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基于rocketmq-4.9.0 版本分析rocketmq
消费者代码举例:
public class Consumer {
public static void main(String[] args) throws InterruptedException, MQClientException {
// 实例化消费者
DefaultMQPushConsumer consumer = new DefaultMQPushConsumer("c1-group");
// 设置NameServer的地址
consumer.setNamesrvAddr("127.0.0.1:9876");
//TODO:订阅一个或者多个Topic,以及Tag来过滤需要消费的消息
consumer.subscribe("test_topic", "*");
// TODO: 注册消息监听器,用来消费消息
consumer.registerMessageListener(new MessageListenerConcurrently() {
@Override
public ConsumeConcurrentlyStatus consumeMessage(List<MessageExt> msgs,
ConsumeConcurrentlyContext context) {
try {
System.out.printf("%s Receive New Messages: %s %n", Thread.currentThread().getName(), msgs);
boolean consume = new Random().nextBoolean();
if(!consume) {
//TODO:消费失败,等待重试
return ConsumeConcurrentlyStatus.RECONSUME_LATER;
}
} catch (Exception e) {
e.printStackTrace();
return ConsumeConcurrentlyStatus.RECONSUME_LATER;
}
//TODO: 消费成功
return ConsumeConcurrentlyStatus.CONSUME_SUCCESS;
}
});
//TODO: 启动消费者实例
consumer.start();
System.out.printf("Consumer Started.%n");
}
}
2.客户端start()方法都干了什么?
首先,暴露给开发者的 DefaultMQPushConsumer
是一个外观类,真正工作的是其内部的DefaultMQPushConsumerImpl
,所以我们看下DefaultMQPushConsumerImpl#start()
的逻辑
内容非常的多,我会在代码上添加一些注释
public synchronized void start() throws MQClientException {
switch (this.serviceState) {
case CREATE_JUST:
log.info("the consumer [{}] start beginning. messageModel={}, isUnitMode={}", this.defaultMQPushConsumer.getConsumerGroup(),
this.defaultMQPushConsumer.getMessageModel(), this.defaultMQPushConsumer.isUnitMode());
this.serviceState = ServiceState.START_FAILED;
//TODO:检查配置,比如消费者组是否为空,消费模式是否为空,订阅信息是否为空等等
this.checkConfig();
//TODO: 拷贝订阅关系,大概就是将订阅关系设置到重平衡服务类中
this.copySubscription();
if (this.defaultMQPushConsumer.getMessageModel() == MessageModel.CLUSTERING) {
this.defaultMQPushConsumer.changeInstanceNameToPID();
}
//TODO:创建客户端实例对象
this.mQClientFactory = MQClientManager.getInstance().getOrCreateMQClientInstance(this.defaultMQPushConsumer, this.rpcHook);
this.rebalanceImpl.setConsumerGroup(this.defaultMQPushConsumer.getConsumerGroup());
this.rebalanceImpl.setMessageModel(this.defaultMQPushConsumer.getMessageModel());
this.rebalanceImpl.setAllocateMessageQueueStrategy(this.defaultMQPushConsumer.getAllocateMessageQueueStrategy());
this.rebalanceImpl.setmQClientFactory(this.mQClientFactory);
//TODO: 创建拉取对象的核心类,后面去broker拉取消息时会看到
this.pullAPIWrapper = new PullAPIWrapper(
mQClientFactory,
this.defaultMQPushConsumer.getConsumerGroup(), isUnitMode());
this.pullAPIWrapper.registerFilterMessageHook(filterMessageHookList);
if (this.defaultMQPushConsumer.getOffsetStore() != null) {
this.offsetStore = this.defaultMQPushConsumer.getOffsetStore();
} else {
switch (this.defaultMQPushConsumer.getMessageModel()) {
case BROADCASTING:
//TODO: 广播模式创建LocalFileOffsetStore,保存offset到本地文件中
this.offsetStore = new LocalFileOffsetStore(this.mQClientFactory, this.defaultMQPushConsumer.getConsumerGroup());
break;
case CLUSTERING:
//TODO:集群模式创建 RemoteBrokerOffsetStore,保存offset到broker文件中
this.offsetStore = new RemoteBrokerOffsetStore(this.mQClientFactory, this.defaultMQPushConsumer.getConsumerGroup());
break;
default:
break;
}
this.defaultMQPushConsumer.setOffsetStore(this.offsetStore);
}
this.offsetStore.load();
if (this.getMessageListenerInner() instanceof MessageListenerOrderly) {
this.consumeOrderly = true;
//TODO:创建顺序消费消息服务类
this.consumeMessageService =
