Seata源码（八）Seata事务生命周期hook

Java极客  |  作者  /  铿然一叶
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如何编写软件设计文档 Seata源码（一）初始化 Seata源码（二）事务基础对象 Seata源码（三）事务处理类结构和流程 Seata源码（四）全局锁GlobalLock Seata源码（五）Seata数据库操作 Seata源码（六）Seata的undo日志操作 Seata源码（七）Seata事务故障处理

1. hook概述

   Seata提供给了事务处理hook，在事务的生命周期过程中可以扩展处理逻辑。事务hook，可由开发者定制实现，相关类结构如下:

   

TransactionHook接口的方法都没有传入参数，只能通过线程变量获取相关数据，例如： RootContext.getXID()

此接口可能在实际使用中还有扩展空间，应允许传入一些需要的参数，否则能做的事情有限。

2. hook注册和获取

   2.1 注册

   直接调用TransactionHookManager的静态方法registerHook完成注册

           // 线程变量, scope为当前线程
       private static final ThreadLocal LOCAL_HOOKS = new ThreadLocal();
   
       public static void registerHook(TransactionHook transactionHook) {
           if (transactionHook == null) {
               throw new NullPointerException("transactionHook must not be null");
           }
           List transactionHooks = LOCAL_HOOKS.get();
           if (transactionHooks == null) {
               LOCAL_HOOKS.set(new ArrayList());
           }
           LOCAL_HOOKS.get().add(transactionHook);
       }
   

   2.2 获取

   TransactionHookManager.java

       public static List getHooks() throws IllegalStateException {
       List hooks = LOCAL_HOOKS.get();
   
       if (hooks == null || hooks.isEmpty()) {
           return Collections.emptyList();
       }
       return Collections.unmodifiableList(hooks);
   }
   

3. hook调用点

   3.1 beforeBegin和beforeBegin

   TransactionalTemplate.java

       private void beginTransaction(TransactionInfo txInfo, GlobalTransaction tx) throws TransactionalExecutor.ExecutionException {
       try {
           // TransactionHook.beforeBegin();
           triggerBeforeBegin();
           tx.begin(txInfo.getTimeOut(), txInfo.getName());
           // TransactionHook.afterBegin();
           triggerAfterBegin();
       } catch (TransactionException txe) {
           throw new TransactionalExecutor.ExecutionException(tx, txe,
               TransactionalExecutor.Code.BeginFailure);
   
       }
   }
   
   private void triggerBeforeBegin() {
       for (TransactionHook hook : getCurrentHooks()) {
           try {
               hook.beforeBegin();
           } catch (Exception e) {
               LOGGER.error("Failed execute beforeBegin in hook {}", e.getMessage(), e);
           }
       }
   }
   
   private void triggerAfterBegin() {
       for (TransactionHook hook : getCurrentHooks()) {
           try {
               hook.afterBegin();
           } catch (Exception e) {
               LOGGER.error("Failed execute afterBegin in hook {}", e.getMessage(), e);
           }
       }
   }
   

   3.2 beforeCommit和afterCommit

   TransactionalTemplate.java

       private void commitTransaction(GlobalTransaction tx) throws TransactionalExecutor.ExecutionException {
       try {
           triggerBeforeCommit();
           tx.commit();
           triggerAfterCommit();
       } catch (TransactionException txe) {
           // 4.1 Failed to commit
           throw new TransactionalExecutor.ExecutionException(tx, txe,
               TransactionalExecutor.Code.CommitFailure);
       }
   }
   

   triggerBeforeCommi和triggerAfterCommit方法调用逻辑同前。

   3.3 beforeRollback和afterRollback

   TransactionalTemplate.java

       private void rollbackTransaction(GlobalTransaction tx, Throwable originalException) throws TransactionException, TransactionalExecutor.ExecutionException {
       triggerBeforeRollback();
       tx.rollback();
       triggerAfterRollback();
       // 3.1 Successfully rolled back
       throw new TransactionalExecutor.ExecutionException(tx, GlobalStatus.RollbackRetrying.equals(tx.getLocalStatus())
           ? TransactionalExecutor.Code.RollbackRetrying : TransactionalExecutor.Code.RollbackDone, originalException);
   }
   

   triggerBeforeRollback和triggerAfterRollback方法调用逻辑同前。

   3.4 afterCompletion

   TransactionalTemplate.java 在所有操作执行完成后finally块中执行。

       public Object execute(TransactionalExecutor business) throws Throwable {
           // 此处省略XXXX行
           } finally {
               //5. clear
               resumeGlobalLockConfig(previousConfig);
               triggerAfterCompletion();
               cleanUp();
           }
   

end.