【技术分享】多线程事务怎么回滚？

【技术分享】多线程事务怎么回滚？

一 场景介绍

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。

二 代码演示

1. 线程池配置类

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(){}
}

2. sqlSession工具类

@Component
public class SqlContext {
    @Resource
    private SqlSessionTemplate sqlSessionTemplate;

    public SqlSession getSqlSession(){
        SqlSessionFactory sqlSessionFactory = sqlSessionTemplate.getSqlSessionFactory();
        return sqlSessionFactory.openSession();
    }
}

3. 拆分list工具类

/**
 * 平均拆分list方法.
 * @param source
 * @param n
 * @param 
 * @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;
}

4. 多线程使用手动提交事务实现事务回滚
   操作失败

 @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);
        //获取mapper
        EmployeeMapper 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list
        List<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 INTO
 employee (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>

操作成功

 @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);
    }
}