seata源码分析之全局事务的开启跟xid的传递
概览
首先我们通过@GlobalTransactional这个注解开启一个全局事务，而GlobalTransactionScanner.wrapIfNecessary()会为所有方法上加了这个注解的bean注入一个包装了GlobalTransactionalInterceptor实例的advisor，然后返回一个代理对象。GlobalTransactionalInterceptor会在该bean的方法调用前进行拦截，判断是否开启全局事务
上源码，关键位置我打了注释
@Override
protected Object wrapIfNecessary(Object bean, String beanName, Object cacheKey) {
//判断全局事务是否启用
if (disableGlobalTransaction) {
return bean;
}
try {
synchronized (PROXYED_SET) {
if (PROXYED_SET.contains(beanName)) {
return bean;
}
interceptor = null;
//check TCC proxy
if (TCCBeanParserUtils.isTccAutoProxy(bean, beanName, applicationContext)) {
//TCC interceptor, proxy bean of sofa:reference/dubbo:reference, and LocalTCC
interceptor = new TccActionInterceptor(TCCBeanParserUtils.getRemotingDesc(beanName));
} else {
Class serviceInterface = SpringProxyUtils.findTargetClass(bean);
Class[] interfacesIfJdk = SpringProxyUtils.findInterfaces(bean);
//判断bean里的方法上有没有@GlobalTransactional注解
if (!existsAnnotation(new Class[]{serviceInterface})
&& !existsAnnotation(interfacesIfJdk)) {
return bean;
}
if (interceptor == null) {
//初始化Interceptor,后面会注入代理对象
interceptor = new GlobalTransactionalInterceptor(failureHandlerHook);
ConfigurationFactory.getInstance().addConfigListener(ConfigurationKeys.DISABLE_GLOBAL_TRANSACTION, (ConfigurationChangeListener) interceptor);
}
}
//判断当前bean是否已被aop代理过，比如说方法上加了@Transactional就会被spring代理
//如果没有被代理，调用父类的模板方法进行代理，advisor通过被重写的
//getAdvicesAndAdvisorsForBean返回上面的interceptor进行包装
if (!AopUtils.isAopProxy(bean)) {
bean = super.wrapIfNecessary(bean, beanName, cacheKey);
} else {
AdvisedSupport advised = SpringProxyUtils.getAdvisedSupport(bean);
//把GlobalTransactionalInterceptor包装成advisor
Advisor[] advisor = buildAdvisors(beanName, getAdvicesAndAdvisorsForBean(null, null, null));
for (Advisor avr : advisor) {
advised.addAdvisor(0, avr);
}
}
PROXYED_SET.add(beanName);
return bean;
}
} catch (Exception exx) {
throw new RuntimeException(exx);
}
}
@Override
protected Object[] getAdvicesAndAdvisorsForBean(Class beanClass, String beanName,
TargetSource customTargetSource) throws BeansException {
//返回interceptor[]
return new Object[]{interceptor};
}
@Override
public void afterPropertiesSet() {
if (disableGlobalTransaction) {
if (LOGGER.isInfoEnabled()) {
LOGGER.info("Global transaction is disabled.");
}
return;
}
//使用netty初始化seata client，建立到server端的连接
initClient();
}这里可以看出来，只要我们在方法上加了@GlobalTranscational注解，对应的bean就会被seata进行代理，同时重写了afterPropertiesSet，在bean初始化完毕后会进行调用，这个client就是用来跟server端通信的，包括后面会说到的下游服务的事务提交与回滚都与这个有关
GlobalTransactionalInterceptor重写了MethodInterceptor的invoke()方法，在spring执行通知代理对象的通知方法时，最终会调用到这个invoke()
@Override
public Object invoke(final MethodInvocation methodInvocation) throws Throwable {
Class targetClass = methodInvocation.getThis() != null ?AopUtils.getTargetClass(methodInvocation.getThis()) : null;
Method specificMethod = ClassUtils.getMostSpecificMethod(methodInvocation.getMethod(), targetClass);
final Method method = BridgeMethodResolver.findBridgedMethod(specificMethod);
final GlobalTransactional globalTransactionalAnnotation = getAnnotation(method, GlobalTransactional.class);
final GlobalLock globalLockAnnotation = getAnnotation(method, GlobalLock.class);
//如果全局事务可用并且方法上加了@GlobalTransactional注解
if (!disable && globalTransactionalAnnotation != null) {
//处理全局事务
return handleGlobalTransaction(methodInvocation, globalTransactionalAnnotation);
} else if (!disable && globalLockAnnotation != null) {
return handleGlobalLock(methodInvocation);
} else {
return methodInvocation.proceed();
}
}这里就会然后调用handleGlobalTransaction(methodInvocation, globalTransactionalAnnotation);
private Object handleGlobalTransaction(final MethodInvocation methodInvocation,
