从RocketMQ架构解析中我们了解到了RocketMQ的架构设计原理，接下来我们根据架构图来解析各个步骤的源码，探索RocketMQ是怎么实现相关功能的，从Producer发送消息开始。
下面是Producer发送一条消息的流程图
1.从本地获取该条消息应该发送给哪个broker，对应的topic等等信息
2.如果获取不到，就通过与NameSrv交互进行获取
3.获取到相关信息后，进行消息发送，返回结果
本文重点来看获取topicInfo的方法tryToFindTopicPublishInfo
private TopicPublishInfo tryToFindTopicPublishInfo(final String topic) {
//步骤1.1
TopicPublishInfo topicPublishInfo = this.topicPublishInfoTable.get(topic);
if (null == topicPublishInfo || !topicPublishInfo.ok()) {
//步骤1.2
this.topicPublishInfoTable.putIfAbsent(topic, new TopicPublishInfo());
//步骤1.3
this.mQClientFactory.updateTopicRouteInfoFromNameServer(topic);
topicPublishInfo = this.topicPublishInfoTable.get(topic);
}
if (topicPublishInfo.isHaveTopicRouterInfo() || topicPublishInfo.ok()) {
return topicPublishInfo;
} else {
//步骤1.4
this.mQClientFactory.updateTopicRouteInfoFromNameServer(topic, true, this.defaultMQProducer);
topicPublishInfo = this.topicPublishInfoTable.get(topic);
return topicPublishInfo;
}
}
1.首先从topicPublishInfoTable（本地存储的路由信息表）中获取
2.如果获取不到，先在topicPublishInfoTable插入一个new出来的TopicPublishInfo，key为topic
3.然后通过updateTopicRouteInfoFromNameServer方法从NameServer中获取相关信息
4.如果NameServer中也拿不到，使用 {DefaultMQProducer#createTopicKey} 对应的 Topic发布信息。目的是当 Broker 开启自动创建 Topic开关时，Broker 接收到消息后自动创建Topic
步骤1.1、1.2就是操作topicPublishInfoTable的get和putIfAbsent方法，不再细分，我们来看步骤1.3
public boolean updateTopicRouteInfoFromNameServer(final String topic) {
return updateTopicRouteInfoFromNameServer(topic, false, null);
}
public boolean updateTopicRouteInfoFromNameServer(final String topic, boolean isDefault,
DefaultMQProducer defaultMQProducer) {
try {
if (this.lockNamesrv.tryLock(LOCK_TIMEOUT_MILLIS, TimeUnit.MILLISECONDS)) {
try {
TopicRouteData topicRouteData;
//步骤1.3.1：判断条件
if (isDefault && defaultMQProducer != null) {
topicRouteData = this.mQClientAPIImpl.getDefaultTopicRouteInfoFromNameServer(defaultMQProducer.getCreateTopicKey(),
1000 * 3);
if (topicRouteData != null) {
for (QueueData data : topicRouteData.getQueueDatas()) {
int queueNums = Math.min(defaultMQProducer.getDefaultTopicQueueNums(), data.getReadQueueNums());
data.setReadQueueNums(queueNums);
data.setWriteQueueNums(queueNums);
}
}
} else {
//步骤1.3.2：通过MQClient来获取该topic对应的在Namesrv的信息
topicRouteData = this.mQClientAPIImpl.getTopicRouteInfoFromNameServer(topic, 1000 * 3);
}
if (topicRouteData != null) {
TopicRouteData old = this.topicRouteTable.get(topic);
boolean changed = topicRouteDataIsChange(old, topicRouteData);
if (!changed) {
changed = this.isNeedUpdateTopicRouteInfo(topic);
} else {
log.info("the topic[{}] route info changed, old[{}] ,new[{}]", topic, old, topicRouteData);
}
//步骤1.3.3：更新TopicRouteData 和相关信息
if (changed) {
TopicRouteData cloneTopicRouteData = topicRouteData.cloneTopicRouteData();
for (BrokerData bd : topicRouteData.getBrokerDatas()) {
this.brokerAddrTable.put(bd.getBrokerName(), bd.getBrokerAddrs());
}
// Update Pub info
{
TopicPublishInfo publishInfo = topicRouteData2TopicPublishInfo(topic, topicRouteData);
publishInfo.setHaveTopicRouterInfo(true);
Iterator<Entry<String, MQProducerInner>> it = this.producerTable.entrySet().iterator();
while (it.hasNext()) {
Entry<String, MQProducerInner> entry = it.next();
MQProducerInner impl = entry.getValue();
if (impl != null) {
impl.updateTopicPublishInfo(topic, publishInfo);
}
}
}
// Update sub info
{
Set<MessageQueue> subscribeInfo = topicRouteData2TopicSubscribeInfo(topic, topicRouteData);
Iterator<Entry<String, MQConsumerInner>> it = this.consumerTable.entrySet().iterator();
