这是我的第一篇博客，思来想去，决定以RocketMQ（版本4.3.2） 源码分析开始写写，不定期更新，也可能随时停更。话不多说，直接开始。
从RocketMQ 3.0.8 之后 到 4.3.0 之前，在这期间的版本均不支持分布式事务消息。包括这在期间使用比较广泛的3.2.6 就是不支持分布式事务消息。分布式事务是分布式系统开发中的一个难点，RocketMQ是基于最终一致性的思想实现的。rocketMQ保证本地事务成功时，消息一定会发送成功并被成功消费，如果本地事务失败了，消息就不会被发送。
放一张的官网的事务处理流程图：
事务流程
可以很清晰的看到事务消息的完整流程
首先介绍下上图中提到的2个概念
1.half消息是什么？
half消息指的是暂时无法投递的消息。当消息成功发送到MQ服务器，但服务器没有收到来自生产者的消息的第二次确认时，该消息被标记为“暂时无法投递”。此状态中的消息称为half消息。
2.消息状态回查是什么意思？
由于网络断开或生产者应用程序重新启动可能导致丢失事务消息的第二次确认。当MQ服务器发现消息状态长时间为half消息时，它将向消息生产者发送回查请求，检查生产者上次本地事物的执行结果，以此为基础进行消息的提交或回滚。
上边的图详细描述了rocketMQ中分布式事务的每个阶段，下边用文字描述一下这个过程：
1.生产者向MQ服务器发送half消息。
2.half消息发送成功后，MQ服务器返回确认消息给生产者。
3.生产者开始执行本地事务。
4.根据本地事务执行的结果（UNKNOW、commit、rollback）向MQ Server发送提交或回滚消息。
5.如果错过了（可能因为网络异常、生产者突然宕机等导致的异常情况）提交/回滚消息，则MQ服务器将向同一组中的每个生产者发送回查消息以获取事务状态。
6.回查生产者本地事物状态。
7.生产者根据本地事务状态发送提交/回滚消息。
8.MQ服务器将丢弃回滚的消息，但已提交（进行过二次确认的half消息）的消息将投递给消费者进行消费。
从上述流程可以知道，事务消息其实只是保证了生产者本地事务和发送消息的原子性
消费者在消费事务消息时，broker处理事务消息的消费与普通消息是一样的，若消费不成功，则broker会重复投递该消息16次，若仍然不成功则需要人工介入。
OK，知道了rocketMQ的事物处理流程后，我们根据官网提供的例子跟下源码再看看，源码下载地址：https://github.com/apache/rocketmq
一、生产者发送prepare消息
生产者发送事务消息过程
先看下TransactionListener 的定义：
public interface TransactionListener {
/**
* When send transactional prepare(half) message succeed, this method will be invoked to execute local transaction.
* 一旦生产者发送事务消息成功，会调用这个方法提交本地事务
*
* @param msg Half(prepare) message
* @param arg Custom business parameter
* @return Transaction state
*/
LocalTransactionState executeLocalTransaction(final Message msg, final Object arg);
/**
* When no response to prepare(half) message. broker will send check message to check the transaction status, and this
* method will be invoked to get local transaction status.
* 当prepare发送后超时没有返回，那么MQ服务器会回调执行这个方法用来检查上次本地事务执行的状态
*
* @param msg Check message
* @return Transaction state
*/
LocalTransactionState checkLocalTransaction(final MessageExt msg);
}
TransactionListener的实现类
public class TransactionListenerImpl implements TransactionListener {
private final AtomicInteger transactionIndex = new AtomicInteger(0);
private final ConcurrentHashMap localTrans = new ConcurrentHashMap<>();
@Override
public LocalTransactionState executeLocalTransaction(final Message msg, final Object arg) {
// 提交本地事物 伪代码 提交事务成功成功之后 将状态保存起来 方便事务状态回查
final int value = this.transactionIndex.getAndIncrement();
final int status = value % 3;
this.localTrans.put(msg.getTransactionId(), status);
return LocalTransactionState.UNKNOW;
}
@Override
public LocalTransactionState checkLocalTransaction(final MessageExt msg) {
// 回调检查本地事物 伪代码
final Integer status = this.localTrans.get(msg.getTransactionId());
if (null != status) {
switch (status) {
case 0:
return LocalTransactionState.UNKNOW;
case 1:
return LocalTransactionState.COMMIT_MESSAGE;
case 2:
return LocalTransactionState.ROLLBACK_MESSAGE;
default:
return LocalTransactionState.COMMIT_MESSAGE;
}
}
return LocalTransactionState.COMMIT_MESSAGE;
}
}
在生产者代码中会初始化事务监听对象，并注册到TransactionMQProducer中，下面附上生产者的示例代码
public class TransactionProducer {
public static void main(final String[] args) throws MQClientException, InterruptedException {
// 监听对象
final TransactionListener transactionListener = new TransactionListenerImpl();
// 创建生产者
final TransactionMQProducer producer = new TransactionMQProducer("please_rename_unique_group_name");
// 初始化线程池
final ExecutorService executorService = new ThreadPoolExecutor(2, 5, 100, TimeUnit.SECONDS, new ArrayBlockingQueue(2000), new ThreadFactory() {
@Override
public Thread newThread(final Runnable r) {
final Thread thread = new Thread(r);
thread.setName("client-transaction-msg-check-thread");
return thread;
}
});
producer.setExecutorService(executorService);
// 设置监听
producer.setTransactionListener(transactionListener);
// 启动生产者
producer.start();
final String[] tags = new String[]{"TagA", "TagB", "TagC", "TagD", "TagE"};
for (int i = 0; i < 10; i++) {
try {
final Message msg =
new Message("TopicTest1234", tags[i % tags.length], "KEY" + i,
("Hello RocketMQ " + i).getBytes(RemotingHelper.DEFAULT_CHARSET));
// 发送消息
final SendResult sendResult = producer.sendMessageInTransaction(msg, null);
System.out.printf("%s%n", sendResult);
Thread.sleep(10);
} catch (MQClientException | UnsupportedEncodingException e) {
e.printStackTrace();
}
}
for (int i = 0; i < 100000; i++) {
Thread.sleep(1000);
}
producer.shutdown();
}
}
接下来分析一下消息发送，生产者调用sendMessageInTransaction 方法，进入这个方法
@Override
public TransactionSendResult sendMessageInTransaction(final Message msg,
final Object arg) throws MQClientException {
// transactionListener 对象在生产者代码初始化完毕
if (null == this.transactionListener) {
throw new MQClientException("TransactionListener is null", null);
}
return this.defaultMQProducerImpl.sendMessageInTransaction(msg, null, arg);
}
会继续调用DefaultMQProducerImpl 的sendMessageInTransaction方法，DefaultMQProducerImpl 是DefaultMQProducer的成员变量， 会在 TransactionMQProducer 的父类DefaultMQProducer的构造器中初始化：
/**
* Constructor specifying both producer group and RPC hook.
