5

我正在尝试了解 Spring 事务的隔离级别。这是我正在使用的示例：

@Component
public class BookShop {

    private Object lockObj = new Object();

    @Autowired
    private BookDao bookDao;

    @Transactional
    public void increaseStock(int isbn, int increment){
        String threadName = Thread.currentThread().getName();
        synchronized (lockObj) {
            Book book = bookDao.findByIsbn(isbn);
            System.out.println(threadName+" about to increment the stock");
            bookDao.updateStock(book, 5);
        }
        System.out.println(threadName+" has increased the stock ");
        sleep(threadName);
        System.out.println(threadName+" rolled back stock");
        throw new RuntimeException("Stock increased by mistake");
    }

    @Transactional
    public int checkStock(int isbn){
        int stock = 0;
        String threadName = Thread.currentThread().getName();
        synchronized (lockObj) {
            System.out.println(threadName+" checking for the stock");
            stock = bookDao.getStock(isbn);
        }
        System.out.println(threadName+": Stock is: "+stock);
        sleep(threadName);
        return stock;
    }

    private void sleep(String threadName){
        System.out.println(threadName+" sleeping");
        try{
            Thread.sleep(1000);
        }catch (InterruptedException e) {
        }
        System.out.println(threadName+" wakeup!");
    }

}

这就是我调用上述内容的方式：

public void testIsolationLevels(final BookShop bookShop, final int isbn){
        Thread t1 = new Thread(){
            public void run() {
                bookShop.increaseStock(isbn, 5);
            };
        };
        t1.setPriority(Thread.MAX_PRIORITY);
        t1.start();

        Thread t2 = new Thread(){
            public void run() {
                bookShop.checkStock(isbn);
            };
        };
        t2.setPriority(Thread.MIN_PRIORITY);
        t2.start();
    }

这是交易配置：

<tx:advice id="bookTxn" transaction-manager="transactionManager">
        <tx:attributes> 
            <tx:method name="updateStock" isolation="READ_UNCOMMITTED"/>
            <tx:method name="getStock" isolation="READ_UNCOMMITTED"/>
        </tx:attributes>
    </tx:advice>

    <aop:config>
        <aop:pointcut expression="execution(* com.pramati.springIdol.dao.BookDao+.*(..))" id="bookPC"/>
        <aop:advisor advice-ref="bookTxn"  pointcut-ref="bookPC"/>
    </aop:config>

但是当我运行示例时，这是我得到的 o/p：

Thread-2 about to increment the stock// Initially it is 99
Thread-2 has increased the stock // Now it is 104(99+5)
Thread-2 sleeping
Thread-3 checking for the stock
Thread-3: Stock is: 99//Why is it not 104 even if isolation level is read_uncommitted??
Thread-3 sleeping
Thread-2 wakeup!
Thread-2 rolled back stock
Thread-3 wakeup!
Exception in thread "Thread-2" java.lang.RuntimeException: Stock increased by mistake

我认为 Thread-3 将能够读取更新的值。但事实并非如此。有人可以让我知道我哪里出错了吗？

提前致谢！

4

1 回答 1

3

这里的问题是我从另一个事务方法（BookShop 的方法）调用 DAO 的事务方法。

由于我没有为 BookShop 的方法指定隔离级别，所以默认的隔离级别是 Isolation.READ_COMMITTED。

另请注意，我没有为 Dao 的方法指定传播行为，默认行为是 Propagation.REQUIRED。因此 dao 方法使用与 BookShop 相同的事务。因此 Isolation.READ_COMMITTED 的隔离被应用于事务。

解决方案是：将 BookShop 方法的隔离级别指定为 READ_UNCOMMITTED

于 2012-06-21T15:02:53.573 回答