在生产者Producer中，通过sendMessageInTransaction()方法发送事务消息，这里先向Broker发送一条预处理消息，sendMessageInTransaction()方法中，传入了需要发送的事务消息跟实现了LocalTransactionExecuter接口的tranExecutor实例跟参数，在其中的executeLocalTransactionBranch方法中实现具体的事务操作。我们先来看下DefaultMQProducerImpl中的sendMessageInTransaction()方法
public TransactionSendResult sendMessageInTransaction(final Message msg,
final LocalTransactionExecuter tranExecuter, final Object arg)
throws MQClientException {
if (null == tranExecuter) {
throw new MQClientException("tranExecutor is null", null);
}
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 {
sendResult = this.send(msg);
} catch (Exception e) {
throw new MQClientException("send message Exception", e);
}
LocalTransactionState localTransactionState = LocalTransactionState.UNKNOW;
Throwable localException = null;
switch (sendResult.getSendStatus()) {
case SEND_OK: {
try {
if (sendResult.getTransactionId() != null) {
msg.putUserProperty("__transactionId__", sendResult.getTransactionId());
}
localTransactionState = tranExecuter.executeLocalTransactionBranch(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;
}
try {
this.endTransaction(sendResult, localTransactionState, localException);
} catch (Exception e) {
log.warn("local transaction execute " + localTransactionState + ", but end broker transaction failed", e);
}
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;
}第一次发送消息前，先检查发送的消息的参数，再将消息的事务属性设为transactuion_prepared属性，然后设置消息的生产者组名，其他与普通消息发送流程一样。
发送至Broker，进行消息存储，在commitLog中方式都是一样，我们具体看到doDispatch中的两个dispatch方法。
class CommitLogDispatcherBuildConsumeQueue implements CommitLogDispatcher {
@Override
public void dispatch(DispatchRequest request) {
final int tranType = MessageSysFlag.getTransactionValue(request.getSysFlag());
switch (tranType) {
case MessageSysFlag.TRANSACTION_NOT_TYPE:
case MessageSysFlag.TRANSACTION_COMMIT_TYPE:
DefaultMessageStore.this.putMessagePositionInfo(request);
break;
case MessageSysFlag.TRANSACTION_PREPARED_TYPE:
case MessageSysFlag.TRANSACTION_ROLLBACK_TYPE:
break;
}
}
}这里可以看到transaction_prepared是直接返回了，并未创建LogicConsumerQueue索引。也就是说处于preparedType的事务消息并不会将消息的具体存储位置分发到消费队列，该消息并不会被消费者通消费队列以及消费队列上的偏移量取到并消费。
class CommitLogDispatcherBuildIndex implements CommitLogDispatcher {
@Override
public void dispatch(DispatchRequest request) {
if (DefaultMessageStore.this.messageStoreConfig.isMessageIndexEnable()) {
DefaultMessageStore.this.indexService.buildIndex(request);
}
}
}switch (tranType) {
case MessageSysFlag.TRANSACTION_NOT_TYPE:
case MessageSysFlag.TRANSACTION_PREPARED_TYPE:
case MessageSysFlag.TRANSACTION_COMMIT_TYPE:
break;
case MessageSysFlag.TRANSACTION_ROLLBACK_TYPE:
return;
}
可以看到这里添加了index文件索引，如果是transaction_rollback类型的话，直接返回，不创建index文件索引。
如果第一次消息发送成功，那么会调用tranExecutor的executeLocalTransactionBranch()传入消息跟参数，完成后调用endTransaction()方法，进行消息的二次提交。
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());
}
String transactionId = sendResult.getTransactionId();
final String brokerAddr = this.mQClientFactory.findBrokerAddressInPublish(sendResult.getMessageQueue().getBrokerName());
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());
String remark = localException != null ? ("executeLocalTransactionBranch exception: " + localException.toString()) : null;
this.mQClientFactory.getMQClientAPIImpl().endTransactionOneway(brokerAddr, requestHeader, remark,
this.defaultMQProducer.getSendMsgTimeout());
}
我们可以看到这里的requestHeader是EndTransactionRequestHeader的实例，再根据事务executeLocalTransactionBranch的结果，设置其事务属性为commit/rollback，再调用MQClientAPIImpl的OneWay方式二次发送消息。
我们看到broker端接收到后的具体逻辑处理。EndTransactionProcessor的processRequest()方法
@Override