*
* @param producerGroup Producer group, see the name-sake field.
* @param rpcHook RPC hook to execute per each remoting command execution.
*/
public DefaultMQProducer(final String producerGroup, RPCHook rpcHook) {
this.producerGroup = producerGroup;
defaultMQProducerImpl = new DefaultMQProducerImpl(this, rpcHook);
}
接下来进入DefaultMQProducerImpl 的sendMessageInTransaction方法，这个方法非常重要，实现了事物消息发送的关键逻辑（发送消息->执行本地事物->commit/rollback消息）
public TransactionSendResult sendMessageInTransaction(final Message msg,
final LocalTransactionExecuter localTransactionExecuter, final Object arg)
throws MQClientException {
// 获取注册到 TransactionMQProducer 注册的 TransactionListener 如果没有注册 返回null
final TransactionListener transactionListener = getCheckListener();
if (null == localTransactionExecuter && null == transactionListener) {
throw new MQClientException("tranExecutor is null", null);
}
// 验证消息长度 和 topic
Validators.checkMessage(msg, this.defaultMQProducer);
SendResult sendResult = null;
MessageAccessor.putProperty(msg, MessageConst.PROPERTY_TRANSACTION_PREPARED, "true");
MessageAccessor.putProperty(msg, MessageConst.PROPERTY_PRODUCER_GROUP, this.defaultMQProducer.getProducerGroup());
try {
// 发送half 消息
sendResult = this.send(msg);
} catch (final Exception e) {
throw new MQClientException("send message Exception", e);
}
LocalTransactionState localTransactionState = LocalTransactionState.UNKNOW;
Throwable localException = null;
switch (sendResult.getSendStatus()) {
// half 消息发送成功
case SEND_OK: {
try {
if (sendResult.getTransactionId() != null) {
msg.putUserProperty("__transactionId__", sendResult.getTransactionId());
}
final String transactionId = msg.getProperty(MessageConst.PROPERTY_UNIQ_CLIENT_MESSAGE_ID_KEYIDX);
if (null != transactionId && !"".equals(transactionId)) {
msg.setTransactionId(transactionId);
}
// localTransactionExecutor 传进来为null，这个分支不会走
if (null != localTransactionExecuter) {
localTransactionState = localTransactionExecuter.executeLocalTransactionBranch(msg, arg);
} else if (transactionListener != null) {
this.log.debug("Used new transaction API");
// 提交本地事物
localTransactionState = transactionListener.executeLocalTransaction(msg, arg);
}
// 事务提交状态判定
if (null == localTransactionState) {
localTransactionState = LocalTransactionState.UNKNOW;
}
if (localTransactionState != LocalTransactionState.COMMIT_MESSAGE) {
this.log.info("executeLocalTransactionBranch return {}", localTransactionState);
this.log.info(msg.toString());
}
} catch (final Throwable e) {
this.log.info("executeLocalTransactionBranch exception", e);
this.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;
}
try {
// 根据本地事物提交情况 发送commit or rollback 消息
this.endTransaction(sendResult, localTransactionState, localException);
} catch (final Exception e) {
this.log.warn("local transaction execute " + localTransactionState + ", but end broker transaction failed", e);
}
final TransactionSendResult transactionSendResult = new TransactionSendResult();
transactionSendResult.setSendStatus(sendResult.getSendStatus());
transactionSendResult.setMessageQueue(sendResult.getMessageQueue());
transactionSendResult.setMsgId(sendResult.getMsgId());
transactionSendResult.setQueueOffset(sendResult.getQueueOffset());
transactionSendResult.setTransactionId(sendResult.getTransactionId());
transactionSendResult.setLocalTransactionState(localTransactionState);
return transactionSendResult;
}
进入send() 方法
public SendResult send(
final Message msg) throws MQClientException, RemotingException, MQBrokerException, InterruptedException {
// 默认超时时间是3秒
return send(msg, this.defaultMQProducer.getSendMsgTimeout());
}
public SendResult send(final Message msg,
final long timeout) throws MQClientException, RemotingException, MQBrokerException, InterruptedException {
return this.sendDefaultImpl(msg, CommunicationMode.SYNC, null, timeout);
}
继续调用sendDefaultImpl()方法
private SendResult sendDefaultImpl(
final Message msg,
final CommunicationMode communicationMode,
final SendCallback sendCallback,
final long timeout
) throws MQClientException, RemotingException, MQBrokerException, InterruptedException {
this.makeSureStateOK();
// 验证topic 和消息长度
Validators.checkMessage(msg, this.defaultMQProducer);
final long invokeID = this.random.nextLong();
final long beginTimestampFirst = System.currentTimeMillis();
long beginTimestampPrev = beginTimestampFirst;
long endTimestamp = beginTimestampFirst;
// 如果本地缓存中没有该消息的topic 信息 则会去namesrv 中获取topic 信息 并更新到本地缓存
final TopicPublishInfo topicPublishInfo = this.tryToFindTopicPublishInfo(msg.getTopic());
if (topicPublishInfo != null && topicPublishInfo.ok()) {
boolean callTimeout = false;
MessageQueue mq = null;
Exception exception = null;
SendResult sendResult = null;
// 消息发送重试次数
final int timesTotal = communicationMode == CommunicationMode.SYNC ? 1 + this.defaultMQProducer.getRetryTimesWhenSendFailed() : 1;
int times = 0;
final String[] brokersSent = new String[timesTotal];
for (; times < timesTotal; times++) {
final String lastBrokerName = null == mq ? null : mq.getBrokerName();