final GlobalTransactional globalTrxAnno) throws Throwable {
try {
return transactionalTemplate.execute(new TransactionalExecutor() {
@Override
public Object execute() throws Throwable {
return methodInvocation.proceed();
}
public String name() {
String name = globalTrxAnno.name();
if (!StringUtils.isNullOrEmpty(name)) {
return name;
}
return formatMethod(methodInvocation.getMethod());
}
@Override
public TransactionInfo getTransactionInfo() {
TransactionInfo transactionInfo = new TransactionInfo();
transactionInfo.setTimeOut(globalTrxAnno.timeoutMills());
transactionInfo.setName(name());
transactionInfo.setPropagation(globalTrxAnno.propagation());
Set rollbackRules = new LinkedHashSet<>();
for (Class rbRule : globalTrxAnno.rollbackFor()) {
rollbackRules.add(new RollbackRule(rbRule));
}
for (String rbRule : globalTrxAnno.rollbackForClassName()) {
rollbackRules.add(new RollbackRule(rbRule));
}
for (Class rbRule : globalTrxAnno.noRollbackFor()) {
rollbackRules.add(new NoRollbackRule(rbRule));
}
for (String rbRule : globalTrxAnno.noRollbackForClassName()) {
rollbackRules.add(new NoRollbackRule(rbRule));
}
transactionInfo.setRollbackRules(rollbackRules);
return transactionInfo;
}
});
} catch (TransactionalExecutor.ExecutionException e) {
TransactionalExecutor.Code code = e.getCode();
switch (code) {
case RollbackDone:
throw e.getOriginalException();
case BeginFailure:
failureHandler.onBeginFailure(e.getTransaction(), e.getCause());
throw e.getCause();
case CommitFailure:
failureHandler.onCommitFailure(e.getTransaction(), e.getCause());
throw e.getCause();
case RollbackFailure:
failureHandler.onRollbackFailure(e.getTransaction(), e.getCause());
throw e.getCause();
case RollbackRetrying:
failureHandler.onRollbackRetrying(e.getTransaction(), e.getCause());
throw e.getCause();
default:
throw new ShouldNeverHappenException(String.format("Unknown TransactionalExecutor.Code: %s", code));
}
}
} 这里transactionalTemplate.execute（）传入了一个匿名实现，其execute()就是放行让后续的通知方法继续执行，这个我们不关心，进入transactionalTemplate.execute（）
public Object execute(TransactionalExecutor business) throws Throwable {
// 1 get transactionInfo
TransactionInfo txInfo = business.getTransactionInfo();
if (txInfo == null) {
throw new ShouldNeverHappenException("transactionInfo does not exist");
}
// 1.1 get or create a transaction
GlobalTransaction tx = GlobalTransactionContext.getCurrentOrCreate();
// 1.2 Handle the Transaction propatation and the branchType
Propagation propagation = txInfo.getPropagation();
SuspendedResourcesHolder suspendedResourcesHolder = null;
try {
switch (propagation) {
case NOT_SUPPORTED:
suspendedResourcesHolder = tx.suspend(true);
return business.execute();
case REQUIRES_NEW:
suspendedResourcesHolder = tx.suspend(true);
break;
case SUPPORTS:
if (!existingTransaction()) {
return business.execute();
}
break;
case REQUIRED:
break;
case NEVER:
if (existingTransaction()) {
throw new TransactionException(
String.format("Existing transaction found for transaction marked with propagation 'never',xid = %s"
,RootContext.getXID()));
} else {
return business.execute();
}
case MANDATORY:
if (!existingTransaction()) {
throw new TransactionException("No existing transaction found for transaction marked with propagation 'mandatory'");
}
break;
default:
throw new TransactionException("Not Supported Propagation:" + propagation);
}
try {
// 2. begin transaction
beginTransaction(txInfo, tx);
Object rs = null;
try {
// Do Your Business
rs = business.execute();
} catch (Throwable ex) {
// 3.the needed business exception to rollback.
completeTransactionAfterThrowing(txInfo, tx, ex);
throw ex;
}
// 4. everything is fine, commit.
