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/*
* 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.dubbo.rpc.cluster.loadbalance;
import org.apache.dubbo.common.URL;
import org.apache.dubbo.common.io.Bytes;
import org.apache.dubbo.rpc.Invocation;
import org.apache.dubbo.rpc.Invoker;
import org.apache.dubbo.rpc.support.RpcUtils;
import java.util.List;
import java.util.Map;
import java.util.TreeMap;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.atomic.AtomicLong;
import static org.apache.dubbo.common.constants.CommonConstants.COMMA_SPLIT_PATTERN;
/**
* ConsistentHashLoadBalance
*/
public class ConsistentHashLoadBalance extends AbstractLoadBalance {
public static final String NAME = "consistenthash";
/**
* Hash nodes name
*/
public static final String HASH_NODES = "hash.nodes";
/**
* Hash arguments name
*/
public static final String HASH_ARGUMENTS = "hash.arguments";
private final ConcurrentMap> selectors = new ConcurrentHashMap>();
@SuppressWarnings("unchecked")
@Override
protected Invoker doSelect(List> invokers, URL url, Invocation invocation) {
String methodName = RpcUtils.getMethodName(invocation);
String key = invokers.get(0).getUrl().getServiceKey() + "." + methodName;
// using the hashcode of list to compute the hash only pay attention to the elements in the list
int invokersHashCode = getCorrespondingHashCode(invokers);
ConsistentHashSelector selector = (ConsistentHashSelector) selectors.get(key);
if (selector == null || selector.identityHashCode != invokersHashCode) {
selectors.put(key, new ConsistentHashSelector(invokers, methodName, invokersHashCode));
selector = (ConsistentHashSelector) selectors.get(key);
}
return selector.select(invocation);
}
/**
* get hash code of invokers
* Make this method to public in order to use this method in test case
* @param invokers
* @return
*/
public int getCorrespondingHashCode(List> invokers){
return invokers.hashCode();
}
private static final class ConsistentHashSelector {
private final TreeMap> virtualInvokers;
private final int replicaNumber;
private final int identityHashCode;
private final int[] argumentIndex;
/**
* key: server(invoker) address
* value: count of requests accept by certain server
*/
private Map serverRequestCountMap = new ConcurrentHashMap<>();
/**
* count of total requests accept by all servers
*/
private AtomicLong totalRequestCount;
/**
* count of current servers(invokers)
*/
private int serverCount;
/**
* the ratio which allow count of requests accept by each server
* overrate average (totalRequestCount/serverCount).
* 1.5 is recommended, in the future we can make this param configurable
*/
private static final double OVERLOAD_RATIO_THREAD = 1.5F;
ConsistentHashSelector(List> invokers, String methodName, int identityHashCode) {
this.virtualInvokers = new TreeMap>();
this.identityHashCode = identityHashCode;
URL url = invokers.get(0).getUrl();
this.replicaNumber = url.getMethodParameter(methodName, HASH_NODES, 160);
String[] index = 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) {
String address = invoker.getUrl().getAddress();
for (int i = 0; i < replicaNumber / 4; i++) {
byte[] digest = Bytes.getMD5(address + i);
for (int h = 0; h < 4; h++) {
long m = hash(digest, h);
virtualInvokers.put(m, invoker);
}
}
}
totalRequestCount = new AtomicLong(0);
serverCount = invokers.size();
serverRequestCountMap.clear();
}
public Invoker select(Invocation invocation) {
String key = toKey(invocation.getArguments());
byte[] digest = Bytes.getMD5(key);
return selectForKey(hash(digest, 0));
}
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 selectForKey(long hash) {
Map.Entry> entry = virtualInvokers.ceilingEntry(hash);
if (entry == null) {
entry = virtualInvokers.firstEntry();
}
String serverAddress = entry.getValue().getUrl().getAddress();
/**
* The following part of codes aims to select suitable invoker.
* This part is not complete thread safety.
* However, in the scene of consumer-side load balance,
* thread race for this part of codes
* (execution time cost for this part of codes without any IO or
* network operation is very low) will rarely occur. And even in
* extreme case, a few requests are assigned to an invoker which
* is above OVERLOAD_RATIO_THREAD will not make a significant impact
* on the effect of this new algorithm.
* And make this part of codes synchronized will reduce efficiency of
* every request. In my opinion, this is not worth. So it is not a
* problem for this part is not complete thread safety.
*/
double overloadThread = ((double) totalRequestCount.get() / (double) serverCount) * OVERLOAD_RATIO_THREAD;
/**
* Find a valid server node:
* 1. Not have accept request yet
* or
* 2. Not have overloaded (request count already accept < thread (average request count * overloadRatioAllowed ))
*/
while (serverRequestCountMap.containsKey(serverAddress)
&& serverRequestCountMap.get(serverAddress).get() >= overloadThread) {
/**
* If server node is not valid, get next node
*/
entry = getNextInvokerNode(virtualInvokers, entry);
serverAddress = entry.getValue().getUrl().getAddress();
}
if (!serverRequestCountMap.containsKey(serverAddress)) {
serverRequestCountMap.put(serverAddress, new AtomicLong(1));
} else {
serverRequestCountMap.get(serverAddress).incrementAndGet();
}
totalRequestCount.incrementAndGet();
return entry.getValue();
}
private Map.Entry> getNextInvokerNode(TreeMap> virtualInvokers, Map.Entry> entry){
Map.Entry> nextEntry = virtualInvokers.higherEntry(entry.getKey());
if(nextEntry == null){
return virtualInvokers.firstEntry();
}
return nextEntry;
}
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[number * 4] & 0xFF))
& 0xFFFFFFFFL;
}
}
}
