelay;
	 URN server = null; 
		
	 NapletDirectory directory = property.getNapletDirectory();

	 boolean stop = false;
	 long begin = System.currentTimeMillis();

	 if (directory==null) {
	    throw new NapletLocateException(
	       "Cann't locate the naplet without naplet Directory");
	 } else {
	    while ( !stop ) {
	       System.out.println("Try to locate Naplet server");

	       try {
		  server = directory.lookup( nid );
		  stop = true;
	       } catch (DirectoryAccessException dae) {
		  long end = System.currentTimeMillis();
		  if (end-begin<timeout) {
		     try {
			Thread.sleep(delay<<1);
		     } catch (InterruptedException ie) { 
			stop = true; 
		     }
		  } else {
		     stop = true;
		  }
	       } catch (java.rmi.RemoteException re) {
		  throw new NapletLocateException(
		     "Cann't locate the naplet");
	       }
	    }	
	 }	
	 return server;
      }
}