001/* VMID.java -- The object ID, unique between all virtual machines. 002 Copyright (c) 1996, 1997, 1998, 1999, 2006 Free Software Foundation, Inc. 003 004This file is part of GNU Classpath. 005 006GNU Classpath is free software; you can redistribute it and/or modify 007it under the terms of the GNU General Public License as published by 008the Free Software Foundation; either version 2, or (at your option) 009any later version. 010 011GNU Classpath is distributed in the hope that it will be useful, but 012WITHOUT ANY WARRANTY; without even the implied warranty of 013MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 014General Public License for more details. 015 016You should have received a copy of the GNU General Public License 017along with GNU Classpath; see the file COPYING. If not, write to the 018Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 01902110-1301 USA. 020 021Linking this library statically or dynamically with other modules is 022making a combined work based on this library. Thus, the terms and 023conditions of the GNU General Public License cover the whole 024combination. 025 026As a special exception, the copyright holders of this library give you 027permission to link this library with independent modules to produce an 028executable, regardless of the license terms of these independent 029modules, and to copy and distribute the resulting executable under 030terms of your choice, provided that you also meet, for each linked 031independent module, the terms and conditions of the license of that 032module. An independent module is a module which is not derived from 033or based on this library. If you modify this library, you may extend 034this exception to your version of the library, but you are not 035obligated to do so. If you do not wish to do so, delete this 036exception statement from your version. */ 037 038package java.rmi.dgc; 039 040import gnu.java.lang.CPStringBuilder; 041 042import java.io.Serializable; 043import java.net.InetAddress; 044import java.net.UnknownHostException; 045import java.rmi.server.UID; 046import java.util.Arrays; 047 048/** 049 * An identifier that is unique accross the all virtual machines. This class is 050 * used by distributed garbage collector to identify the virtual machine of 051 * the client, but may also be used in various other cases, when such identifier 052 * is required. This class separately stores and transfers the host IP 053 * address, but will try to do its best also for the case if it failed to 054 * determine it. The alternative algorithms are used in {@link UID} that is 055 * part of this class. The VMID's, created on the same host, but in the two 056 * separately (parallely) running virtual machines are different. 057 */ 058public final class VMID implements Serializable 059{ 060 /** 061 * Use SVUID for interoperability. 062 */ 063 static final long serialVersionUID = -538642295484486218L; 064 065 /** 066 * If true, the IP of this host can ve reliably determined. 067 */ 068 static boolean areWeUnique; 069 070 /** 071 * The IP address of the local host. 072 */ 073 static byte[] localAddr; 074 075 /** 076 * The IP address of the local host. 077 */ 078 private byte[] addr; 079 080 /** 081 * The cached hash code. 082 */ 083 transient int hash; 084 085 /** 086 * The UID of this VMID. 087 */ 088 private UID uid; 089 090 static 091 { 092 // This "local host" value usually indicates that the local 093 // IP address cannot be reliably determined. 094 byte[] localHost = new byte[] { 127, 0, 0, 1 }; 095 096 try 097 { 098 localAddr = InetAddress.getLocalHost().getAddress(); 099 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}