Source for java.rmi.server.UID

   1: /* UID.java -- The unique object Id
   2:    Copyright (c) 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: 
  39: package java.rmi.server;
  40: 
  41: import java.io.DataInput;
  42: import java.io.DataOutput;
  43: import java.io.IOException;
  44: import java.io.Serializable;
  45: import java.net.InetAddress;
  46: 
  47: /**
  48:  * Represents the unique identifier over time for the host which has generated
  49:  * it. It contains time (when created), counter (the number of the UID
  50:  * creation order) and virtual machine id components. The UID can also be
  51:  * constructed specifying a "well known" identifier in the for of short:
  52:  * this identifier defines the UID uniqueness alone.
  53:  *
  54:  * @author Audrius Meskauskas (audriusa@bioinformatics.org)
  55:  */
  56: public final class UID
  57:     implements Serializable
  58: {
  59:   /**
  60:    * Use the serial version uid for interoperability.
  61:    */
  62:   private static final long serialVersionUID = 1086053664494604050L;
  63: 
  64:   /**
  65:    * The UID counter (the ordinary number in the sequence of number of UID's,
  66:    * created during the recent millisecond). In the next millisecond, it
  67:    * starts from the minimal value again. In the unlikely case of creating
  68:    * more than 65536 uids per millisecond the process pauses till the next
  69:    * ms.
  70:    */
  71:   private static short uidCounter = Short.MIN_VALUE;
  72: 
  73:   /**
  74:    * The time, when the last UID has been created.
  75:    */
  76:   private static long last;
  77: 
  78:   /**
  79:    * This constant tries to be the unique identifier of the virtual machine.
  80:    */
  81:   private static final int machineId = getMachineId();
  82: 
  83:   /**
  84:    * The UID number in the UID creation sequence.
  85:    */
  86:   private short count;
  87: 
  88:   /**
  89:    * Always gets the uniqueNr value.
  90:    */
  91:   private int unique;
  92: 
  93:   /**
  94:    * The time stamp, when the UID was created.
  95:    */
  96:   private long time;
  97: 
  98:   /**
  99:    * Create the new UID that would have the described features of the
 100:    * uniqueness.
 101:    */
 102:   public UID()
 103:   {
 104:     synchronized (UID.class)
 105:       {
 106:         time = System.currentTimeMillis();
 107:         unique = machineId;
 108:         if (time > last)
 109:           {
 110:             last = time;
 111:             count = uidCounter = Short.MIN_VALUE;
 112:           }
 113:         else
 114:           {
 115:             if (uidCounter == Short.MAX_VALUE)
 116:               {
 117:                 // Make a 2 ms pause if the counter has reached the maximal
 118:                 // value. This should seldom happen.
 119:                 try
 120:                   {
 121:                     Thread.sleep(2);
 122:                   }
 123:                 catch (InterruptedException e)
 124:                   {
 125:                   }
 126:                 uidCounter = Short.MIN_VALUE;
 127:                 time = last = System.currentTimeMillis();
 128:               }
 129:             count = ++uidCounter;
 130:           }
 131:       }
 132:   }
 133: 
 134:   /**
 135:    * Create the new UID with the well known id (number). All UIDs, creates
 136:    * with the this constructor having the same parameter are equal to each
 137:    * other (regardless to the host and time where they were created.
 138:    *
 139:    * @param wellKnownId the well known UID.
 140:    */
 141:   public UID(short wellKnownId)
 142:   {
 143:     unique = wellKnownId;
 144:   }
 145: 
 146:   /**
 147:    * Get the hashCode of this UID.
 148:    */
 149:   public int hashCode()
 150:   {
 151:     return (int) (unique ^ time ^ count);
 152:   }
 153: 
 154:   /**
 155:    * Compare this UID with another UID for equality (not equal to other types of
 156:    * objects).
 157:    */
 158:   public boolean equals(Object other)
 159:   {
 160:     if (other instanceof UID)
 161:       {
 162:         UID ui = (UID) other;
 163:         return unique == ui.unique && time == ui.time && count == ui.count;
 164:       }
 165:     else
 166:       return false;
 167:   }
 168: 
 169:   public static UID read(DataInput in) throws IOException
 170:   {
 171:     UID uid = new UID();
 172:     uid.unique = in.readInt();
 173:     uid.time = in.readLong();
 174:     uid.count = in.readShort();
 175:     return (uid);
 176:   }
 177: 
 178:   public void write(DataOutput out) throws IOException
 179:   {
 180:     out.writeInt(unique);
 181:     out.writeLong(time);
 182:     out.writeShort(count);
 183:   }
 184: 
 185:   /**
 186:    * Do our best to get the Id of this virtual machine.
 187:    */
 188:   static int getMachineId()
 189:   {
 190:     int hostIpHash;
 191: 
 192:     try
 193:       {
 194:         // Try to get the host IP.
 195:         String host = InetAddress.getLocalHost().toString();
 196:         // This hash is content - based, not the address based.
 197:         hostIpHash = host.hashCode();
 198:       }
 199:     catch (Exception e)
 200:       {
 201:         // Failed due some reason.
 202:         hostIpHash = 0;
 203:       }
 204: 
 205:     // Should be the unque address if hashcodes are addresses.
 206:     // Additionally, add the time when the RMI system was probably started
 207:     // (this class was first instantiated).
 208:     return new Object().hashCode() ^ (int) System.currentTimeMillis()
 209:            ^ hostIpHash;
 210:   }
 211: 
 212:     /**
 213:    * Get the string representation of this UID.
 214:    *
 215:    * @return a string, uniquely identifying this id.
 216:    */
 217:   public String toString()
 218:   {
 219:     int max = Character.MAX_RADIX;
 220:     // Translate into object count, counting from 0.
 221:     long lc = (count - Short.MIN_VALUE) & 0xFFFF;
 222:     return Long.toString(unique, max) + ":" + Long.toString(time, max) + "."
 223:            + Long.toString(lc, max);
 224:   }
 225: }