public RemotingCommand processRequest(ChannelHandlerContext ctx,
RemotingCommand request) throws RemotingCommandException {
final RemotingCommand response = RemotingCommand.createResponseCommand(null);
final EndTransactionRequestHeader requestHeader =
(EndTransactionRequestHeader) request.decodeCommandCustomHeader(EndTransactionRequestHeader.class);
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;
}
}
final MessageExt msgExt = this.brokerController.getMessageStore().lookMessageByOffset(requestHeader.getCommitLogOffset());
if (msgExt != null) {
final String pgroupRead = msgExt.getProperty(MessageConst.PROPERTY_PRODUCER_GROUP);
if (!pgroupRead.equals(requestHeader.getProducerGroup())) {
response.setCode(ResponseCode.SYSTEM_ERROR);
response.setRemark("the producer group wrong");
return response;
}
if (msgExt.getQueueOffset() != requestHeader.getTranStateTableOffset()) {
response.setCode(ResponseCode.SYSTEM_ERROR);
response.setRemark("the transaction state table offset wrong");
return response;
}
if (msgExt.getCommitLogOffset() != requestHeader.getCommitLogOffset()) {
response.setCode(ResponseCode.SYSTEM_ERROR);
response.setRemark("the commit log offset wrong");
return response;
}
MessageExtBrokerInner msgInner = this.endMessageTransaction(msgExt);
msgInner.setSysFlag(MessageSysFlag.resetTransactionValue(msgInner.getSysFlag(), requestHeader.getCommitOrRollback()));
msgInner.setQueueOffset(requestHeader.getTranStateTableOffset());
msgInner.setPreparedTransactionOffset(requestHeader.getCommitLogOffset());
msgInner.setStoreTimestamp(msgExt.getStoreTimestamp());
if (MessageSysFlag.TRANSACTION_ROLLBACK_TYPE == requestHeader.getCommitOrRollback()) {
msgInner.setBody(null);
}
final MessageStore messageStore = this.brokerController.getMessageStore();
final PutMessageResult putMessageResult = messageStore.putMessage(msgInner);
if (putMessageResult != null) {
switch (putMessageResult.getPutMessageStatus()) {
// Success
case PUT_OK:
case FLUSH_DISK_TIMEOUT:
case FLUSH_SLAVE_TIMEOUT:
case SLAVE_NOT_AVAILABLE:
response.setCode(ResponseCode.SUCCESS);
response.setRemark(null);
break;
// Failed
case CREATE_MAPEDFILE_FAILED:
response.setCode(ResponseCode.SYSTEM_ERROR);
response.setRemark("create mapped file failed.");
break;
case MESSAGE_ILLEGAL:
case PROPERTIES_SIZE_EXCEEDED:
response.setCode(ResponseCode.MESSAGE_ILLEGAL);
response.setRemark("the message is illegal, maybe msg body or properties length not matched. msg body length limit 128k, msg properties length limit 32k.");
break;
case SERVICE_NOT_AVAILABLE:
response.setCode(ResponseCode.SERVICE_NOT_AVAILABLE);
response.setRemark("service not available now.");
break;
case OS_PAGECACHE_BUSY:
response.setCode(ResponseCode.SYSTEM_ERROR);
response.setRemark("OS page cache busy, please try another machine");
break;
case UNKNOWN_ERROR:
response.setCode(ResponseCode.SYSTEM_ERROR);
response.setRemark("UNKNOWN_ERROR");
break;
default:
response.setCode(ResponseCode.SYSTEM_ERROR);
response.setRemark("UNKNOWN_ERROR DEFAULT");
break;
}
return response;
} else {
response.setCode(ResponseCode.SYSTEM_ERROR);
response.setRemark("store putMessage return null");
}
} else {
response.setCode(ResponseCode.SYSTEM_ERROR);
response.setRemark("find prepared transaction message failed");
return response;
}
return response;
}
方法实现很长，先解析请求request，如果是commt或rollback类型，那么继续处理，否则错误类型直接返回。
接下来，会根据第一次提交的消息的commitLogOffset取得存储在commitLog上第一次消息提交的实体。如果先后两次消息的生产者组名/事务偏移量/存储偏移量不同则设置错误response，并返回错误response。如果正确，那么判断其是否是rollBack类型，如果是那么设其得到的消息实体的body为null，且调用messageStore，将第一次存储的消息覆盖为null。
如果为commit类型，那么按照正常流程调用messageStore，将第一次存储的消息覆盖，建立索引，提供给消费者可正常索引消息进行操作。
生产者的事务消息二阶段提交流程基本就是这样。