final MessageQueue mqSelected = this.selectOneMessageQueue(topicPublishInfo, lastBrokerName);
if (mqSelected != null) {
mq = mqSelected;
brokersSent[times] = mq.getBrokerName();
try {
beginTimestampPrev = System.currentTimeMillis();
final long costTime = beginTimestampPrev - beginTimestampFirst;
if (timeout < costTime) {
callTimeout = true;
break;
}
// 发送消息代码
sendResult = this.sendKernelImpl(msg, mq, communicationMode, sendCallback, topicPublishInfo, timeout - costTime);
endTimestamp = System.currentTimeMillis();
this.updateFaultItem(mq.getBrokerName(), endTimestamp - beginTimestampPrev, false);
switch (communicationMode) {
case ASYNC:
return null;
case ONEWAY:
return null;
case SYNC:
if (sendResult.getSendStatus() != SendStatus.SEND_OK) {
if (this.defaultMQProducer.isRetryAnotherBrokerWhenNotStoreOK()) {
continue;
}
}
return sendResult;
default:
break;
···省略非关键代码
}
}
}
}
}
}
sendKernelImpl()方法中会设置必要属性，并调用getMQClientAPIImpl().sendMessage方法
private SendResult sendKernelImpl(final Message msg,
final MessageQueue mq,
final CommunicationMode communicationMode,
final SendCallback sendCallback,
final TopicPublishInfo topicPublishInfo,
final long timeout) throws MQClientException, RemotingException, MQBrokerException, InterruptedException {
final long beginStartTime = System.currentTimeMillis();
String brokerAddr = this.mQClientFactory.findBrokerAddressInPublish(mq.getBrokerName());
if (null == brokerAddr) {
tryToFindTopicPublishInfo(mq.getTopic());
brokerAddr = this.mQClientFactory.findBrokerAddressInPublish(mq.getBrokerName());
}
SendMessageContext context = null;
if (brokerAddr != null) {
brokerAddr = MixAll.brokerVIPChannel(this.defaultMQProducer.isSendMessageWithVIPChannel(), brokerAddr);
final byte[] prevBody = msg.getBody();
try {
//for MessageBatch,ID has been set in the generating process
if (!(msg instanceof MessageBatch)) {
MessageClientIDSetter.setUniqID(msg);
}
int sysFlag = 0;
boolean msgBodyCompressed = false;
if (this.tryToCompressMessage(msg)) {
sysFlag |= MessageSysFlag.COMPRESSED_FLAG;
msgBodyCompressed = true;
}
final String tranMsg = msg.getProperty(MessageConst.PROPERTY_TRANSACTION_PREPARED);
if (tranMsg != null && Boolean.parseBoolean(tranMsg)) {
sysFlag |= MessageSysFlag.TRANSACTION_PREPARED_TYPE;
}
if (hasCheckForbiddenHook()) {
final CheckForbiddenContext checkForbiddenContext = new CheckForbiddenContext();
checkForbiddenContext.setNameSrvAddr(this.defaultMQProducer.getNamesrvAddr());
checkForbiddenContext.setGroup(this.defaultMQProducer.getProducerGroup());
checkForbiddenContext.setCommunicationMode(communicationMode);
checkForbiddenContext.setBrokerAddr(brokerAddr);
checkForbiddenContext.setMessage(msg);
checkForbiddenContext.setMq(mq);
checkForbiddenContext.setUnitMode(this.isUnitMode());
this.executeCheckForbiddenHook(checkForbiddenContext);
}
if (this.hasSendMessageHook()) {
context = new SendMessageContext();
context.setProducer(this);
context.setProducerGroup(this.defaultMQProducer.getProducerGroup());
context.setCommunicationMode(communicationMode);
context.setBornHost(this.defaultMQProducer.getClientIP());
context.setBrokerAddr(brokerAddr);
context.setMessage(msg);
context.setMq(mq);
final String isTrans = msg.getProperty(MessageConst.PROPERTY_TRANSACTION_PREPARED);
if (isTrans != null && isTrans.equals("true")) {
context.setMsgType(MessageType.Trans_Msg_Half);
}
if (msg.getProperty("__STARTDELIVERTIME") != null || msg.getProperty(MessageConst.PROPERTY_DELAY_TIME_LEVEL) != null) {
context.setMsgType(MessageType.Delay_Msg);
}
this.executeSendMessageHookBefore(context);
}
final SendMessageRequestHeader requestHeader = new SendMessageRequestHeader();
requestHeader.setProducerGroup(this.defaultMQProducer.getProducerGroup());
requestHeader.setTopic(msg.getTopic());
requestHeader.setDefaultTopic(this.defaultMQProducer.getCreateTopicKey());
requestHeader.setDefaultTopicQueueNums(this.defaultMQProducer.getDefaultTopicQueueNums());
requestHeader.setQueueId(mq.getQueueId());
requestHeader.setSysFlag(sysFlag);
requestHeader.setBornTimestamp(System.currentTimeMillis());
requestHeader.setFlag(msg.getFlag());
requestHeader.setProperties(MessageDecoder.messageProperties2String(msg.getProperties()));
requestHeader.setReconsumeTimes(0);
requestHeader.setUnitMode(this.isUnitMode());
requestHeader.setBatch(msg instanceof MessageBatch);
if (requestHeader.getTopic().startsWith(MixAll.RETRY_GROUP_TOPIC_PREFIX)) {
final String reconsumeTimes = MessageAccessor.getReconsumeTime(msg);
if (reconsumeTimes != null) {
requestHeader.setReconsumeTimes(Integer.valueOf(reconsumeTimes));
MessageAccessor.clearProperty(msg, MessageConst.PROPERTY_RECONSUME_TIME);
}
final String maxReconsumeTimes = MessageAccessor.getMaxReconsumeTimes(msg);
if (maxReconsumeTimes != null) {
requestHeader.setMaxReconsumeTimes(Integer.valueOf(maxReconsumeTimes));
MessageAccessor.clearProperty(msg, MessageConst.PROPERTY_MAX_RECONSUME_TIMES);
}
}
SendResult sendResult = null;
switch (communicationMode) {
case ASYNC:
Message tmpMessage = msg;
if (msgBodyCompressed) {
//If msg body was compressed, msgbody should be reset using prevBody.
