bundles/org.apache.tomcat/src/org/apache/catalina/tribes/group/AbsoluteOrder.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.catalina.tribes.group;

import java.io.Serializable;
import java.util.Arrays;
import java.util.Comparator;
import java.util.List;

import org.apache.catalina.tribes.Member;

/**
 * <p>Title: Membership - Absolute Order</p>
 *
 * <p>Description: A simple, yet agreeable and efficient way of ordering members</p>
 * <p>
 *    Ordering members can serve as a basis for electing a leader or coordinating efforts.<br>
 *    This is stinky simple, it works on the basis of the <code>Member</code> interface
 *    and orders members in the following format:
 * 
 *  <ol>
 *     <li>IP comparison - byte by byte, lower byte higher rank</li>
 *     <li>IPv4 addresses rank higher than IPv6, ie the lesser number of bytes, the higher rank</li>
 *     <li>Port comparison - lower port, higher rank</li>
 *     <li>UniqueId comparison- byte by byte, lower byte higher rank</li>
 *  </ol>
 *     
 * </p>
 *
 * @author Filip Hanik
 * @version 1.0
 * @see org.apache.catalina.tribes.Member
 */
public class AbsoluteOrder {
    public static final AbsoluteComparator comp = new AbsoluteComparator();
    
    protected AbsoluteOrder() {
        super();
    }


    public static void absoluteOrder(Member[] members) {
        if ( members == null || members.length <= 1 ) return;
        Arrays.sort(members,comp);
    }
    
    public static void absoluteOrder(List<Member> members) {
        if ( members == null || members.size() <= 1 ) return;
        java.util.Collections.sort(members, comp);
    }
    
    public static class AbsoluteComparator implements Comparator<Member>,
            Serializable {
        
        private static final long serialVersionUID = 1L;

        @Override
        public int compare(Member m1, Member m2) {
            int result = compareIps(m1,m2);
            if ( result == 0 ) result = comparePorts(m1,m2);
            if ( result == 0 ) result = compareIds(m1,m2);
            return result;
        }
        
        public int compareIps(Member m1, Member m2) {
            return compareBytes(m1.getHost(),m2.getHost());
        }
        
        public int comparePorts(Member m1, Member m2) {
            return compareInts(m1.getPort(),m2.getPort());
        }
        
        public int compareIds(Member m1, Member m2) {
            return compareBytes(m1.getUniqueId(),m2.getUniqueId());
        }
        
        protected int compareBytes(byte[] d1, byte[] d2) {
            int result = 0;
            if ( d1.length == d2.length ) {
                for (int i=0; (result==0) && (i<d1.length); i++) {
                    result = compareBytes(d1[i],d2[i]);
                }
            } else if ( d1.length < d2.length) {
                result = -1;
            } else {
                result = 1;
            }
            return result;
        }
        
        protected int compareBytes(byte b1, byte b2) {
            return compareInts(b1,b2);
        }
        
        protected int compareInts(int b1, int b2) {
            int result = 0;
            if ( b1 == b2 ) {

            } else if ( b1 < b2) {
                result = -1;
            } else {
                result = 1;
            }
            return result;
        }
    }
    
}