Github user dongeforever commented on a diff in the pull request:
https://github.com/apache/incubator-rocketmq/pull/138#discussion_r140401292
--- Diff:
client/src/main/java/org/apache/rocketmq/client/producer/selector/SelectMessageQueueByConsistentHash.java
---
@@ -0,0 +1,132 @@
+/*
+ * 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.rocketmq.client.producer.selector;
+
+import org.apache.rocketmq.client.producer.MessageQueueSelector;
+import org.apache.rocketmq.common.message.Message;
+import org.apache.rocketmq.common.message.MessageQueue;
+
+import java.util.HashMap;
+import java.util.List;
+import java.util.SortedMap;
+import java.util.TreeMap;
+
+/**
+* wanting to send a message with the same key combine with orderly
consumer, user can
+* use the implements of the MessageQueueSelector, which has one
optimization compared with SelectMessageQueueByHash
+* when a broker crash , it can reduce the message Arriving out of the order
+*/
+public class SelectMessageQueueByConsistentHash implements
MessageQueueSelector {
+
+ private volatile SortedMap<Integer, String> virtualNodes =
+ new TreeMap<Integer, String>();
+
+ private static final int DEFAULT_VIRTUAL_NODES = 100;
+
+ private final int virtualNodeNum;
+
+ private volatile HashMap<String, MessageQueue> idToQueueMap = new
HashMap<String, MessageQueue>();
+
+ public SelectMessageQueueByConsistentHash() {
+ this.virtualNodeNum = DEFAULT_VIRTUAL_NODES;
+ }
+
+ public SelectMessageQueueByConsistentHash(int virtualNodeNum) {
+ this.virtualNodeNum = virtualNodeNum;
+ }
+
+ @Override
+ public MessageQueue select(List<MessageQueue> mqs, Message msg, Object
arg) {
+ synchronized (this) {
+ if (queueChange(mqs)) {
+ reloadConsistentHash(mqs);
+ }
+
+ String uniqueQueueId = getMsgQueueIdBy(arg.toString());
+ MessageQueue messageQueue = idToQueueMap.get(uniqueQueueId);
+ return messageQueue;
+ }
+ }
+
+ private boolean queueChange(List<MessageQueue> mqs) {
+ if (mqs.size() != this.idToQueueMap.size()) {
+ return true;
+ }
+
+ for (MessageQueue queue : mqs) {
+ String id = queue.getTopic() + "_" + queue.getBrokerName() +
"_" + queue.getQueueId();
+ if (!this.idToQueueMap.containsKey(id)) {
+ return true;
+ }
+ }
+
+ return false;
+ }
+
+ private String getMsgQueueIdBy(String arg) {
+ int hash = getHash(arg);
+ SortedMap<Integer, String> subMap = virtualNodes.tailMap(hash);
+
+ Integer i;
+ String virtualNode;
+
+ if (subMap.size() == 0) {
+ i = virtualNodes.firstKey();
+ virtualNode = virtualNodes.get(i);
+ } else {
+ i = subMap.firstKey();
+ virtualNode = subMap.get(i);
+ }
+
+ String result = virtualNode.substring(0,
virtualNode.indexOf("&&"));
+ return result;
+ }
+
+ private int getHash(String str) {
--- End diff --
Why not just use str.hashCode?
---
