多线程事务如何回滚？

背景介绍

1，最近有一个大数据量插入的操作入库的业务场景，需要先做一些其他修改操作，然后在执行插入操作，由于插入数据可能会很多，用到多线程去拆分数据并行处理来提高响应时间，如果有一个线程执行失败，则全部回滚。

2，在spring中可以使用@Transactional注解去控制事务，使出现异常时会进行回滚，在多线程中，这个注解则不会生效，如果主线程需要先执行一些修改数据库的操作，当子线程在进行处理出现异常时，主线程修改的数据则不会回滚，导致数据错误。

3，下面用一个简单示例演示多线程事务。

公用的类和方法

/*** 平均拆分list方法.* @param source* @param n* @param <T>* @return*/
public static <T> List<List<T>> averageAssign(List<T> source,int n){List<List<T>> result=new ArrayList<List<T>>();int remaider=source.size()%n; int number=source.size()/n; int offset=0;//偏移量for(int i=0;i<n;i++){List<T> value=null;if(remaider>0){value=source.subList(i*number+offset, (i+1)*number+offset+1);remaider--;offset++;}else{value=source.subList(i*number+offset, (i+1)*number+offset);}result.add(value);}return result;
}
/**  线程池配置* @version V1.0*/
public class ExecutorConfig {private static int maxPoolSize = Runtime.getRuntime().availableProcessors();private volatile static ExecutorService executorService;public static ExecutorService getThreadPool() {if (executorService == null){synchronized (ExecutorConfig.class){if (executorService == null){executorService =  newThreadPool();}}}return executorService;}private static  ExecutorService newThreadPool(){int queueSize = 500;int corePool = Math.min(5, maxPoolSize);return new ThreadPoolExecutor(corePool, maxPoolSize, 10000L, TimeUnit.MILLISECONDS,new LinkedBlockingQueue<>(queueSize),new ThreadPoolExecutor.AbortPolicy());}private ExecutorConfig(){}
}
/** 获取sqlSession* @author 86182* @version V1.0*/
@Component
public class SqlContext {@Resourceprivate SqlSessionTemplate sqlSessionTemplate;public SqlSession getSqlSession(){SqlSessionFactory sqlSessionFactory = sqlSessionTemplate.getSqlSessionFactory();return sqlSessionFactory.openSession();}

示例事务不成功操作

/*** 测试多线程事务.* @param employeeDOList*/
@Override
@Transactional
public void saveThread(List<EmployeeDO> employeeDOList) {try {//先做删除操作,如果子线程出现异常,此操作不会回滚this.getBaseMapper().delete(null);//获取线程池ExecutorService service = ExecutorConfig.getThreadPool();//拆分数据,拆分5份List<List<EmployeeDO>> lists=averageAssign(employeeDOList, 5);//执行的线程Thread []threadArray = new Thread[lists.size()];//监控子线程执行完毕,再执行主线程,要不然会导致主线程关闭,子线程也会随着关闭CountDownLatch countDownLatch = new CountDownLatch(lists.size());AtomicBoolean atomicBoolean = new AtomicBoolean(true);for (int i =0;i<lists.size();i++){if (i==lists.size()-1){atomicBoolean.set(false);}List<EmployeeDO> list  = lists.get(i);threadArray[i] =  new Thread(() -> {try {//最后一个线程抛出异常if (!atomicBoolean.get()){throw new ServiceException("001","出现异常");}//批量添加,mybatisPlus中自带的batch方法this.saveBatch(list);}finally {countDownLatch.countDown();}});}for (int i = 0; i <lists.size(); i++){service.execute(threadArray[i]);}//当子线程执行完毕时,主线程再往下执行countDownLatch.await();System.out.println("添加完毕");}catch (Exception e){log.info("error",e);throw new ServiceException("002","出现异常");}finally {connection.close();}
}

数据库中存在一条数据：

//测试用例
@RunWith(SpringRunner.class)
@SpringBootTest(classes = { ThreadTest01.class, MainApplication.class})
public class ThreadTest01 {@Resourceprivate EmployeeBO employeeBO;/***   测试多线程事务.* @throws InterruptedException*/@Testpublic  void MoreThreadTest2() throws InterruptedException {int size = 10;List<EmployeeDO> employeeDOList = new ArrayList<>(size);for (int i = 0; i<size;i++){EmployeeDO employeeDO = new EmployeeDO();employeeDO.setEmployeeName("lol"+i);employeeDO.setAge(18);employeeDO.setGender(1);employeeDO.setIdNumber(i+"XX");employeeDO.setCreatTime(Calendar.getInstance().getTime());employeeDOList.add(employeeDO);}try {employeeBO.saveThread(employeeDOList);System.out.println("添加成功");}catch (Exception e){e.printStackTrace();}}
}