new ConsumeMessageOrderlyService(this, (MessageListenerOrderly) this.getMessageListenerInner());
} else if (this.getMessageListenerInner() instanceof MessageListenerConcurrently) {
this.consumeOrderly = false;
//TODO:创建其他消费消息服务类,其内部维护了一个线程池,后面会用到
this.consumeMessageService =
new ConsumeMessageConcurrentlyService(this, (MessageListenerConcurrently) this.getMessageListenerInner());
}
this.consumeMessageService.start();
//TODO:注册consumer到本地
boolean registerOK = mQClientFactory.registerConsumer(this.defaultMQPushConsumer.getConsumerGroup(), this);
if (!registerOK) {
this.serviceState = ServiceState.CREATE_JUST;
this.consumeMessageService.shutdown(defaultMQPushConsumer.getAwaitTerminationMillisWhenShutdown());
throw new MQClientException("The consumer group[" + this.defaultMQPushConsumer.getConsumerGroup()
+ "] has been created before, specify another name please." + FAQUrl.suggestTodo(FAQUrl.GROUP_NAME_DUPLICATE_URL),
null);
}
//启动客户端实例,这个方法非常重要,内部做了很多事情,后面会说
mQClientFactory.start();
log.info("the consumer [{}] start OK.", this.defaultMQPushConsumer.getConsumerGroup());
this.serviceState = ServiceState.RUNNING;
break;
case RUNNING:
case START_FAILED:
case SHUTDOWN_ALREADY:
throw new MQClientException("The PushConsumer service state not OK, maybe started once, "
+ this.serviceState
+ FAQUrl.suggestTodo(FAQUrl.CLIENT_SERVICE_NOT_OK),
null);
default:
break;
}
this.updateTopicSubscribeInfoWhenSubscriptionChanged();
this.mQClientFactory.checkClientInBroker();
//TODO:发送消息到broker
this.mQClientFactory.sendHeartbeatToAllBrokerWithLock();
//TODO:立即重平衡
this.mQClientFactory.rebalanceImmediately();
}
2.1 检查配置
- 校验GroupName是否为空;校验GroupName是否等于DEFAULT_CONSUMER(等于的话直接抛出异常)
- 校验消费模式:集群/广播
- 校验ConsumeFromWhere
- 校验开始消费的指定时间
- 校验AllocateMessageQueueStrategy
- 校验订阅关系
- 校验是否注册消息监听
- 校验消费线程数,
consumeThreadMin
和consumeThreadMax
默认值都是20,取值区间都是 [1, 1000] - 校验本地队列缓存消息的最大数,默认是1000,取值范围是[1, 1024], 主要是做流控用的
- 校验拉取消息的时间间隔,
pullInterval
参数,默认是不存在间隔,取值范围是[0, 65535]。当消费速度比生产速度快,可以设置这个参数,避免花费大概率从broker拉取空消息 - 校验单次拉取的最大消息数,
consumeMessageBatchMaxSize
参数,默认是1,取值范围是[1, 1024] - 校验单次消费的最大消息数,
pullBatchSize
参数,默认是32,取值范围是[1, 1024]。
2.2 拷贝订阅关系
将订阅关系设置到重平衡服务类RebalanceImpl
中
//TODO:key=topic, value=订阅数据(就是tag信息)
protected final ConcurrentMap<String /* topic */, SubscriptionData> subscriptionInner =
new ConcurrentHashMap<String, SubscriptionData>();
2.3 创建客户端实例 MQClientInstance
//TODO: 当后面启动的时候会做很多事情,请继续往后看
this.mQClientFactory = MQClientManager.getInstance().getOrCreateMQClientInstance(this.defaultMQPushConsumer, this.rpcHook);
这个对象在前面分析Producer启动时也看到了,因为Prodcuer/Consumer 都是客户端,所以都会根据这个实例来创建对象。 我们看下这个类的结构:
public class MQClientInstance {
//TODO:生产者表,producer启动时创建一个新的MQClientInstance实例对象,将生产者信息注册到这里。生产者实例对象中消费者信息是空
private final ConcurrentMap<String/* group */, MQProducerInner> producerTable = new ConcurrentHashMap<String, MQProducerInner>();
//TODO:消费者表,consumer启动时创建一个新的MQClientInstance实例对象,将消费者信息注册到这里。消费者实例对象中生产者信息是空
private final ConcurrentMap<String/* group */, MQConsumerInner> consumerTable = new ConcurrentHashMap<String, MQConsumerInner>();
//TODO:topic路由信息,producer和consumer都会使用
private final ConcurrentMap<String/* Topic */, TopicRouteData> topicRouteTable = new ConcurrentHashMap<String, TopicRouteData>();
//TODO:broker信息,producer和consumer都会用到
private final ConcurrentMap<String/* Broker Name */, HashMap<Long/* brokerId */, String/* address */>> brokerAddrTable =
new ConcurrentHashMap<String, HashMap<Long, String>>();
//TODO......
