001    /* VMID.java -- The object ID, unique between all virtual machines.
002       Copyright (c) 1996, 1997, 1998, 1999, 2006 Free Software Foundation, Inc.
003    
004    This file is part of GNU Classpath.
005    
006    GNU Classpath is free software; you can redistribute it and/or modify
007    it under the terms of the GNU General Public License as published by
008    the Free Software Foundation; either version 2, or (at your option)
009    any later version.
010     
011    GNU Classpath is distributed in the hope that it will be useful, but
012    WITHOUT ANY WARRANTY; without even the implied warranty of
013    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
014    General Public License for more details.
015    
016    You should have received a copy of the GNU General Public License
017    along with GNU Classpath; see the file COPYING.  If not, write to the
018    Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
019    02110-1301 USA.
020    
021    Linking this library statically or dynamically with other modules is
022    making a combined work based on this library.  Thus, the terms and
023    conditions of the GNU General Public License cover the whole
024    combination.
025    
026    As a special exception, the copyright holders of this library give you
027    permission to link this library with independent modules to produce an
028    executable, regardless of the license terms of these independent
029    modules, and to copy and distribute the resulting executable under
030    terms of your choice, provided that you also meet, for each linked
031    independent module, the terms and conditions of the license of that
032    module.  An independent module is a module which is not derived from
033    or based on this library.  If you modify this library, you may extend
034    this exception to your version of the library, but you are not
035    obligated to do so.  If you do not wish to do so, delete this
036    exception statement from your version. */
037    
038    package java.rmi.dgc;
039    
040    import java.io.Serializable;
041    import java.net.InetAddress;
042    import java.net.UnknownHostException;
043    import java.rmi.server.UID;
044    import java.util.Arrays;
045    
046    /**
047     * An identifier that is unique accross the all virtual machines. This class is
048     * used by distributed garbage collector to identify the virtual machine of
049     * the client, but may also be used in various other cases, when such identifier
050     * is required. This class separately stores and transfers the host IP 
051     * address, but will try to do its best also for the case if it failed to
052     * determine it. The alternative algorithms are used in {@link UID} that is 
053     * part of this class. The VMID's, created on the same host, but in the two
054     * separately (parallely) running virtual machines are different.
055     */
056    public final class VMID implements Serializable
057    {
058      /**
059       * Use SVUID for interoperability.
060       */
061      static final long serialVersionUID = -538642295484486218L;
062      
063      /**
064       * If true, the IP of this host can ve reliably determined.
065       */
066      static boolean areWeUnique;
067      
068      /**
069       * The IP address of the local host.
070       */
071      static byte[] localAddr;
072    
073      /**
074       * The IP address of the local host.
075       */
076      private byte[] addr;
077      
078      /**
079       * The cached hash code.
080       */
081      transient int hash;
082      
083      /**
084       * The UID of this VMID.
085       */
086      private UID uid;
087    
088      static
089        {
090          // This "local host" value usually indicates that the local 
091          // IP address cannot be reliably determined.
092          byte[] localHost = new byte[] { 127, 0, 0, 1 };
093    
094          try
095            {
096              localAddr = InetAddress.getLocalHost().getAddress();
097              areWeUnique = !Arrays.equals(localHost, localAddr);
098            }
099          catch (UnknownHostException uhex)
100            {
101              localAddr = localHost;
102              areWeUnique = false;
103            }
104        }
105      
106      /**
107       * Create the new VMID. All VMID's are unique accross tha all virtual
108       * machines. 
109       */
110      public VMID()
111      {
112        addr = localAddr;
113        uid = new UID();
114      }
115    
116      /**
117       * Return true if it is possible to get the accurate address of this host.
118       * If false is returned, the created VMID's are less reliable, but the
119       * starting time and possibly the memory allocation are also taken into
120       * consideration in the incorporated UID. Hence the VMID's, created on the 
121       * different virtual machines, still should be different.
122       * 
123       * @deprecated VMID's are more or less always reliable.
124       * 
125       * @return false if the local host ip address is 127.0.0.1 or unknown,
126       * true otherwise.
127       */
128      public static boolean isUnique ()
129      {
130        return areWeUnique;
131      }
132      
133      /**
134       * Get the hash code of this VMID.
135       */
136      public int hashCode ()
137      {
138        if (hash==0)
139          {
140            for (int i = 0; i < localAddr.length; i++)
141                hash += addr[i];
142            hash = hash ^ uid.hashCode();
143          }
144        return hash;
145      }
146      
147      /**
148       * Returns true if the passed parameter is also VMID and it is equal to this
149       * VMID. The VMID should only be equal to itself (also if the passed value is
150       * another instance, cloned by serialization).
151       */
152      public boolean equals(Object obj)
153      {
154        if (obj instanceof VMID)
155          {
156            VMID other = (VMID) obj;
157    
158            // The UID's are compared faster than arrays.
159            return uid.equals(other.uid) && Arrays.equals(addr, other.addr);
160          }
161        else
162          return false;
163    
164      }
165      
166      /**
167       * Get the string representation of this VMID.
168       */
169      public String toString ()
170      {
171        StringBuffer buf = new StringBuffer ("[VMID: ");
172        
173        for (int i = 0; i < addr.length; i++)
174          {
175            if (i > 0)
176              {
177                buf.append (".");
178              }
179            
180            buf.append (Integer.toString (addr [i]));
181          }
182        
183        buf.append (" ");
184        buf.append (uid.toString ());
185        buf.append ("]");
186    
187        return buf.toString();
188      }
189    }