Seata 是一款开源的分布式事务解决方案，致力于提供高性能和简单易用的分布式事务服务。
Seata 将为用户提供了 AT、TCC、SAGA 和 XA 事务模式，为用户打造一站式的分布式解决方案。
1、SeataAutoConfiguration
在该核心类中主要创建事务管理器之 GlobalTransactionScanner 实例 & 资源管理器 SeataAutoDataSourceProxyCreator。
@ComponentScan(basePackages = "io.seata.spring.boot.autoconfigure.properties")
@ConditionalOnProperty(prefix = StarterConstants.SEATA_PREFIX, name = "enabled", havingValue = "true", matchIfMissing = true)
@Configuration
@EnableConfigurationProperties({
SeataProperties.class})
public class SeataAutoConfiguration {
private static final Logger LOGGER = LoggerFactory.getLogger(SeataAutoConfiguration.class);
@Bean(BEAN_NAME_SPRING_APPLICATION_CONTEXT_PROVIDER)
@ConditionalOnMissingBean(name = {
BEAN_NAME_SPRING_APPLICATION_CONTEXT_PROVIDER})
public SpringApplicationContextProvider springApplicationContextProvider() {
return new SpringApplicationContextProvider();
}
@Bean(BEAN_NAME_FAILURE_HANDLER)
@ConditionalOnMissingBean(FailureHandler.class)
public FailureHandler failureHandler() {
return new DefaultFailureHandlerImpl();
}
@Bean
@DependsOn({
BEAN_NAME_SPRING_APPLICATION_CONTEXT_PROVIDER, BEAN_NAME_FAILURE_HANDLER})
@ConditionalOnMissingBean(GlobalTransactionScanner.class)
public GlobalTransactionScanner globalTransactionScanner(SeataProperties seataProperties, FailureHandler failureHandler) {
if (LOGGER.isInfoEnabled()) {
LOGGER.info("Automatically configure Seata");
}
return new GlobalTransactionScanner(seataProperties.getApplicationId(), seataProperties.getTxServiceGroup(), failureHandler);
}
@Bean(BEAN_NAME_SEATA_AUTO_DATA_SOURCE_PROXY_CREATOR)
@ConditionalOnProperty(prefix = StarterConstants.SEATA_PREFIX, name = {
"enableAutoDataSourceProxy", "enable-auto-data-source-proxy"}, havingValue = "true", matchIfMissing = true)
@ConditionalOnMissingBean(SeataAutoDataSourceProxyCreator.class)
public SeataAutoDataSourceProxyCreator seataAutoDataSourceProxyCreator(SeataProperties seataProperties) {
return new SeataAutoDataSourceProxyCreator(seataProperties.isUseJdkProxy(),seataProperties.getExcludesForAutoProxying());
}
}
2、GlobalTransactionScanner
GlobalTransactionScanner实现了BeanPostProcessor子类之AbstractAutoProxyCreator。核心方法wrapIfNecessary在BeanPostProcessor之postProcessAfterInitialization方法调用中完成回调。
protected Object wrapIfNecessary(Object bean, String beanName, Object cacheKey) {
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);
if (!existsAnnotation(new Class[]{
serviceInterface})
&& !existsAnnotation(interfacesIfJdk)) {
// 判断是否存在GlobalTransactional、GlobalLock注解
return bean;
}
interceptor = new GlobalTransactionalInterceptor(failureHandlerHook);
}
if (!AopUtils.isAopProxy(bean)) {
bean = super.wrapIfNecessary(bean, beanName, cacheKey);//调用spring AOP代理
} else {
AdvisedSupport advised = SpringProxyUtils.getAdvisedSupport(bean);
Advisor[] advisor = buildAdvisors(beanName, getAdvicesAndAdvisorsForBean(null, null, null));
for (Advisor avr : advisor) {
advised.addAdvisor(0, avr);
}
}
PROXYED_SET.add(beanName);
return bean;
}
}
}
bean：方法存在GlobalTransactional、GlobalLock注解的目标类。
3、GlobalTransactionalInterceptor
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);
if (specificMethod != null && !specificMethod.getDeclaringClass().equals(Object.class)) {
final Method method = BridgeMethodResolver.findBridgedMethod(specificMethod);
final GlobalTransactional globalTransactionalAnnotation =
getAnnotation(method, targetClass, GlobalTransactional.class);
final GlobalLock globalLockAnnotation = getAnnotation(method, targetClass, GlobalLock.class);