/**
* TODO:构造器
*/
public MQClientInstance(ClientConfig clientConfig, int instanceIndex, String clientId, RPCHook rpcHook) {
//TODO:客户端处理器,比如在集群消费模式下,有新的消费者加入,则通知消费者客户端重平衡,是给消费者用的(分析生产者时,我们直接忽略了它)
this.clientRemotingProcessor = new ClientRemotingProcessor(this);
//TODO:它的内部会创建netty客户端对象(NettyRemotingClient),用于和broker通信
this.mQClientAPIImpl = new MQClientAPIImpl(this.nettyClientConfig, this.clientRemotingProcessor, rpcHook, clientConfig);
//TODO.......
//TODO:拉取消息的服务,和消费者相关
this.pullMessageService = new PullMessageService(this);
//TODO:重平衡服务,和消费者相关
this.rebalanceService = new RebalanceService(this);
//TODO:other......
}
}
所谓的"客户端",实际上是在MQClientAPIImpl
对象的内部的NettyRemotingClient
:
public class MQClientAPIImpl {
//TODO:.....
private final RemotingClient remotingClient;
private final TopAddressing topAddressing;
private final ClientRemotingProcessor clientRemotingProcessor;
private String nameSrvAddr = null;
private ClientConfig clientConfig;
public MQClientAPIImpl(final NettyClientConfig nettyClientConfig,
final ClientRemotingProcessor clientRemotingProcessor,
RPCHook rpcHook, final ClientConfig clientConfig) {
this.clientConfig = clientConfig;
topAddressing = new TopAddressing(MixAll.getWSAddr(), clientConfig.getUnitName());
//TODO:所谓的客户端实际上就是这个,netty客户端
this.remotingClient = new NettyRemotingClient(nettyClientConfig, null);
this.clientRemotingProcessor = clientRemotingProcessor;
this.remotingClient.registerRPCHook(rpcHook);
//TODO:注册处理器
this.remotingClient.registerProcessor(RequestCode.CHECK_TRANSACTION_STATE, this.clientRemotingProcessor, null);
this.remotingClient.registerProcessor(RequestCode.NOTIFY_CONSUMER_IDS_CHANGED, this.clientRemotingProcessor, null);
//TODO:....注册其他处理器......
}
这里我们关注下 NettyRemotingClient
,其实前面分析Broker,Producer时,我们经常看到这个,因为RocketMQ是使用netty作为通信的。
NettyRemotingClient
:netty的客户端对象
NettyRemotingServer
:netty的服务端对象
2.4 创建拉取消息的核心类 PullAPIWrapper
this.pullAPIWrapper = new PullAPIWrapper(
mQClientFactory,
this.defaultMQPushConsumer.getConsumerGroup(), isUnitMode());
2.5 创建 offset存储服务 OffsetStore
- 如果是广播模式(
BROADCASTING
), 则创建LocalFileOffsetStore
对象,将消费者的offset存储到本地的,默认文件路径为当前用户主目录下的 .rocketmq_offsets/{group}/Offsets.json。其中{group}为消费者组名称 - 如果是集群模式(
CLUSTERING
), 则创建RemoteBrokerOffsetStore
对象,将消费者的offset存储到broker中,文件路径为当前用户主目录下的store/config/consumerOffset.json
2.6 创建消费消息的服务类 ConsumeMessageService
- 如果是顺序消费,则创建
ConsumeMessageOrderlyService
对象 - 如果是其他消费,则创建
ConsumeMessageConcurrentlyService
对象,同时内部也会创建一个ThreadPoolExecutor
线程池,这个线程池非常的重要,拉取到消息后会将消息提交到这个线程池中给消费者消费
2.7 将consumer注册到本地
boolean registerOK = mQClientFactory.registerConsumer(this.defaultMQPushConsumer.getConsumerGroup(), this);
将消费者组信息添加到本地客户端实例MQClientInstance
的 consumerTable
Map中,key=groupName; value=DefaultMQPushConsumerImpl
,就是消费者对象
2.8 启动客户端实例(重要)
mQClientFactory.start();
其内部做了很多事情,主要如下:
2.8.1 启动远程netty客户端
// Start request-response channel
this.mQClientAPIImpl.start();
就是启动其内部的 NettyRemotingClient
,用于和broker通信。
2.8.2 启动各种定时任务
// Start various schedule tasks
this.startScheduledTask();
那么有哪些定时任务呢?继续往里看,罗列几个特别关注的