while (it.hasNext()) {
Entry<String, MQConsumerInner> entry = it.next();
MQConsumerInner impl = entry.getValue();
if (impl != null) {
impl.updateTopicSubscribeInfo(topic, subscribeInfo);
}
}
}
log.info("topicRouteTable.put. Topic = {}, TopicRouteData[{}]", topic, cloneTopicRouteData);
this.topicRouteTable.put(topic, cloneTopicRouteData);
return true;
}
} else {
log.warn("updateTopicRouteInfoFromNameServer, getTopicRouteInfoFromNameServer return null, Topic: {}", topic);
}
} catch (Exception e) {
if (!topic.startsWith(MixAll.RETRY_GROUP_TOPIC_PREFIX) && !topic.equals(MixAll.DEFAULT_TOPIC)) {
log.warn("updateTopicRouteInfoFromNameServer Exception", e);
}
} finally {
this.lockNamesrv.unlock();
}
} else {
log.warn("updateTopicRouteInfoFromNameServer tryLock timeout {}ms", LOCK_TIMEOUT_MILLIS);
}
} catch (InterruptedException e) {
log.warn("updateTopicRouteInfoFromNameServer Exception", e);
}
return false;
}
这个方法的三个主要步骤已经在源码里注释了，最后通过MQClient来访问Namesrv来获取topicRouteData，由于这是第一次进行发送信息，所以Namesrv是空的，获取不到。
执行完1.3的源码，由于此时topicPublishInfo 还是不满足条件所以会进入1.4步骤
this.mQClientFactory.updateTopicRouteInfoFromNameServer(topic, true, this.defaultMQProducer);
这个方法调用的就是1.3的方法，只是入参不同而已，此时会进入步骤1.3.1和1.3.2之间的代码
topicRouteData = this.mQClientAPIImpl.getDefaultTopicRouteInfoFromNameServer(defaultMQProducer.getCreateTopicKey(),
1000 * 3);
if (topicRouteData != null) {
for (QueueData data : topicRouteData.getQueueDatas()) {
int queueNums = Math.min(defaultMQProducer.getDefaultTopicQueueNums(), data.getReadQueueNums());
data.setReadQueueNums(queueNums);
data.setWriteQueueNums(queueNums);
}
}
这时将会请求Namesrv并返回{DefaultMQProducer#createTopicKey} 对应的topicRouteData ，然后再根据入参传进来的defaultMQProducer的配置初始化topicRouteData的QueueDatas配置，之后执行步骤1.3.3后面的代码
//Update Pub info
{
TopicPublishInfo publishInfo = topicRouteData2TopicPublishInfo(topic, topicRouteData);
publishInfo.setHaveTopicRouterInfo(true);
Iterator<Entry<String, MQProducerInner>> it = this.producerTable.entrySet().iterator();
while (it.hasNext()) {
Entry<String, MQProducerInner> entry = it.next();
MQProducerInner impl = entry.getValue();
if (impl != null) {
impl.updateTopicPublishInfo(topic, publishInfo);
}
}
}
注意：我们最终是想得到TopicPublishInfo的，在这里循环this.producerTable，然后把TopicPublishInfo赋值给了producerTable里的每一个impl，此时我们需要搞清楚这几个东西之间的关系和含义了
一个生产者拥有一个topicPublishInfoTable
private final ConcurrentMap<String/* topic */, TopicPublishInfo> topicPublishInfoTable =
new ConcurrentHashMap<String, TopicPublishInfo>();
topicPublishInfoTable里是key为topic，value为TopicPublishInfo的元素
一个生产者组拥有一个producerTable
private final ConcurrentMap<String/* group */, MQProducerInner> producerTable = new ConcurrentHashMap<String, MQProducerInner>();
key为生产者组名称，value为MQProducerInner，对应着一个生产者
我们再来看上述循环的核心代码
impl.updateTopicPublishInfo(topic, publishInfo);
public void updateTopicPublishInfo(final String topic, final TopicPublishInfo info) {
if (info != null && topic != null) {
TopicPublishInfo prev = this.topicPublishInfoTable.put(topic, info);
if (prev != null) {
log.info("updateTopicPublishInfo prev is not null, " + prev.toString());
}
}
}
在这里，为生产者的topicPublishInfoTableput进去了我们所需要的TopicPublishInfo，这时我们在执行步骤1.4后续代码时就可以拿到我们要的TopicPublishInfo了。
获取TopicPublishInfo总结
1.先拿本地内存中该topic的TopicPublishInfo
2.本地内存没有，查询Namesrv
3.如果Namesrv中也没用，就使用默认的DefaultMQProducer对应的TopicPublishInfo
4.发送成功后，当 Broker 开启自动创建 Topic开关时，Broker 接收到消息后自动创建Topic，这时候，该生产者的TopicPublishInfo就会存在于broker和Namesrv中了。
上述就是sendMessage获取TopicPublishInfo对象的分析了。