//Clone new message using commpressed message body and recover origin massage.
//Fix bug:https://github.com/apache/rocketmq-externals/issues/66
tmpMessage = MessageAccessor.cloneMessage(msg);
msg.setBody(prevBody);
}
final long costTimeAsync = System.currentTimeMillis() - beginStartTime;
if (timeout < costTimeAsync) {
throw new RemotingTooMuchRequestException("sendKernelImpl call timeout");
}
sendResult = this.mQClientFactory.getMQClientAPIImpl().sendMessage(
brokerAddr,
mq.getBrokerName(),
tmpMessage,
requestHeader,
timeout - costTimeAsync,
communicationMode,
sendCallback,
topicPublishInfo,
this.mQClientFactory,
this.defaultMQProducer.getRetryTimesWhenSendAsyncFailed(),
context,
this);
break;
case ONEWAY:
case SYNC:
// // 参数为CommunicationMode.SYNC 走这个分支
final long costTimeSync = System.currentTimeMillis() - beginStartTime;
if (timeout < costTimeSync) {
throw new RemotingTooMuchRequestException("sendKernelImpl call timeout");
}
// 发送消息
sendResult = this.mQClientFactory.getMQClientAPIImpl().sendMessage(
brokerAddr,
mq.getBrokerName(),
msg,
requestHeader,
timeout - costTimeSync,
communicationMode,
context,
this);
break;
default:
assert false;
break;
}
}
}
}
我们接着MQClientAPIImpl组件的sendMessage()方法继续往下看，SYNC分支
public SendResult sendMessage(
final String addr,
final String brokerName,
final Message msg,
final SendMessageRequestHeader requestHeader,
final long timeoutMillis,
final CommunicationMode communicationMode,
final SendMessageContext context,
final DefaultMQProducerImpl producer
) throws RemotingException, MQBrokerException, InterruptedException {
return sendMessage(addr, brokerName, msg, requestHeader, timeoutMillis, communicationMode, null, null, null, 0, context, producer);
}
public SendResult sendMessage(
final String addr,
final String brokerName,
final Message msg,
final SendMessageRequestHeader requestHeader,
final long timeoutMillis,
final CommunicationMode communicationMode,
final SendCallback sendCallback,
final TopicPublishInfo topicPublishInfo,
final MQClientInstance instance,
final int retryTimesWhenSendFailed,
final SendMessageContext context,
final DefaultMQProducerImpl producer
) throws RemotingException, MQBrokerException, InterruptedException {
long beginStartTime = System.currentTimeMillis();
RemotingCommand request = null;
if (sendSmartMsg || msg instanceof MessageBatch) {
SendMessageRequestHeaderV2 requestHeaderV2 = SendMessageRequestHeaderV2.createSendMessageRequestHeaderV2(requestHeader);
request = RemotingCommand.createRequestCommand(msg instanceof MessageBatch ? RequestCode.SEND_BATCH_MESSAGE : RequestCode.SEND_MESSAGE_V2, requestHeaderV2);
} else {
request = RemotingCommand.createRequestCommand(RequestCode.SEND_MESSAGE, requestHeader);
}
request.setBody(msg.getBody());
switch (communicationMode) {
case ONEWAY:
this.remotingClient.invokeOneway(addr, request, timeoutMillis);
return null;
case ASYNC:
final AtomicInteger times = new AtomicInteger();
long costTimeAsync = System.currentTimeMillis() - beginStartTime;
if (timeoutMillis < costTimeAsync) {
throw new RemotingTooMuchRequestException("sendMessage call timeout");
}
this.sendMessageAsync(addr, brokerName, msg, timeoutMillis - costTimeAsync, request, sendCallback, topicPublishInfo, instance,
retryTimesWhenSendFailed, times, context, producer);
return null;
case SYNC:
// 判断超时时间
long costTimeSync = System.currentTimeMillis() - beginStartTime;
if (timeoutMillis < costTimeSync) {
throw new RemotingTooMuchRequestException("sendMessage call timeout");
}
// 发送消息
return this.sendMessageSync(addr, brokerName, msg, timeoutMillis - costTimeSync, request);
default:
assert false;
break;
}
return null;
}
sendMessageSync方法，调用NettyRemotingClient组件的invokeSync()方法进行处理
private SendResult sendMessageSync(
final String addr,
final String brokerName,
final Message msg,
final long timeoutMillis,
final RemotingCommand request
) throws RemotingException, MQBrokerException, InterruptedException {
final RemotingCommand response = this.remotingClient.invokeSync(addr, request, timeoutMillis);
assert response != null;
return this.processSendResponse(brokerName, msg, response);
}
invokeSync()方法中会通过nio的方式把消息发送到MQ服务器端broker，invokeSync()方法中会继续调用invokeSyncImpl()方法
@Override
public RemotingCommand invokeSync(String addr, final RemotingCommand request, long timeoutMillis)
throws InterruptedException, RemotingConnectException, RemotingSendRequestException, RemotingTimeoutException {
long beginStartTime = System.currentTimeMillis();
final Channel channel = this.getAndCreateChannel(addr);
if (channel != null && channel.isActive()) {
try {
if (this.rpcHook != null) {
this.rpcHook.doBeforeRequest(addr, request);
}
long costTime = System.currentTimeMillis() - beginStartTime;
if (timeoutMillis < costTime) {
throw new RemotingTimeoutException("invokeSync call timeout");