commitTransaction(tx);
return rs;
} finally {
//5. clear
triggerAfterCompletion();
cleanUp();
}
} finally {
tx.resume(suspendedResourcesHolder);
}
}这里首先初始化一个GlobalTransaction实例tx，用于保存后续生成的xid跟事务状态等一些属性。然后对事务的传播属性做了些校验。然后我们进入beginTransaction(txInfo, tx);顾名思义，这里快要到核心了
private void beginTransaction(TransactionInfo txInfo, GlobalTransaction tx) throws TransactionalExecutor.ExecutionException {
try {
//执行hook的begin()方法做一些额外处理
triggerBeforeBegin();
tx.begin(txInfo.getTimeOut(), txInfo.getName());
triggerAfterBegin();
} catch (TransactionException txe) {
throw new TransactionalExecutor.ExecutionException(tx, txe,
TransactionalExecutor.Code.BeginFailure);
}
}这里的trigger方法执行我们通过TransactionHookManager.registerHook()注册的一些hook方法，如果我们要在事务开始前后做一些事情，就可以通过这种方式。
进入tx.begin()
@Override
public void begin(int timeout, String name) throws TransactionException {
if (role != GlobalTransactionRole.Launcher) {
assertXIDNotNull();
if (LOGGER.isDebugEnabled()) {
LOGGER.debug("Ignore Begin(): just involved in global transaction [{}]", xid);
}
return;
}
assertXIDNull();
if (RootContext.getXID() != null) {
throw new IllegalStateException();
}
//开启事务并拿到xid
xid = transactionManager.begin(null, null, name, timeout);
//设置事务状态
status = GlobalStatus.Begin;
//xid跟当前线程做全局绑定
RootContext.bind(xid);
if (LOGGER.isInfoEnabled()) {
LOGGER.info("Begin new global transaction [{}]", xid);
}
}继续到 transactionManager.begin
@Override
public String begin(String applicationId, String transactionServiceGroup, String name, int timeout)
throws TransactionException {
GlobalBeginRequest request = new GlobalBeginRequest();
request.setTransactionName(name);
request.setTimeout(timeout);
//通知seata-server开启全局事务，并拿到全局事务id(xid)
GlobalBeginResponse response = (GlobalBeginResponse)syncCall(request);
if (response.getResultCode() == ResultCode.Failed) {
throw new TmTransactionException(TransactionExceptionCode.BeginFailed, response.getMsg());
}
return response.getXid();
}最后我们就开启了一个全局事务，那么我们的xid是怎么向下游传递的呢，看看对feign的集成是怎么做的？SeataFeignClient.execute
@Override
public Response execute(Request request, Request.Options options) throws IOException {
//设置xid
Request modifiedRequest = getModifyRequest(request);
//调用下游服务
return this.delegate.execute(modifiedRequest, options);
}
private Request getModifyRequest(Request request) {
String xid = RootContext.getXID();
if (StringUtils.isEmpty(xid)) {
return request;
}
Map> headers = new HashMap<>(MAP_SIZE);
//设置xid到消息头
headers.putAll(request.headers());
List seataXid = new ArrayList<>();
seataXid.add(xid);
headers.put(RootContext.KEY_XID, seataXid);
return Request.create(request.method(), request.url(), headers, request.body(),
request.charset());
} 这里用SeataFeignClient替换了默认的feignClient，把xid放到了requestHeader里。那么下游又是怎么拿的呢？SeataHandlerInterceptor.preHandle()
@Override
public boolean preHandle(HttpServletRequest request, HttpServletResponse response,
Object handler) {
String xid = RootContext.getXID();
//从消息头中获取xid
String rpcXid = request.getHeader(RootContext.KEY_XID);
if (log.isDebugEnabled()) {
log.debug("xid in RootContext {} xid in RpcContext {}", xid, rpcXid);
}
if (xid == null && rpcXid != null) {
RootContext.bind(rpcXid);
if (log.isDebugEnabled()) {
log.debug("bind {} to RootContext", rpcXid);
}
}
return true;
}这里SeataHandlerInterceptor实现了HandlerInterceptor，springMVC会在Controller方法调用之前拿到所有注册到容器中的拦截器链去执行其preHandle()方法，具体可参考DispatcherServlet.doDispatch()。
好了，到这里就大概把seata的全局事务的开启以及xid的传递捋了一遍，后面会聊聊seata跟hystrix做集成时常见的一些坑