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/* * @(#)VMID.java 1.21 05/11/17 * * Copyright 2006 Sun Microsystems, Inc. All rights reserved. * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms. */ package java.rmi.dgc; import java.io.*; import java.net.*; import java.rmi.server.UID; import java.security.*; /** * A VMID is a identifier that is unique across all Java virtual * machines. VMIDs are used by the distributed garbage collector * to identify client VMs. * * @version 1.21, 11/17/05 * @author Ann Wollrath * @author Peter Jones */ public final class VMID implements java.io.Serializable { /** array of bytes uniquely identifying this host */ private static byte[] localAddr = computeAddressHash(); /** * @serial array of bytes uniquely identifying host created on */ private byte[] addr; /** * @serial unique identifier with respect to host created on */ private UID uid; /** indicate compatibility with JDK 1.1.x version of class */ private static final long serialVersionUID = -538642295484486218L; /** * Create a new VMID. Each new VMID returned from this constructor * is unique for all Java virtual machines under the following * conditions: a) the conditions for uniqueness for objects of * the class <code>java.rmi.server.UID</code> are satisfied, and b) an * address can be obtained for this host that is unique and constant * for the lifetime of this object. <p> */ public VMID() { addr = localAddr; uid = new UID(); } /** * Return true if an accurate address can be determined for this * host. If false, reliable VMID cannot be generated from this host * @return true if host address can be determined, false otherwise * @deprecated */ @Deprecated public static boolean isUnique() { return true; } /** * Compute hash code for this VMID. */ public int hashCode() { return uid.hashCode(); } /** * Compare this VMID to another, and return true if they are the * same identifier. */ public boolean equals(Object obj) { if (obj instanceof VMID) { VMID vmid = (VMID) obj; if (!uid.equals(vmid.uid)) return false; if ((addr == null) ^ (vmid.addr == null)) return false; if (addr != null) { if (addr.length != vmid.addr.length) return false; for (int i = 0; i < addr.length; ++ i) if (addr[i] != vmid.addr[i]) return false; } return true; } else { return false; } } /** * Return string representation of this VMID. */ public String toString() { StringBuffer result = new StringBuffer(); if (addr != null) for (int i = 0; i < addr.length; ++ i) { int x = (int) (addr[i] & 0xFF); result.append((x < 0x10 ? "0" : "") + Integer.toString(x, 16)); } result.append(':'); result.append(uid.toString()); return result.toString(); } /** * Compute the hash an IP address. The hash is the first 8 bytes * of the SHA digest of the IP address. */ private static byte[] computeAddressHash() { /* * Get the local host's IP address. */ byte[] addr = (byte[]) java.security.AccessController.doPrivileged( new PrivilegedAction() { public Object run() { try { return InetAddress.getLocalHost().getAddress(); } catch (Exception e) { } return new byte[] { 0, 0, 0, 0 }; } }); byte[] addrHash; final int ADDR_HASH_LENGTH = 8; try { /* * Calculate message digest of IP address using SHA. */ MessageDigest md = MessageDigest.getInstance("SHA"); ByteArrayOutputStream sink = new ByteArrayOutputStream(64); DataOutputStream out = new DataOutputStream( new DigestOutputStream(sink, md)); out.write(addr, 0, addr.length); out.flush(); byte digest[] = md.digest(); int hashlength = Math.min(ADDR_HASH_LENGTH, digest.length); addrHash = new byte[hashlength]; System.arraycopy(digest, 0, addrHash, 0, hashlength); } catch (IOException ignore) { /* can't happen, but be deterministic anyway. */ addrHash = new byte[0]; } catch (NoSuchAlgorithmException complain) { throw new InternalError(complain.toString()); } return addrHash; } }