}
RemotingCommand response = this.invokeSyncImpl(channel, request, timeoutMillis - costTime);
if (this.rpcHook != null) {
this.rpcHook.doAfterResponse(RemotingHelper.parseChannelRemoteAddr(channel), request, response);
}
return response;
} catch (RemotingSendRequestException e) {
log.warn("invokeSync: send request exception, so close the channel[{}]", addr);
this.closeChannel(addr, channel);
throw e;
} catch (RemotingTimeoutException e) {
if (nettyClientConfig.isClientCloseSocketIfTimeout()) {
this.closeChannel(addr, channel);
log.warn("invokeSync: close socket because of timeout, {}ms, {}", timeoutMillis, addr);
}
log.warn("invokeSync: wait response timeout exception, the channel[{}]", addr);
throw e;
}
} else {
this.closeChannel(addr, channel);
throw new RemotingConnectException(addr);
}
}
public RemotingCommand invokeSyncImpl(final Channel channel, final RemotingCommand request,
final long timeoutMillis)
throws InterruptedException, RemotingSendRequestException, RemotingTimeoutException {
final int opaque = request.getOpaque();
try {
final ResponseFuture responseFuture = new ResponseFuture(channel, opaque, timeoutMillis, null, null);
this.responseTable.put(opaque, responseFuture);
final SocketAddress addr = channel.remoteAddress();
// netty
channel.writeAndFlush(request).addListener(new ChannelFutureListener() {
@Override
public void operationComplete(ChannelFuture f) throws Exception {
if (f.isSuccess()) {
responseFuture.setSendRequestOK(true);
return;
} else {
responseFuture.setSendRequestOK(false);
}
responseTable.remove(opaque);
responseFuture.setCause(f.cause());
responseFuture.putResponse(null);
log.warn("send a request command to channel <" + addr + "> failed.");
}
});
RemotingCommand responseCommand = responseFuture.waitResponse(timeoutMillis);
if (null == responseCommand) {
if (responseFuture.isSendRequestOK()) {
throw new RemotingTimeoutException(RemotingHelper.parseSocketAddressAddr(addr), timeoutMillis,
responseFuture.getCause());
} else {
throw new RemotingSendRequestException(RemotingHelper.parseSocketAddressAddr(addr), responseFuture.getCause());
}
}
return responseCommand;
} finally {
this.responseTable.remove(opaque);
}
}
MQ服务器端broker处理完发送过来的消息之后会给生产者DefaultMQProducerImpl一个返回值SendResult。
到这里为止我们执行到事物消息的哪个阶段了呢？
现在我们回到关键流程中去，关键流程就在DefaultMQProducerImpl组件的sendMessageInTransaction()方法中
然后我们发现其实我们刚把这段代码sendResult = this.send(msg)执行完毕并拿到了一个sendResult返回值，这个返回值代表着我们发送这条消息的一个结果（发送成功还是失败）
public TransactionSendResult sendMessageInTransaction(final Message msg,
final LocalTransactionExecuter localTransactionExecuter, final Object arg)
throws MQClientException {
// 获取注册到 TransactionMQProducer 注册的 TransactionListener 如果没有注册 返回null
final TransactionListener transactionListener = getCheckListener();
if (null == localTransactionExecuter && null == transactionListener) {
throw new MQClientException("tranExecutor is null", null);
}
// 验证消息长度 和 topic
Validators.checkMessage(msg, this.defaultMQProducer);
SendResult sendResult = null;
···省略
try {
// 发送half 消息
sendResult = this.send(msg);
} catch (final Exception e) {
throw new MQClientException("send message Exception", e);
}
}
接下来会根据sendResult返回值来执行不同的逻辑处理
如果sendResult为SEND_OK，即发送prepare消息成功，那么就开始执行本地事物（即TransactionListenerImpl组件的executeLocalTransaction()方法）
本地事物返回值是一个枚举localTransactionState(有3种取值 COMMIT_MESSAGE , ROLLBACK_MESSAGE , UNKNOW)
如果发送prepare消息失败，则直接设置localTransactionState的值为ROLLBACK_MESSAGE。最后执行endTransaction()方法进行prepare消息的二次确认。源码如下，这段源码上面也放上去了
public TransactionSendResult sendMessageInTransaction(final Message msg,
final LocalTransactionExecuter localTransactionExecuter, final Object arg)
throws MQClientException {
// 获取注册到 TransactionMQProducer 注册的 TransactionListener 如果没有注册 返回null
final TransactionListener transactionListener = getCheckListener();
if (null == localTransactionExecuter && null == transactionListener) {
throw new MQClientException("tranExecutor is null", null);
}
// 验证消息长度 和 topic
Validators.checkMessage(msg, this.defaultMQProducer);
SendResult sendResult = null;
MessageAccessor.putProperty(msg, MessageConst.PROPERTY_TRANSACTION_PREPARED, "true");
MessageAccessor.putProperty(msg, MessageConst.PROPERTY_PRODUCER_GROUP, this.defaultMQProducer.getProducerGroup());
try {
// 发送half 消息
sendResult = this.send(msg);
} catch (final Exception e) {
throw new MQClientException("send message Exception", e);
}
LocalTransactionState localTransactionState = LocalTransactionState.UNKNOW;
Throwable localException = null;
switch (sendResult.getSendStatus()) {
// half 消息发送成功
case SEND_OK: {
try {
if (sendResult.getTransactionId() != null) {
msg.putUserProperty("__transactionId__", sendResult.getTransactionId());
}
final String transactionId = msg.getProperty(MessageConst.PROPERTY_UNIQ_CLIENT_MESSAGE_ID_KEYIDX);
