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二十一、RocketMQ源码分析之RocketMQ事务消息实现原理上篇

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文章永久连接:https://tech.souyunku.com/?p=6041

作者:唯有坚持不懈 | 出处:https://blog.csdn.net/prestigeding/article/details/78888290


根据上节Demo示例,发送事务消息的入口为:TransactionMQProducer#sendMessageInTransaction:

public TransactionSendResult sendMessageInTransaction(final Message msg, final Object arg) throws MQClientException {
        if (null == this.transactionListener) {    // @1
            throw new MQClientException("TransactionListener is null", null);
        }

        return this.defaultMQProducerImpl.sendMessageInTransaction(msg, transactionListener, arg);  // @2
    }

   代码@1:如果transactionListener为空,则直接抛出异常。
   代码@2:调用defaultMQProducerImpl的sendMessageInTransaction方法。
   DefaultMQProducerImpl#sendMessageInTransaction

public TransactionSendResult sendMessageInTransaction(final Message msg,
           final TransactionListener tranExecuter, final Object arg)  throws MQClientException {

   Step1:首先先阐述一下参数含义。final Message msg:消息;TransactionListener tranExecuter:事务监听器; Object arg:其他附加参数,该参数会再TransactionListener 回调函数中原值传入。
   DefaultMQProducerImpl#sendMessageInTransaction

SendResult sendResult = null;
MessageAccessor.putProperty(msg, MessageConst.PROPERTY_TRANSACTION_PREPARED, "true");
MessageAccessor.putProperty(msg, MessageConst.PROPERTY_PRODUCER_GROUP, this.defaultMQProducer.getProducerGroup());
try {
       sendResult = this.send(msg);
} catch (Exception e) {
       throw new MQClientException("send message Exception", e);
}

   Step2:在消息属性中,添加两个属性:TRAN_MSG,其值为true,表示为事务消息;PGROUP:消息所属发送者组,然后以同步方式发送消息。
   在消息发送之前,会先检查消息的属性TRAN_MSG,如果存在并且值为true,则通过设置消息系统标记的方式,设置消息为MessageSysFlag.TRANSACTION_PREPARED_TYPE。
   DefaultMQProducerImpl#sendKernelImpl

final String tranMsg = msg.getProperty(MessageConst.PROPERTY_TRANSACTION_PREPARED);
if (tranMsg != null && Boolean.parseBoolean(tranMsg)) {
       sysFlag |= MessageSysFlag.TRANSACTION_PREPARED_TYPE;
}

SendMessageProcessor#sendMessage
String traFlag = oriProps.get(MessageConst.PROPERTY_TRANSACTION_PREPARED);
if (traFlag != null && Boolean.parseBoolean(traFlag)) {
        if (this.brokerController.getBrokerConfig().isRejectTransactionMessage()) {
             response.setCode(ResponseCode.NO_PERMISSION);
             response.setRemark(
                    "the broker[" + this.brokerController.getBrokerConfig().getBrokerIP1()
                        + "] sending transaction message is forbidden");
             return response;
       }
      putMessageResult = this.brokerController.getTransactionalMessageService().prepareMessage(msgInner);
} else {
      putMessageResult = this.brokerController.getMessageStore().putMessage(msgInner);
}

   Step3:Broker端首先客户发送消息请求后,判断消息类型,如果是事务消息,则调用TransactionalMessageService#prepareMessage方法,否则走原先的逻辑,调用MessageStore#putMessage方法。

org.apache.rocketmq.broker.transaction.queue.TransactionalMessageServiceImpl#prepareMessage
public PutMessageResult prepareMessage(MessageExtBrokerInner messageInner) {
        return transactionalMessageBridge.putHalfMessage(messageInner);
 }

   step4:事务消息,将调用TransactionalMessageServiceImpl#prepareMessage方法,继而调用TransactionalMessageBridge#prepareMessage方法。

TransactionalMessageBridge#parseHalfMessageInner
public PutMessageResult putHalfMessage(MessageExtBrokerInner messageInner) {
        return store.putMessage(parseHalfMessageInner(messageInner));
    }

    private MessageExtBrokerInner parseHalfMessageInner(MessageExtBrokerInner msgInner) {
        MessageAccessor.putProperty(msgInner, MessageConst.PROPERTY_REAL_TOPIC, msgInner.getTopic());
        MessageAccessor.putProperty(msgInner, MessageConst.PROPERTY_REAL_QUEUE_ID,
            String.valueOf(msgInner.getQueueId()));
        msgInner.setSysFlag(
            MessageSysFlag.resetTransactionValue(msgInner.getSysFlag(), MessageSysFlag.TRANSACTION_NOT_TYPE));
        msgInner.setTopic(TransactionalMessageUtil.buildHalfTopic());
        msgInner.setQueueId(0);
        msgInner.setPropertiesString(MessageDecoder.messageProperties2String(msgInner.getProperties()));
        return msgInner;
    }

