一、案例
public class TransactionProducer {
public static void main(String[] args) throws MQClientException, InterruptedException {
// 事务监听器
TransactionListener transactionListener = new TransactionListenerImpl();
// 创建生产者来发送事务消息
TransactionMQProducer producer = new TransactionMQProducer("please_rename_unique_group_name");
// 检查事务的线程池
ExecutorService executorService = new ThreadPoolExecutor(2, 5, 100, TimeUnit.SECONDS, new ArrayBlockingQueue<Runnable>(2000), new ThreadFactory() {
@Override
public Thread newThread(Runnable r) {
Thread thread = new Thread(r);
thread.setName("client-transaction-msg-check-thread");
return thread;
}
});
// 设置检查事务线程池
producer.setExecutorService(executorService);
// 设置事务监听器
producer.setTransactionListener(transactionListener);
producer.start();
String[] tags = new String[] {"TagA", "TagB", "TagC", "TagD", "TagE"};
for (int i = 0; i < 10; i++) {
try {
// 创建消息
Message msg =
new Message("TopicTest1234", tags[i % tags.length], "KEY" + i,
("Hello RocketMQ " + i).getBytes(RemotingHelper.DEFAULT_CHARSET));
// 发送消息
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();
}
}
- 创建事务监听器，用来执行事务，以及检查事务执行的结果；事务监听器需要实现TransactionListener接口
public class TransactionListenerImpl implements TransactionListener {
private AtomicInteger transactionIndex = new AtomicInteger(0);
private ConcurrentHashMap<String, Integer> localTrans = new ConcurrentHashMap<>();
// 当发送事务准备(half)消息成功时，将调用此方法执行本地事务
@Override
public LocalTransactionState executeLocalTransaction(Message msg, Object arg) {
int value = transactionIndex.getAndIncrement();
int status = value % 3;
localTrans.put(msg.getTransactionId(), status);
return LocalTransactionState.UNKNOW;
}
// 当没有回应准备(半)消息，代理将发送检查消息来检查事务状态，并执行此操作
// 方法被调用以获取事务状态
@Override
public LocalTransactionState checkLocalTransaction(MessageExt msg) {
Integer status = 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;
}
}
- 创建的线程池是用来执行TransactionListenerImpl#checkLocalTransaction
二、发送事务消息
TransactionMQProducer#sendMessageInTransaction
@Override
public TransactionSendResult sendMessageInTransaction(final Message msg,
final Object arg) throws MQClientException {
if (null == this.transactionListener) {
throw new MQClientException("TransactionListener is null", null);
}
msg.setTopic(NamespaceUtil.wrapNamespace(this.getNamespace(), msg.getTopic()));
return this.defaultMQProducerImpl.sendMessageInTransaction(msg, null, arg);
}
TransactionMQProducer#sendMessageInTransaction
public TransactionSendResult sendMessageInTransaction(final Message msg,
final LocalTransactionExecuter localTransactionExecuter, final Object arg)
throws MQClientException {
TransactionListener transactionListener = getCheckListener();
if (null == localTransactionExecuter && null == transactionListener) {
throw new MQClientException("tranExecutor is null", null);
}
// ignore DelayTimeLevel parameter
if (msg.getDelayTimeLevel() != 0) {
MessageAccessor.clearProperty(msg, MessageConst.PROPERTY_DELAY_TIME_LEVEL);
}
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());
}
String transactionId = msg.getProperty(MessageConst.PROPERTY_UNIQ_CLIENT_MESSAGE_ID_KEYIDX);
if (null != transactionId && !"".equals(transactionId)) {
msg.setTransactionId(transactionId);
}
if (null != localTransactionExecuter) {
localTransactionState = localTransactionExecuter.executeLocalTransactionBranch(msg, arg);
} else if (transactionListener != null) {
log.debug("Used new transaction API");
localTransactionState = transactionListener.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;
}
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;
}
- this.send(msg)，给broker发送消息，其中
MessageAccessor.putProperty(msg, MessageConst.PROPERTY_TRANSACTION_PREPARED, "true")
告诉broker是事务消息，这时候，该消息不能被消费者消费
- 消息发送成功后，开始执行事务
localTransactionState = transactionListener.executeLocalTransaction(msg, arg);
- 事务执行完后，向broker发送事务执行结果，若执行成功，消费者可以执行该事务消息；若执行失败，消费者不能消费该事务消息
三、发送事务执行结果
DefaultMQProducerImpl#endTransaction
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());
}
四、总结
- 事务消息一开始并不是直接发送到指定的那个topic 对应的队列里面的，而是发送到RMQ_SYS_TRANS_HALF_TOPIC topic里面，防止消费者消费；然后broker响应生产者，执行executeLocalTransaction 方法来执行本地事务
- 当本地事务执行成功，返回 commit提交事务，broker会先从RMQ_SYS_TRANS_HALF_TOPIC topic里面找到消息，恢复原来的样子，存储到生产者设置的topic；存储成功之后生成一条删除消息 并放到RMQ_SYS_TRANS_OP_HALF_TOPIC topic 里面
- 如果本地事务失败，就要rollback ，会从RMQ_SYS_TRANS_HALF_TOPIC topic里面找到你那个消息，生成一条删除消息放到RMQ_SYS_TRANS_OP_HALF_TOPIC topic 里面
五、异常情况处理
1、提交信息失败
提交消息失败，直接抛异常，不用执行事务
2、事务执行完后，向broker提交事务执行结果失败
broker 会有个事务服务线程，隔一段时间就扫描RMQ_SYS_TRANS_HALF_TOPIC topic 里面没有提交或者回滚的消息，然后它发送消息给生产者，生产者执行检查事务的方法TransactionListener#checkLocalTransaction，询问事务的执行状态，默认访问15次