if (null != transactionId && !"".equals(transactionId)) {
msg.setTransactionId(transactionId);
}
// localTransactionExecutor 传进来为null，这个分支不会走
if (null != localTransactionExecuter) {
localTransactionState = localTransactionExecuter.executeLocalTransactionBranch(msg, arg);
} else if (transactionListener != null) {
this.log.debug("Used new transaction API");
// 提交本地事物
localTransactionState = transactionListener.executeLocalTransaction(msg, arg);
}
// 事务提交状态判定
if (null == localTransactionState) {
localTransactionState = LocalTransactionState.UNKNOW;
}
if (localTransactionState != LocalTransactionState.COMMIT_MESSAGE) {
this.log.info("executeLocalTransactionBranch return {}", localTransactionState);
this.log.info(msg.toString());
}
} catch (final Throwable e) {
this.log.info("executeLocalTransactionBranch exception", e);
this.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;
}
try {
// 根据本地事物提交情况 发送commit or rollback 消息
this.endTransaction(sendResult, localTransactionState, localException);
} catch (final Exception e) {
this.log.warn("local transaction execute " + localTransactionState + ", but end broker transaction failed", e);
}
final TransactionSendResult transactionSendResult = new TransactionSendResult();
transactionSendResult.setSendStatus(sendResult.getSendStatus());
transactionSendResult.setMessageQueue(sendResult.getMessageQueue());
transactionSendResult.setMsgId(sendResult.getMsgId());
transactionSendResult.setQueueOffset(sendResult.getQueueOffset());
transactionSendResult.setTransactionId(sendResult.getTransactionId());
transactionSendResult.setLocalTransactionState(localTransactionState);
return transactionSendResult;
}
看下endTransaction()方法
public void endTransaction(
final SendResult sendResult,
final LocalTransactionState localTransactionState,
final Throwable localException) throws RemotingException, MQBrokerException, InterruptedException, UnknownHostException {
final MessageId id;
if (sendResult.getOffsetMsgId() != null) {
id = MessageDecoder.decodeMessageId(sendResult.getOffsetMsgId());
} else {
id = MessageDecoder.decodeMessageId(sendResult.getMsgId());
}
final String transactionId = sendResult.getTransactionId();
final String brokerAddr = this.mQClientFactory.findBrokerAddressInPublish(sendResult.getMessageQueue().getBrokerName());
final EndTransactionRequestHeader requestHeader = new EndTransactionRequestHeader();
requestHeader.setTransactionId(transactionId);
requestHeader.setCommitLogOffset(id.getOffset());
//根据本地事务执行的结果去设置请求头信息commitOrRollback
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());
final String remark = localException != null ? ("executeLocalTransactionBranch exception: " + localException.toString()) : null;
this.mQClientFactory.getMQClientAPIImpl().endTransactionOneway(brokerAddr, requestHeader, remark,
this.defaultMQProducer.getSendMsgTimeout());
}
public void endTransactionOneway(
final String addr,
final EndTransactionRequestHeader requestHeader,
final String remark,
final long timeoutMillis
) throws RemotingException, MQBrokerException, InterruptedException {
final RemotingCommand request = RemotingCommand.createRequestCommand(RequestCode.END_TRANSACTION, requestHeader);
request.setRemark(remark);
//将request写入channel中，通过socket把消息发送给消费端，后边主要是netty的事儿了
this.remotingClient.invokeOneway(addr, request, timeoutMillis);
}
public void invokeOneway(String addr, RemotingCommand request, long timeoutMillis) throws InterruptedException,
RemotingConnectException, RemotingTooMuchRequestException, RemotingTimeoutException, RemotingSendRequestException {
final Channel channel = this.getAndCreateChannel(addr);
if (channel != null && channel.isActive()) {
try {
if (this.rpcHook != null) {
this.rpcHook.doBeforeRequest(addr, request);
}
this.invokeOnewayImpl(channel, request, timeoutMillis);
} catch (RemotingSendRequestException e) {
log.warn("invokeOneway: send request exception, so close the channel[{}]", addr);
this.closeChannel(addr, channel);
throw e;
}
} else {
this.closeChannel(addr, channel);
throw new RemotingConnectException(addr);
}
}
最终调用NettyRemotingClient组件的invokeOneway()方法完成prepare消息的二次确认，如果localTransactionState的值为COMMIT_MESSAGE时则MQ服务端会将消息投递给消费者进行消费；
但是如果localTransactionState的值为ROLLBACK_MESSAGE时则MQ服务端会删除已经存储的prepare消息，此时消费者将没有机会消费到这条消息。
二、Broker端对消息的处理
（1）Broker处理prepare消息
最终调用SendMessageProcessor组件的sendMessage方法处理事务消息，代码如下
private RemotingCommand sendMessage(final ChannelHandlerContext ctx,
final RemotingCommand request,
final SendMessageContext sendMessageContext,
final SendMessageRequestHeader requestHeader) throws RemotingCommandException {
final RemotingCommand response = RemotingCommand.createResponseCommand(SendMessageResponseHeader.class);
final SendMessageResponseHeader responseHeader = (SendMessageResponseHeader) response.readCustomHeader();
