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