libjava/classpath/java/rmi/dgc/VMID.java

   1 /* VMID.java -- The object ID, unique between all virtual machines.
   2    Copyright (c) 1996, 1997, 1998, 1999, 2006 Free Software Foundation, Inc.
   3
   4 This file is part of GNU Classpath.
   5
   6 GNU Classpath is free software; you can redistribute it and/or modify
   7 it under the terms of the GNU General Public License as published by
   8 the Free Software Foundation; either version 2, or (at your option)
   9 any later version.
  10
  11 GNU Classpath is distributed in the hope that it will be useful, but
  12 WITHOUT ANY WARRANTY; without even the implied warranty of
  13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14 General Public License for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with GNU Classpath; see the file COPYING.  If not, write to the
  18 Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
  19 02110-1301 USA.
  20
  21 Linking this library statically or dynamically with other modules is
  22 making a combined work based on this library.  Thus, the terms and
  23 conditions of the GNU General Public License cover the whole
  24 combination.
  25
  26 As a special exception, the copyright holders of this library give you
  27 permission to link this library with independent modules to produce an
  28 executable, regardless of the license terms of these independent
  29 modules, and to copy and distribute the resulting executable under
  30 terms of your choice, provided that you also meet, for each linked
  31 independent module, the terms and conditions of the license of that
  32 module.  An independent module is a module which is not derived from
  33 or based on this library.  If you modify this library, you may extend
  34 this exception to your version of the library, but you are not
  35 obligated to do so.  If you do not wish to do so, delete this
  36 exception statement from your version. */
  37
  38 package java.rmi.dgc;
  39
  40 import gnu.java.lang.CPStringBuilder;
  41
  42 import java.io.Serializable;
  43 import java.net.InetAddress;
  44 import java.net.UnknownHostException;
  45 import java.rmi.server.UID;
  46 import java.util.Arrays;
  47
  48 /**
  49  * An identifier that is unique accross the all virtual machines. This class is
  50  * used by distributed garbage collector to identify the virtual machine of
  51  * the client, but may also be used in various other cases, when such identifier
  52  * is required. This class separately stores and transfers the host IP
  53  * address, but will try to do its best also for the case if it failed to
  54  * determine it. The alternative algorithms are used in {@link UID} that is
  55  * part of this class. The VMID's, created on the same host, but in the two
  56  * separately (parallely) running virtual machines are different.
  57  */
  58 public final class VMID implements Serializable
  59 {
  60   /**
  61    * Use SVUID for interoperability.
  62    */
  63   static final long serialVersionUID = -538642295484486218L;
  64
  65   /**
  66    * If true, the IP of this host can ve reliably determined.
  67    */
  68   static boolean areWeUnique;
  69
  70   /**
  71    * The IP address of the local host.
  72    */
  73   static byte[] localAddr;
  74
  75   /**
  76    * The IP address of the local host.
  77    */
  78   private byte[] addr;
  79
  80   /**
  81    * The cached hash code.
  82    */
  83   transient int hash;
  84
  85   /**
  86    * The UID of this VMID.
  87    */
  88   private UID uid;
  89
  90   static
  91     {
  92       // This "local host" value usually indicates that the local
  93       // IP address cannot be reliably determined.
  94       byte[] localHost = new byte[] { 127, 0, 0, 1 };
  95
  96       try
  97         {
  98           localAddr = InetAddress.getLocalHost().getAddress();
  99           areWeUnique = !Arrays.equals(localHost, localAddr);
 100         }
 101       catch (UnknownHostException uhex)
 102         {
 103           localAddr = localHost;
 104           areWeUnique = false;
 105         }
 106     }
 107
 108   /**
 109    * Create the new VMID. All VMID's are unique accross tha all virtual
 110    * machines.
 111    */
 112   public VMID()
 113   {
 114     addr = localAddr;
 115     uid = new UID();
 116   }
 117
 118   /**
 119    * Return true if it is possible to get the accurate address of this host.
 120    * If false is returned, the created VMID's are less reliable, but the
 121    * starting time and possibly the memory allocation are also taken into
 122    * consideration in the incorporated UID. Hence the VMID's, created on the
 123    * different virtual machines, still should be different.
 124    *
 125    * @deprecated VMID's are more or less always reliable.
 126    *
 127    * @return false if the local host ip address is 127.0.0.1 or unknown,
 128    * true otherwise.
 129    */
 130   public static boolean isUnique ()
 131   {
 132     return areWeUnique;
 133   }
 134
 135   /**
 136    * Get the hash code of this VMID.
 137    */
 138   public int hashCode ()
 139   {
 140     if (hash==0)
 141       {
 142         for (int i = 0; i < localAddr.length; i++)
 143             hash += addr[i];
 144         hash = hash ^ uid.hashCode();
 145       }
 146     return hash;
 147   }
 148
 149   /**
 150    * Returns true if the passed parameter is also VMID and it is equal to this
 151    * VMID. The VMID should only be equal to itself (also if the passed value is
 152    * another instance, cloned by serialization).
 153    */
 154   public boolean equals(Object obj)
 155   {
 156     if (obj instanceof VMID)
 157       {
 158         VMID other = (VMID) obj;
 159
 160         // The UID's are compared faster than arrays.
 161         return uid.equals(other.uid) && Arrays.equals(addr, other.addr);
 162       }
 163     else
 164       return false;
 165
 166   }
 167
 168   /**
 169    * Get the string representation of this VMID.
 170    */
 171   public String toString ()
 172   {
 173     CPStringBuilder buf = new CPStringBuilder ("[VMID: ");
 174
 175     for (int i = 0; i < addr.length; i++)
 176       {
 177         if (i > 0)
 178           {
 179             buf.append (".");
 180           }
 181
 182         buf.append (Integer.toString (addr [i]));
 183       }
 184
 185     buf.append (" ");
 186     buf.append (uid.toString ());
 187     buf.append ("]");
 188
 189     return buf.toString();
 190   }
 191 }