response.setOpaque(request.getOpaque());
response.addExtField(MessageConst.PROPERTY_MSG_REGION, this.brokerController.getBrokerConfig().getRegionId());
response.addExtField(MessageConst.PROPERTY_TRACE_SWITCH, String.valueOf(this.brokerController.getBrokerConfig().isTraceOn()));
log.debug("receive SendMessage request command, {}", request);
final long startTimstamp = this.brokerController.getBrokerConfig().getStartAcceptSendRequestTimeStamp();
if (this.brokerController.getMessageStore().now() < startTimstamp) {
response.setCode(ResponseCode.SYSTEM_ERROR);
response.setRemark(String.format("broker unable to service, until %s", UtilAll.timeMillisToHumanString2(startTimstamp)));
return response;
}
response.setCode(-1);
super.msgCheck(ctx, requestHeader, response);
if (response.getCode() != -1) {
return response;
}
final byte[] body = request.getBody();
int queueIdInt = requestHeader.getQueueId();
final TopicConfig topicConfig = this.brokerController.getTopicConfigManager().selectTopicConfig(requestHeader.getTopic());
if (queueIdInt < 0) {
queueIdInt = Math.abs(this.random.nextInt() % 99999999) % topicConfig.getWriteQueueNums();
}
final MessageExtBrokerInner msgInner = new MessageExtBrokerInner();
msgInner.setTopic(requestHeader.getTopic());
msgInner.setQueueId(queueIdInt);
if (!handleRetryAndDLQ(requestHeader, response, request, msgInner, topicConfig)) {
return response;
}
msgInner.setBody(body);
msgInner.setFlag(requestHeader.getFlag());
MessageAccessor.setProperties(msgInner, MessageDecoder.string2messageProperties(requestHeader.getProperties()));
msgInner.setPropertiesString(requestHeader.getProperties());
msgInner.setBornTimestamp(requestHeader.getBornTimestamp());
msgInner.setBornHost(ctx.channel().remoteAddress());
msgInner.setStoreHost(this.getStoreHost());
msgInner.setReconsumeTimes(requestHeader.getReconsumeTimes() == null ? 0 : requestHeader.getReconsumeTimes());
PutMessageResult putMessageResult = null;
final Map oriProps = MessageDecoder.string2messageProperties(requestHeader.getProperties());
//判断是否是事务消息 如果是事务消息则用事务消息的逻辑处理
final 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;
}
// 处理prepare消息
putMessageResult = this.brokerController.getTransactionalMessageService().prepareMessage(msgInner);
} else {
putMessageResult = this.brokerController.getMessageStore().putMessage(msgInner);
}
return handlePutMessageResult(putMessageResult, response, request, msgInner, responseHeader, sendMessageContext, ctx, queueIdInt);
}
TransactionalMessageService的prepareMessage()方法
public PutMessageResult prepareMessage(MessageExtBrokerInner messageInner) {
return transactionalMessageBridge.putHalfMessage(messageInner);
}
TransactionalMessageBridge的putHalfMessage()方法进行调用保存方法
public PutMessageResult putHalfMessage(MessageExtBrokerInner messageInner) {
return store.putMessage(parseHalfMessageInner(messageInner));
}
(2)Broker处理prepare消息的二次确认，即结束事务消息的处理
2.1 会判断本次事务的最终状态，如果是Commit就改变事物消息状态，使消费者可见，此时消费者就可以消费消息了
2.2 如果是Rollback，那么就删除在broker端存储的事物消息，此时消费者就永远消费不到这条消息
public RemotingCommand processRequest(final ChannelHandlerContext ctx, final RemotingCommand request) throws
RemotingCommandException {
final RemotingCommand response = RemotingCommand.createResponseCommand(null);
final EndTransactionRequestHeader requestHeader =
(EndTransactionRequestHeader) request.decodeCommandCustomHeader(EndTransactionRequestHeader.class);
LOGGER.info("Transaction request:{}", requestHeader);
if (BrokerRole.SLAVE == this.brokerController.getMessageStoreConfig().getBrokerRole()) {
response.setCode(ResponseCode.SLAVE_NOT_AVAILABLE);
LOGGER.warn("Message store is slave mode, so end transaction is forbidden. ");
return response;
}
if (requestHeader.getFromTransactionCheck()) {
switch (requestHeader.getCommitOrRollback()) {
case MessageSysFlag.TRANSACTION_NOT_TYPE: {
LOGGER.warn("Check producer[{}] transaction state, but it's pending status."
+ "RequestHeader: {} Remark: {}",
RemotingHelper.parseChannelRemoteAddr(ctx.channel()),
requestHeader.toString(),
request.getRemark());
return null;
}
case MessageSysFlag.TRANSACTION_COMMIT_TYPE: {
LOGGER.warn("Check producer[{}] transaction state, the producer commit the message."
+ "RequestHeader: {} Remark: {}",
RemotingHelper.parseChannelRemoteAddr(ctx.channel()),
requestHeader.toString(),
request.getRemark());
break;
}
case MessageSysFlag.TRANSACTION_ROLLBACK_TYPE: {
LOGGER.warn("Check producer[{}] transaction state, the producer rollback the message."
+ "RequestHeader: {} Remark: {}",
RemotingHelper.parseChannelRemoteAddr(ctx.channel()),
requestHeader.toString(),
request.getRemark());
break;
}
default:
return null;
}
} else {
switch (requestHeader.getCommitOrRollback()) {
case MessageSysFlag.TRANSACTION_NOT_TYPE: {
LOGGER.warn("The producer[{}] end transaction in sending message, and it's pending status."