2.8.2.1 发送心跳到Broker
this.scheduledExecutorService.scheduleAtFixedRate(new Runnable() {
@Override
public void run() {
try {
MQClientInstance.this.cleanOfflineBroker();
MQClientInstance.this.sendHeartbeatToAllBrokerWithLock();
} catch (Exception e) {
log.error("ScheduledTask sendHeartbeatToAllBroker exception", e);
}
}
}, 1000, this.clientConfig.getHeartbeatBrokerInterval(), TimeUnit.MILLISECONDS);
延迟1s执行,每隔30s发送一次心跳包
2.8.2.2 持久化消费者的 offset
this.scheduledExecutorService.scheduleAtFixedRate(new Runnable() {
@Override
public void run() {
try {
MQClientInstance.this.persistAllConsumerOffset();
} catch (Exception e) {
log.error("ScheduledTask persistAllConsumerOffset exception", e);
}
}
}, 1000 * 10, this.clientConfig.getPersistConsumerOffsetInterval(), TimeUnit.MILLISECONDS);
延迟10s执行,每隔5s持久化一次offset
这里的持久化是将本地Map中offset发送到broker中,然后broker中的定时任务写到文件中,完成真正的持久化,后面会看到。
2.8.3 启动拉取消息的服务PullMessageService
(重要)
// Start pull service
this.pullMessageService.start();
他是一个异步线程,其核心逻辑是
@Override
public void run() {
log.info(this.getServiceName() + " service started");
while (!this.isStopped()) {
try {
PullRequest pullRequest = this.pullRequestQueue.take();
this.pullMessage(pullRequest);
} catch (InterruptedException ignored) {
} catch (Exception e) {
log.error("Pull Message Service Run Method exception", e);
}
}
log.info(this.getServiceName() + " service end");
}
他会监听阻塞队列pullRequestQueue
,当队列是空的时候,他会一直阻塞,如果不为空,则获取PullRequest
对象,去拉取消息,这个逻辑后面再说。
刚开始肯定是阻塞的,我们要看什么时候往队列中放入值,以及放入值之后做什么
2.8.4 启动重平衡服务 RebalanceService
// Start rebalance service
this.rebalanceService.start();
它也是一个异步线程,其核心逻辑是
@Override
public void run() {
log.info(this.getServiceName() + " service started");
while (!this.isStopped()) {
//TODO:内部使用了juc的CountDownLatch, 使得这里启动后仍然是阻塞的
this.waitForRunning(waitInterval);
this.mqClientFactory.doRebalance();
}
log.info(this.getServiceName() + " service end");
}
他是重平衡的核心逻辑,但是在启动时,由于使用了JUC的 CountDownLatch
锁,使其不会立即重平衡,而是阻塞,什么时候出发重平衡呢?我们还是继续往后看
2.9 发送心跳到broker
this.updateTopicSubscribeInfoWhenSubscriptionChanged();
this.mQClientFactory.checkClientInBroker();
//TODO: 发送心跳到broker
this.mQClientFactory.sendHeartbeatToAllBrokerWithLock();
this.mQClientFactory.rebalanceImmediately();
是不是有些疑惑?前面的定时任务中不是已经启动了心跳服务吗,为什么这里还要启动呢?我也不清楚,猜测是因为担心网络问题导致没有及时发送给broker吧
2.10 立即启动重平衡服务RebalanceService
this.updateTopicSubscribeInfoWhenSubscriptionChanged();
this.mQClientFactory.checkClientInBroker();
//TODO: 发送心跳到broker
this.mQClientFactory.sendHeartbeatToAllBrokerWithLock();
//TODO:立即启动重平衡服务
this.mQClientFactory.rebalanceImmediately();
前面在 2.8.4的时候,启动了重平衡服务,但是因为 CountDownLatch 导致阻塞了,这里就是唤醒,可以执行重平衡的逻辑。
这里先不关注它的内部逻辑,后面在分析。
其实,到这里Consumer客户端启动流程就结束了,至于如何拉取消息,也是这些服务类的相互配合工作的,后面我们在分析Consumer消费流程中在仔细分析它是如何一步一步拉取消息并消费的。
3. 总结
消费者启动过程相比生产者启动过程要复杂一些,会启动很多对象(实际上生产者也启动了,因为他们都是基于客户端实例MQClientInstance
去创建的对象,只不过生产者并不会使用某些服务类)
简单总结下:
- 创建客户端实例
MQClientInstance
(其内部要创建netty客户端对象NettyRemotingClient
) - 启动客户端实例,其内部要启动netty客户端,消息拉取服务,以及重平衡服务,还有各种定时任务
- 发送心跳到broker
好了,Consumer启动过程就分析到这里,接下来就分析下消费过程。
限于作者个人水平,文中难免有错误之处,欢迎指正! 勿喷,感谢