rocketmq发送消息之寻找主题路由信息

1、rocket发送消息整个过程可以概括为：检查消息->寻找主题路由信息->选择消息队列->发送消息，本文主要解析寻找主题路由信息部分。
2、以rocketMq源码中的示例开始解读，入口是excample模块中的Producer#send()方法

SendResult sendResult = producer.send(msg);

DefaultMQProducerImpl#sendDefaultImpl方法

Validators.checkMessage(msg, this.defaultMQProducer);
        final long invokeID = random.nextLong();
        long beginTimestampFirst = System.currentTimeMillis();
        long beginTimestampPrev = beginTimestampFirst;
        long endTimestamp = beginTimestampFirst;
        TopicPublishInfo topicPublishInfo = 
#寻找主题路由信息入口，如果寻找不到路由信息，直接抛出异常信息
this.tryToFindTopicPublishInfo(msg.getTopic());
        if (topicPublishInfo != null && topicPublishInfo.ok()) {
            boolean callTimeout = false;
            MessageQueue mq = null;

DefaultMQProducerImpl#tryToFindTopicPublishInfo方法,第一次发送消息时，先从缓存中获取路由信息，如果没有获取到，则从NameServer查找主题信息，如果获取则返回，并且将主题信息放入缓存，如果还未获取到则从NameServer查询默认的主题信息

private TopicPublishInfo tryToFindTopicPublishInfo(final String topic) {
        TopicPublishInfo topicPublishInfo = this.topicPublishInfoTable.get(topic);
        if (null == topicPublishInfo || !topicPublishInfo.ok()) {
            this.topicPublishInfoTable.putIfAbsent(topic, new TopicPublishInfo());
            this.mQClientFactory.updateTopicRouteInfoFromNameServer(topic);
            topicPublishInfo = this.topicPublishInfoTable.get(topic);
        }

        if (topicPublishInfo.isHaveTopicRouterInfo() || topicPublishInfo.ok()) {
            return topicPublishInfo;
        } else {
            this.mQClientFactory.updateTopicRouteInfoFromNameServer(topic, true, this.defaultMQProducer);
            topicPublishInfo = this.topicPublishInfoTable.get(topic);
            return topicPublishInfo;
        }
    }

MQClientInstance#updateTopicRouteInfoFromNameServer方法从NameServer查询主题信息

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;
                    #获取默认主题
                    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 {
                        #从NameSever获取指定的主题路由信息，底层使用Netty
                        topicRouteData = this.mQClientAPIImpl.getTopicRouteInfoFromNameServer(topic, 1000 * 3);
                    }
                    if (topicRouteData != null) {
                        #因为之前在DefaultMQProducerImpl中已经缓存了主题路由信息，包括空的主题路由信息，因此这里需要检查是否要更新
                        TopicRouteData old = this.topicRouteTable.get(topic);
                        #比较时是将两个目标对象深度克隆后进行比对，防止影响原来的目标对象
                        boolean changed = topicRouteDataIsChange(old, topicRouteData);
                        if (!changed) {
                            changed = this.isNeedUpdateTopicRouteInfo(topic);
                        } else {
                            log.info("the topic[{}] route info changed, old[{}] ,new[{}]", topic, old, topicRouteData);
                        }
                        #如果需要更新，这更新DefaultMQProducerImpl
                        if (changed) {
                            TopicRouteData cloneTopicRouteData = topicRouteData.cloneTopicRouteData();
                            #更新topic的broker地址信息
                            for (BrokerData bd : topicRouteData.getBrokerDatas()) {
                                this.brokerAddrTable.put(bd.getBrokerName(), bd.getBrokerAddrs());
                            }

                            // Update Pub info 更新DefaultMQProducerImpl中的topicPublishInfoTable缓存信息
                            {
                                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更新消费者信息
                            {
                                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);
                            #将原始的主题路由信息放入缓存
                            this.topicRouteTable.put(topic, cloneTopicRouteData);
                            return true;
                        }
                    } else {
                        log.warn("updateTopicRouteInfoFromNameServer, getTopicRouteInfoFromNameServer return null, Topic: {}", topic);
                    }
                } catch (MQClientException e) {
                    if (!topic.startsWith(MixAll.RETRY_GROUP_TOPIC_PREFIX)) {
                        log.warn("updateTopicRouteInfoFromNameServer Exception", e);
                    }
                } catch (RemotingException e) {
                    log.error("updateTopicRouteInfoFromNameServer Exception", e);
                    throw new IllegalStateException(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;
    }

MQClientInstance#topicRouteData2TopicPublishInfo方法从TopicRouteData路由信息中获取主题发布相关信息

public static TopicPublishInfo topicRouteData2TopicPublishInfo(final String topic, final TopicRouteData route) {
        TopicPublishInfo info = new TopicPublishInfo();
        info.setTopicRouteData(route);
        #设置有序broker信息list
        if (route.getOrderTopicConf() != null && route.getOrderTopicConf().length() > 0) {
            String[] brokers = route.getOrderTopicConf().split(";");
            for (String broker : brokers) {
                String[] item = broker.split(":");
                int nums = Integer.parseInt(item[1]);
                for (int i = 0; i < nums; i++) {
                    MessageQueue mq = new MessageQueue(topic, item[0], i);
                    info.getMessageQueueList().add(mq);
                }
            }

            info.setOrderTopic(true);
        } else {
            List<QueueData> qds = route.getQueueDatas();
            Collections.sort(qds);
            for (QueueData qd : qds) {
                #只获取有写权限的队列
                if (PermName.isWriteable(qd.getPerm())) {
                    BrokerData brokerData = null;
                    for (BrokerData bd : route.getBrokerDatas()) {
                        if (bd.getBrokerName().equals(qd.getBrokerName())) {
                            brokerData = bd;
                            break;
                        }
                    }

                    if (null == brokerData) {
                        continue;
                    }
                    #只使用master节点
                    if (!brokerData.getBrokerAddrs().containsKey(MixAll.MASTER_ID)) {
                        continue;
                    }

                    for (int i = 0; i < qd.getWriteQueueNums(); i++) {
                        MessageQueue mq = new MessageQueue(topic, qd.getBrokerName(), i);
                        info.getMessageQueueList().add(mq);
                    }
                }
            }

            info.setOrderTopic(false);
        }

        return info;
    }

具体请求NameServer的主题路由信息省略，到此，第一次发送消息获取主题路由信息就已完成。