| /* UID.java -- The unique object Id |
| Copyright (c) 2006 Free Software Foundation, Inc. |
| |
| This file is part of GNU Classpath. |
| |
| GNU Classpath is free software; you can redistribute it and/or modify |
| it under the terms of the GNU General Public License as published by |
| the Free Software Foundation; either version 2, or (at your option) |
| any later version. |
| |
| GNU Classpath is distributed in the hope that it will be useful, but |
| WITHOUT ANY WARRANTY; without even the implied warranty of |
| MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
| General Public License for more details. |
| |
| You should have received a copy of the GNU General Public License |
| along with GNU Classpath; see the file COPYING. If not, write to the |
| Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA |
| 02110-1301 USA. |
| |
| Linking this library statically or dynamically with other modules is |
| making a combined work based on this library. Thus, the terms and |
| conditions of the GNU General Public License cover the whole |
| combination. |
| |
| As a special exception, the copyright holders of this library give you |
| permission to link this library with independent modules to produce an |
| executable, regardless of the license terms of these independent |
| modules, and to copy and distribute the resulting executable under |
| terms of your choice, provided that you also meet, for each linked |
| independent module, the terms and conditions of the license of that |
| module. An independent module is a module which is not derived from |
| or based on this library. If you modify this library, you may extend |
| this exception to your version of the library, but you are not |
| obligated to do so. If you do not wish to do so, delete this |
| exception statement from your version. */ |
| |
| |
| package java.rmi.server; |
| |
| import java.io.DataInput; |
| import java.io.DataOutput; |
| import java.io.IOException; |
| import java.io.Serializable; |
| import java.net.InetAddress; |
| |
| /** |
| * Represents the unique identifier over time for the host which has generated |
| * it. It contains time (when created), counter (the number of the UID |
| * creation order) and virtual machine id components. The UID can also be |
| * constructed specifying a "well known" identifier in the for of short: |
| * this identifier defines the UID uniqueness alone. |
| * |
| * @author Audrius Meskauskas (audriusa@bioinformatics.org) |
| */ |
| public final class UID |
| implements Serializable |
| { |
| /** |
| * Use the serial version uid for interoperability. |
| */ |
| private static final long serialVersionUID = 1086053664494604050L; |
| |
| /** |
| * The UID counter (the ordinary number in the sequence of number of UID's, |
| * created during the recent millisecond). In the next millisecond, it |
| * starts from the minimal value again. In the unlikely case of creating |
| * more than 65536 uids per millisecond the process pauses till the next |
| * ms. |
| */ |
| private static short uidCounter = Short.MIN_VALUE; |
| |
| /** |
| * The time, when the last UID has been created. |
| */ |
| private static long last; |
| |
| /** |
| * This constant tries to be the unique identifier of the virtual machine. |
| */ |
| private static final int machineId = getMachineId(); |
| |
| /** |
| * The UID number in the UID creation sequence. |
| */ |
| private short count; |
| |
| /** |
| * Always gets the uniqueNr value. |
| */ |
| private int unique; |
| |
| /** |
| * The time stamp, when the UID was created. |
| */ |
| private long time; |
| |
| /** |
| * Create the new UID that would have the described features of the |
| * uniqueness. |
| */ |
| public UID() |
| { |
| synchronized (UID.class) |
| { |
| time = System.currentTimeMillis(); |
| unique = machineId; |
| if (time > last) |
| { |
| last = time; |
| count = uidCounter = Short.MIN_VALUE; |
| } |
| else |
| { |
| if (uidCounter == Short.MAX_VALUE) |
| { |
| // Make a 2 ms pause if the counter has reached the maximal |
| // value. This should seldom happen. |
| try |
| { |
| Thread.sleep(2); |
| } |
| catch (InterruptedException e) |
| { |
| } |
| uidCounter = Short.MIN_VALUE; |
| time = last = System.currentTimeMillis(); |
| } |
| count = ++uidCounter; |
| } |
| } |
| } |
| |
| /** |
| * Create the new UID with the well known id (number). All UIDs, creates |
| * with the this constructor having the same parameter are equal to each |
| * other (regardless to the host and time where they were created. |
| * |
| * @param wellKnownId the well known UID. |
| */ |
| public UID(short wellKnownId) |
| { |
| unique = wellKnownId; |
| } |
| |
| /** |
| * Get the hashCode of this UID. |
| */ |
| public int hashCode() |
| { |
| return (int) (unique ^ time ^ count); |
| } |
| |
| /** |
| * Compare this UID with another UID for equality (not equal to other types of |
| * objects). |
| */ |
| public boolean equals(Object other) |
| { |
| if (other instanceof UID) |
| { |
| UID ui = (UID) other; |
| return unique == ui.unique && time == ui.time && count == ui.count; |
| } |
| else |
| return false; |
| } |
| |
| public static UID read(DataInput in) throws IOException |
| { |
| UID uid = new UID(); |
| uid.unique = in.readInt(); |
| uid.time = in.readLong(); |
| uid.count = in.readShort(); |
| return (uid); |
| } |
| |
| public void write(DataOutput out) throws IOException |
| { |
| out.writeInt(unique); |
| out.writeLong(time); |
| out.writeShort(count); |
| } |
| |
| /** |
| * Do our best to get the Id of this virtual machine. |
| */ |
| static int getMachineId() |
| { |
| int hostIpHash; |
| |
| try |
| { |
| // Try to get the host IP. |
| String host = InetAddress.getLocalHost().toString(); |
| // This hash is content - based, not the address based. |
| hostIpHash = host.hashCode(); |
| } |
| catch (Exception e) |
| { |
| // Failed due some reason. |
| hostIpHash = 0; |
| } |
| |
| // Should be the unque address if hashcodes are addresses. |
| // Additionally, add the time when the RMI system was probably started |
| // (this class was first instantiated). |
| return new Object().hashCode() ^ (int) System.currentTimeMillis() |
| ^ hostIpHash; |
| } |
| |
| /** |
| * Get the string representation of this UID. |
| * |
| * @return a string, uniquely identifying this id. |
| */ |
| public String toString() |
| { |
| int max = Character.MAX_RADIX; |
| // Translate into object count, counting from 0. |
| long lc = (count - Short.MIN_VALUE) & 0xFFFF; |
| return Long.toString(unique, max) + ":" + Long.toString(time, max) + "." |
| + Long.toString(lc, max); |
| } |
| } |