com.alibaba.dubbo.rpc.cluster.loadbalance.ConsistentHashLoadBalance Maven / Gradle / Ivy

Go to download
Show more of this group Show more artifacts with this name
Show all versions of dubbo2 Show documentation
The all in one project of dubbo2
The newest version!
/*
 * Copyright 1999-2012 Alibaba Group.
 *  
 * Licensed 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 com.alibaba.dubbo.rpc.cluster.loadbalance;

import java.io.UnsupportedEncodingException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.List;
import java.util.SortedMap;
import java.util.TreeMap;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;

import com.alibaba.dubbo.common.Constants;
import com.alibaba.dubbo.common.URL;
import com.alibaba.dubbo.rpc.Invocation;
import com.alibaba.dubbo.rpc.Invoker;

/**
 * ConsistentHashLoadBalance
 * 
 * @author william.liangf
 */
public class ConsistentHashLoadBalance extends AbstractLoadBalance {

    private final ConcurrentMap> selectors = new ConcurrentHashMap>();

    @SuppressWarnings("unchecked")
    @Override
    protected  Invoker doSelect(List> invokers, URL url, Invocation invocation) {
        String key = invokers.get(0).getUrl().getServiceKey() + "." + invocation.getMethodName();
        int identityHashCode = System.identityHashCode(invokers);
        ConsistentHashSelector selector = (ConsistentHashSelector) selectors.get(key);
        if (selector == null || selector.getIdentityHashCode() != identityHashCode) {
            selectors.put(key, new ConsistentHashSelector(invokers, invocation.getMethodName(), identityHashCode));
            selector = (ConsistentHashSelector) selectors.get(key);
        }
        return selector.select(invocation);
    }

    private static final class ConsistentHashSelector {

        private final TreeMap> virtualInvokers;

        private final int                       replicaNumber;
        
        private final int                       identityHashCode;
        
        private final int[]                     argumentIndex;

        public ConsistentHashSelector(List> invokers, String methodName, int identityHashCode) {
            this.virtualInvokers = new TreeMap>();
            this.identityHashCode = System.identityHashCode(invokers);
            URL url = invokers.get(0).getUrl();
            this.replicaNumber = url.getMethodParameter(methodName, "hash.nodes", 160);
            String[] index = Constants.COMMA_SPLIT_PATTERN.split(url.getMethodParameter(methodName, "hash.arguments", "0"));
            argumentIndex = new int[index.length];
            for (int i = 0; i < index.length; i ++) {
                argumentIndex[i] = Integer.parseInt(index[i]);
            }
            for (Invoker invoker : invokers) {
                for (int i = 0; i < replicaNumber / 4; i++) {
                    byte[] digest = md5(invoker.getUrl().toFullString() + i);
                    for (int h = 0; h < 4; h++) {
                        long m = hash(digest, h);
                        virtualInvokers.put(m, invoker);
                    }
                }
            }
        }

        public int getIdentityHashCode() {
            return identityHashCode;
        }

        public Invoker select(Invocation invocation) {
            String key = toKey(invocation.getArguments());
            byte[] digest = md5(key);
            Invoker invoker = sekectForKey(hash(digest, 0));
            return invoker;
        }

        private String toKey(Object[] args) {
            StringBuilder buf = new StringBuilder();
            for (int i : argumentIndex) {
                if (i >= 0 && i < args.length) {
                    buf.append(args[i]);
                }
            }
            return buf.toString();
        }

        private Invoker sekectForKey(long hash) {
            Invoker invoker;
            Long key = hash;
            if (!virtualInvokers.containsKey(key)) {
                SortedMap> tailMap = virtualInvokers.tailMap(key);
                if (tailMap.isEmpty()) {
                    key = virtualInvokers.firstKey();
                } else {
                    key = tailMap.firstKey();
                }
            }
            invoker = virtualInvokers.get(key);
            return invoker;
        }

        private long hash(byte[] digest, int number) {
            return (((long) (digest[3 + number * 4] & 0xFF) << 24)
                    | ((long) (digest[2 + number * 4] & 0xFF) << 16)
                    | ((long) (digest[1 + number * 4] & 0xFF) << 8) 
                    | (digest[0 + number * 4] & 0xFF)) 
                    & 0xFFFFFFFFL;
        }

        private byte[] md5(String value) {
            MessageDigest md5;
            try {
                md5 = MessageDigest.getInstance("MD5");
            } catch (NoSuchAlgorithmException e) {
                throw new IllegalStateException(e.getMessage(), e);
            }
            md5.reset();
            byte[] bytes = null;
            try {
                bytes = value.getBytes("UTF-8");
            } catch (UnsupportedEncodingException e) {
                throw new IllegalStateException(e.getMessage(), e);
            }
            md5.update(bytes);
            return md5.digest();
        }

    }

}