测试结果：

可以发现子线程组执行时，有一个线程执行失败，其他线程也会抛出异常，但是主线程中执行的删除操作，没有回滚，@Transactional注解没有生效。

使用sqlSession控制手动提交事务

 @ResourceSqlContext sqlContext;/*** 测试多线程事务.* @param employeeDOList*/
@Override
public void saveThread(List<EmployeeDO> employeeDOList) throws SQLException {// 获取数据库连接,获取会话(内部自有事务)SqlSession sqlSession = sqlContext.getSqlSession();Connection connection = sqlSession.getConnection();try {// 设置手动提交connection.setAutoCommit(false);//获取mapperEmployeeMapper employeeMapper = sqlSession.getMapper(EmployeeMapper.class);//先做删除操作employeeMapper.delete(null);//获取执行器ExecutorService service = ExecutorConfig.getThreadPool();List<Callable<Integer>> callableList  = new ArrayList<>();//拆分listList<List<EmployeeDO>> lists=averageAssign(employeeDOList, 5);AtomicBoolean atomicBoolean = new AtomicBoolean(true);for (int i =0;i<lists.size();i++){if (i==lists.size()-1){atomicBoolean.set(false);}List<EmployeeDO> list  = lists.get(i);//使用返回结果的callable去执行,Callable<Integer> callable = () -> {//让最后一个线程抛出异常if (!atomicBoolean.get()){throw new ServiceException("001","出现异常");}return employeeMapper.saveBatch(list);};callableList.add(callable);}//执行子线程List<Future<Integer>> futures = service.invokeAll(callableList);for (Future<Integer> future:futures) {//如果有一个执行不成功,则全部回滚if (future.get()<=0){connection.rollback();return;}}connection.commit();System.out.println("添加完毕");}catch (Exception e){connection.rollback();log.info("error",e);throw new ServiceException("002","出现异常");}finally {connection.close();}
}
// sql
<insert id="saveBatch" parameterType="List">INSERT INTOemployee (employee_id,age,employee_name,birth_date,gender,id_number,creat_time,update_time,status)values<foreach collection="list" item="item" index="index" separator=",">(#{item.employeeId},#{item.age},#{item.employeeName},#{item.birthDate},#{item.gender},#{item.idNumber},#{item.creatTime},#{item.updateTime},#{item.status})</foreach></insert>

数据库中一条数据：

测试结果：抛出异常，

删除操作的数据回滚了，数据库中的数据依旧存在，说明事务成功了。

成功操作示例：

 @Resource
SqlContext sqlContext;
/*** 测试多线程事务.* @param employeeDOList*/
@Override
public void saveThread(List<EmployeeDO> employeeDOList) throws SQLException {// 获取数据库连接,获取会话(内部自有事务)SqlSession sqlSession = sqlContext.getSqlSession();Connection connection = sqlSession.getConnection();try {// 设置手动提交connection.setAutoCommit(false);EmployeeMapper employeeMapper = sqlSession.getMapper(EmployeeMapper.class);//先做删除操作employeeMapper.delete(null);ExecutorService service = ExecutorConfig.getThreadPool();List<Callable<Integer>> callableList  = new ArrayList<>();List<List<EmployeeDO>> lists=averageAssign(employeeDOList, 5);for (int i =0;i<lists.size();i++){List<EmployeeDO> list  = lists.get(i);Callable<Integer> callable = () -> employeeMapper.saveBatch(list);callableList.add(callable);}//执行子线程List<Future<Integer>> futures = service.invokeAll(callableList);for (Future<Integer> future:futures) {if (future.get()<=0){connection.rollback();return;}}connection.commit();System.out.println("添加完毕");}catch (Exception e){connection.rollback();log.info("error",e);throw new ServiceException("002","出现异常");// throw new ServiceException(ExceptionCodeEnum.EMPLOYEE_SAVE_OR_UPDATE_ERROR);}
}

测试结果：