1/* 2 * Copyright (c) 1996, 2013, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. Oracle designates this 8 * particular file as subject to the "Classpath" exception as provided 9 * by Oracle in the LICENSE file that accompanied this code. 10 * 11 * This code is distributed in the hope that it will be useful, but WITHOUT 12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 14 * version 2 for more details (a copy is included in the LICENSE file that 15 * accompanied this code). 16 * 17 * You should have received a copy of the GNU General Public License version 18 * 2 along with this work; if not, write to the Free Software Foundation, 19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 20 * 21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 22 * or visit www.oracle.com if you need additional information or have any 23 * questions. 24 */ 25 26package java.rmi.dgc; 27 28import java.rmi.server.UID; 29import java.security.SecureRandom; 30 31/** 32 * A VMID is a identifier that is unique across all Java virtual 33 * machines. VMIDs are used by the distributed garbage collector 34 * to identify client VMs. 35 * 36 * @author Ann Wollrath 37 * @author Peter Jones 38 */ 39public final class VMID implements java.io.Serializable { 40 /** Array of bytes uniquely identifying this host */ 41 private static final byte[] randomBytes; 42 43 /** 44 * @serial array of bytes uniquely identifying host created on 45 */ 46 private byte[] addr; 47 48 /** 49 * @serial unique identifier with respect to host created on 50 */ 51 private UID uid; 52 53 /** indicate compatibility with JDK 1.1.x version of class */ 54 private static final long serialVersionUID = -538642295484486218L; 55 56 static { 57 // Generate 8 bytes of random data. 58 SecureRandom secureRandom = new SecureRandom(); 59 byte bytes[] = new byte[8]; 60 secureRandom.nextBytes(bytes); 61 randomBytes = bytes; 62 } 63 64 /** 65 * Create a new VMID. Each new VMID returned from this constructor 66 * is unique for all Java virtual machines under the following 67 * conditions: a) the conditions for uniqueness for objects of 68 * the class <code>java.rmi.server.UID</code> are satisfied, and b) an 69 * address can be obtained for this host that is unique and constant 70 * for the lifetime of this object. 71 */ 72 public VMID() { 73 addr = randomBytes; 74 uid = new UID(); 75 } 76 77 /** 78 * Return true if an accurate address can be determined for this 79 * host. If false, reliable VMID cannot be generated from this host 80 * @return true if host address can be determined, false otherwise 81 * @deprecated 82 */ 83 @Deprecated 84 public static boolean isUnique() { 85 return true; 86 } 87 88 /** 89 * Compute hash code for this VMID. 90 */ 91 public int hashCode() { 92 return uid.hashCode(); 93 } 94 95 /** 96 * Compare this VMID to another, and return true if they are the 97 * same identifier. 98 */ 99 public boolean equals(Object obj) { 100 if (obj instanceof VMID) { 101 VMID vmid = (VMID) obj; 102 if (!uid.equals(vmid.uid)) 103 return false; 104 if ((addr == null) ^ (vmid.addr == null)) 105 return false; 106 if (addr != null) { 107 if (addr.length != vmid.addr.length) 108 return false; 109 for (int i = 0; i < addr.length; ++ i) 110 if (addr[i] != vmid.addr[i]) 111 return false; 112 } 113 return true; 114 } else { 115 return false; 116 } 117 } 118 119 /** 120 * Return string representation of this VMID. 121 */ 122 public String toString() { 123 StringBuilder sb = new StringBuilder(); 124 if (addr != null) 125 for (int i = 0; i < addr.length; ++ i) { 126 int x = addr[i] & 0xFF; 127 sb.append((x < 0x10 ? "0" : "") + 128 Integer.toString(x, 16)); 129 } 130 sb.append(':'); 131 sb.append(uid.toString()); 132 return sb.toString(); 133 } 134} 135