   Step5:备份消息的原主题名称与原队列ID,然后取消是事务消息的消息标签,重新设置消息的主题为:RMQ_SYS_TRANS_HALF_TOPIC,队列ID固定为0。然后调用MessageStore#putMessage方法将消息持久化,这里TransactionalMessageBridge桥接类,就是封装事务消息的相关流程,最终调用MessageStore完成消息的持久化。消息入库后,会继续回到DefaultMQProducerImpl#sendMessageInTransaction,上文的Step2后面,也就是通过同步将消息发送到消息服务端。
   DefaultMQProducerImpl#sendMessageInTransaction

switch (sendResult.getSendStatus()) {
            case SEND_OK: {
                try {
                    if (sendResult.getTransactionId() != null) {
                        msg.putUserProperty("__transactionId__", sendResult.getTransactionId());
                    }
                    String transactionId = msg.getProperty(MessageConst.PROPERTY_UNIQ_CLIENT_MESSAGE_ID_KEYIDX);
                    if (null != transactionId && !"".equals(transactionId)) {
                        msg.setTransactionId(transactionId);
                    }
                    localTransactionState = tranExecuter.executeLocalTransaction(msg, arg);
                    if (null == localTransactionState) {
                        localTransactionState = LocalTransactionState.UNKNOW;
                    }

                    if (localTransactionState != LocalTransactionState.COMMIT_MESSAGE) {
                        log.info("executeLocalTransactionBranch return {}", localTransactionState);
                        log.info(msg.toString());
                    }
                } catch (Throwable e) {
                    log.info("executeLocalTransactionBranch exception", e);
                    log.info(msg.toString());
                    localException = e;
                }
            }
            break;
            case FLUSH_DISK_TIMEOUT:
            case FLUSH_SLAVE_TIMEOUT:
            case SLAVE_NOT_AVAILABLE:
                localTransactionState = LocalTransactionState.ROLLBACK_MESSAGE;
                break;
            default:
                break;
        }

   Step6:如果消息发送成功,会回调TransactionListener#executeLocalTransaction方法,执行本地事务,并且返回本地事务状态为:public enum LocalTransactionState {COMMIT_MESSAGE,ROLLBACK_MESSAGE,
UNKNOW,} 之一,注意:TransactionListener#executeLocalTransaction是在发送者成功发送PREPARED消息后,会执行本地事务方法,然后返回本地事务状态;如果PREPARED消息发送失败,则不会调用
TransactionListener#executeLocalTransaction,并且本地事务消息,设置为
LocalTransactionState.ROLLBACK_MESSAGE,表示消息需要被回滚。
   DefaultMQProducerImpl#sendMessageInTransaction

try {
this.endTransaction(sendResult, localTransactionState, localException);
} catch (Exception e) {
log.warn("local transaction execute " + localTransactionState + ", but end broker transaction failed", e);
}

   step7:调用endTransaction方法结束事务(提交或回滚)。
   DefaultMQProducerImpl#endTransaction

EndTransactionRequestHeader requestHeader = new EndTransactionRequestHeader();
requestHeader.setTransactionId(transactionId);
requestHeader.setCommitLogOffset(id.getOffset());
switch (localTransactionState) {
    case COMMIT_MESSAGE:
         requestHeader.setCommitOrRollback(MessageSysFlag.TRANSACTION_COMMIT_TYPE);
         break;
    case ROLLBACK_MESSAGE:
         requestHeader.setCommitOrRollback(MessageSysFlag.TRANSACTION_ROLLBACK_TYPE);
         break;
     case UNKNOW:
         requestHeader.setCommitOrRollback(MessageSysFlag.TRANSACTION_NOT_TYPE);
         break;
     default:
         break;
}
requestHeader.setProducerGroup(this.defaultMQProducer.getProducerGroup());
requestHeader.setTranStateTableOffset(sendResult.getQueueOffset());
requestHeader.setMsgId(sendResult.getMsgId());

   step8:组装结束事务请求,主要参数为:事务ID、事务操作(commitOrRollback)、消费组、消息队列偏移量、消息ID,fromTransactionCheck,从这里发出的请求,默认为false。Broker端的请求处理器为:EndTransactionProcessor。
   step9:EndTransactionProcessor根据事务提交类型:TRANSACTION_COMMIT_TYPE(提交事务)、TRANSACTION_ROLLBACK_TYPE(回滚事务)、TRANSACTION_NOT_TYPE、忽略该请求,会记录info级别的日志相关的代码将在下文详细分析,在这里,我们先大概梳理一条消息发送的路径TransactionMQProducer#sendMessageInTransaction的调用链来总结一下事务消息的发送流程。
img_0914_01_1.png
   本文到这里,初步展示了事务消息的发送流程,总的说来,RocketMQ的事务消息发送使用二阶段提交思路,首先,在消息发送时,先发送消息类型为Prepread类型的消息,然后在将该消息成功存入到消息服务器后,会回调   TransactionListener#executeLocalTransaction,执行本地事务状态回调函数,然后根据该方法的返回值,结束事务:
   1、COMMIT_MESSAGE :提交事务。
   2、ROLLBACK_MESSAGE:回滚事务。
   3、UNKNOW:未知事务状态,此时消息服务器(Broker)收到EndTransaction命令时,将不对这种消息做处理,消息还处于Prepared类型,存储在主题为:RMQ_SYS_TRANS_HALF_TOPIC的队列中,然后消息发送流程将结束,那这些消息如何提交或回滚呢?为了实现避免客户端需要再次发送提交、回滚命令,RocketMQ会采取定时任务将RMQ_SYS_TRANS_HALF_TOPIC中的消息取出,然后回到客户端,判断该消息是否需要提交或回滚,来完成事务消息的声明周期,该部分内容将在下节重点探讨。

   事务消息后续文章预告:
   1、事务消息状态会查机制实现。
   2、消息服务端在收到客户端的回滚、提交命令时,如果高效处理事务消息的提交、回滚动作。
   3、事务消息实战。


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