boolean localDisable = disable || (degradeCheck && degradeNum >= degradeCheckAllowTimes);
if (!localDisable) {
if (globalTransactionalAnnotation != null) {
return handleGlobalTransaction(methodInvocation, globalTransactionalAnnotation);
} else if (globalLockAnnotation != null) {
return handleGlobalLock(methodInvocation);
}
}
}
return methodInvocation.proceed();
}
private Object handleGlobalTransaction(final MethodInvocation methodInvocation,
final GlobalTransactional globalTrxAnno) throws Throwable {
boolean succeed = true;
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<RollbackRule> 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:
succeed = false;
failureHandler.onBeginFailure(e.getTransaction(), e.getCause());
throw e.getCause();
case CommitFailure:
succeed = false;
failureHandler.onCommitFailure(e.getTransaction(), e.getCause());
throw e.getCause();
case RollbackFailure:
failureHandler.onRollbackFailure(e.getTransaction(), e.getOriginalException());
throw e.getOriginalException();
case RollbackRetrying:
failureHandler.onRollbackRetrying(e.getTransaction(), e.getOriginalException());
throw e.getOriginalException();
default:
throw new ShouldNeverHappenException(String.format("Unknown TransactionalExecutor.Code: %s", code));
}
} finally {
if (degradeCheck) {
EVENT_BUS.post(new DegradeCheckEvent(succeed));
}
}
}
3.1、TransactionalTemplate
public Object execute(TransactionalExecutor business) throws Throwable {
// 1 get transactionInfo 注解存在事务的相关信息
TransactionInfo txInfo = business.getTransactionInfo();
// 1.1 get or create a transaction DefaultGlobalTransaction
GlobalTransaction tx = GlobalTransactionContext.getCurrentOrCreate();
// 1.2 Handle the Transaction propatation and the branchType
Propagation propagation = txInfo.getPropagation();
SuspendedResourcesHolder suspendedResourcesHolder = null;
try {
switch (propagation) {
...//事务传播策略
}
try {
triggerBeforeBegin();
// 2. begin transaction
tx.begin(txInfo.getTimeOut(), txInfo.getName());//tx：DefaultGlobalTransaction
triggerAfterBegin();
Object rs = null;
try {
// 3.执行业务代码目标方法
rs = business.execute();
} catch (Throwable ex) {
// 4.the needed business exception to rollback.
completeTransactionAfterThrowing(txInfo, tx, ex);
throw ex;
}
// 5. everything is fine, commit.
commitTransaction(tx);
return rs;
} finally {
//6. clear
triggerAfterCompletion();
cleanUp();
}
} finally {
tx.resume(suspendedResourcesHolder);
}
}
- 步骤2主要是通过Netty实现的RPC框架远程获取分支事务ID【应用服务机器IP:PORT:事务唯一标识ID】。
- 步骤3真正触发业务代码目标方法，执行RM的本地事务。
3.2、DefaultGlobalTransaction获取分布式事务xid
public void begin(int timeout, String name) throws TransactionException {
if (role != GlobalTransactionRole.Launcher) {
...
return;
}
//DefaultTransactionManager
xid = transactionManager.begin(null, null, name, timeout);
status = GlobalStatus.Begin;
RootContext.bind(xid);
}
3.3、DefaultTransactionManager
public String begin(String applicationId, String transactionServiceGroup, String name, int timeout){
GlobalBeginRequest request = new GlobalBeginRequest();
request.setTransactionName(name);
request.setTimeout(timeout);
//rpc调用TC服务中生成的分支事务ID【xid】 由于RM分布式部署所以存在负载均衡策略
GlobalBeginResponse response = (GlobalBeginResponse) syncCall(request);
return response.getXid();
}
GlobalLock注解说明
从执行过程和提交过程可以看出，既然开启全局事务 @GlobalTransactional注解可以在事务提交前，查询全局锁是否存在，那为什么 Seata 还要设计多处一个 @GlobalLock注解呢?
因为并不是所有的数据库操作都需要开启全局事务，而开启全局事务是一个比较重的操作，需要向 TC 发起开启全局事务等 RPC 过程，而@GlobalLock注解只会在执行过程中查询全局锁是否存在，不会去开启全局事务，因此在不需要全局事务，而又需要检查全局锁避免脏读脏写时，使用@GlobalLock注解是一个更加轻量的操作。