+ "RequestHeader: {} Remark: {}",
RemotingHelper.parseChannelRemoteAddr(ctx.channel()),
requestHeader.toString(),
request.getRemark());
return null;
}
case MessageSysFlag.TRANSACTION_COMMIT_TYPE: {
break;
}
case MessageSysFlag.TRANSACTION_ROLLBACK_TYPE: {
LOGGER.warn("The producer[{}] end transaction in sending message, rollback the message."
+ "RequestHeader: {} Remark: {}",
RemotingHelper.parseChannelRemoteAddr(ctx.channel()),
requestHeader.toString(),
request.getRemark());
break;
}
default:
return null;
}
}
OperationResult result = new OperationResult();
// 如果收到的是Commit事务消息
if (MessageSysFlag.TRANSACTION_COMMIT_TYPE == requestHeader.getCommitOrRollback()) {
// 从commitLog中查出原始的prepared消息
// 这要求了Producer在发送最终的Commit消息的时候一定要指定是同一个Broker
result = this.brokerController.getTransactionalMessageService().commitMessage(requestHeader);
if (result.getResponseCode() == ResponseCode.SUCCESS) {
// 检查获取到的消息是否和当前消息匹配
final RemotingCommand res = checkPrepareMessage(result.getPrepareMessage(), requestHeader);
if (res.getCode() == ResponseCode.SUCCESS) {
// 使用原始的prepared消息属性，构建最终发给consumer的消息
final MessageExtBrokerInner msgInner = endMessageTransaction(result.getPrepareMessage());
msgInner.setSysFlag(MessageSysFlag.resetTransactionValue(msgInner.getSysFlag(), requestHeader.getCommitOrRollback()));
msgInner.setQueueOffset(requestHeader.getTranStateTableOffset());
msgInner.setPreparedTransactionOffset(requestHeader.getCommitLogOffset());
msgInner.setStoreTimestamp(result.getPrepareMessage().getStoreTimestamp());
// 调用MessageStore的消息存储接口提交消息，使用真正的topic和queueId
final RemotingCommand sendResult = sendFinalMessage(msgInner);
if (sendResult.getCode() == ResponseCode.SUCCESS) {
// 设置Prepared消息的标记位为delete
this.brokerController.getTransactionalMessageService().deletePrepareMessage(result.getPrepareMessage());
}
return sendResult;
}
return res;
}
} else if (MessageSysFlag.TRANSACTION_ROLLBACK_TYPE == requestHeader.getCommitOrRollback()) {
// 如果收到的是Rollback事务消息
result = this.brokerController.getTransactionalMessageService().rollbackMessage(requestHeader);
if (result.getResponseCode() == ResponseCode.SUCCESS) {
final RemotingCommand res = checkPrepareMessage(result.getPrepareMessage(), requestHeader);
if (res.getCode() == ResponseCode.SUCCESS) {
// 设置Prepared消息的标记位为delete
this.brokerController.getTransactionalMessageService().deletePrepareMessage(result.getPrepareMessage());
}
return res;
}
}
response.setCode(result.getResponseCode());
response.setRemark(result.getResponseRemark());
return response;
}
消息Commit/Rollback后，理论上需要将原来的Prepared消息删除，这样Broker就能知道哪些消息一直没收到Commit/Rollback，需要去Producer回查状态。但是如果直接修改CommitLog文件，这个代价是很大的，所以RocketMQ是通过生成一个新的delete消息来标记的。这样，Broker在检查的时候只需要看下Prepared消息有没有对应的delete消息就可以了，我们看看这个这个操作：
public boolean deletePrepareMessage(MessageExt msgExt) {
// 删除标志
if (this.transactionalMessageBridge.putOpMessage(msgExt, TransactionalMessageUtil.REMOVETAG)) {
log.info("Transaction op message write successfully. messageId={}, queueId={} msgExt:{}", msgExt.getMsgId(), msgExt.getQueueId(), msgExt);
return true;
} else {
log.error("Transaction op message write failed. messageId is {}, queueId is {}", msgExt.getMsgId(), msgExt.getQueueId());
return false;
}
}
三、事务消息是如何处理回查的？
broker在启动时会启动线程回查的服务，在TransactionMessageCheckService的run方法中，该方法会执行到onWaitEnd方法：
public void run() {
log.info("Start transaction check service thread!");
final long checkInterval = this.brokerController.getBrokerConfig().getTransactionCheckInterval();
while (!this.isStopped()) {
this.waitForRunning(checkInterval);
}
log.info("End transaction check service thread!");
}
protected void waitForRunning(long interval) {
if (hasNotified.compareAndSet(true, false)) {
this.onWaitEnd();
return;
}
//entry to wait
waitPoint.reset();
try {
waitPoint.await(interval, TimeUnit.MILLISECONDS);
} catch (InterruptedException e) {
log.error("Interrupted", e);
} finally {
hasNotified.set(false);
this.onWaitEnd();
}
}
protected void onWaitEnd() {
// 超时时间
final long timeout = this.brokerController.getBrokerConfig().getTransactionTimeOut();
// 最大检查次数
final int checkMax = this.brokerController.getBrokerConfig().getTransactionCheckMax();
// 当前时间
final long begin = System.currentTimeMillis();
log.info("Begin to check prepare message, begin time:{}", begin);
// 开始检查
this.brokerController.getTransactionalMessageService().check(timeout, checkMax, this.brokerController.getTransactionalMessageCheckListener());
log.info("End to check prepare message, consumed time:{}", System.currentTimeMillis() - begin);
}
通过netty传递消息最终调用到TransactionListenerImpl组件的checkLocalTransaction()方法来检查本地事物的状态
四、总结
本篇文章从生产者发送prepare消息、Broker端对消息的处理以及事务消息是如何处理回查的3个阶段详细分析了rocketMQ的源码，按照上述代码执行顺序大家完全可以跟着走读下源码。