版本号扣减库存

表结构

CREATE TABLE `price_version` (
  `id` int(11) NOT NULL AUTO_INCREMENT COMMENT '主键',
  `total` decimal(12,2) DEFAULT '0.00' COMMENT '总值',
  `version` int(11) DEFAULT '0' COMMENT '并发版本控制',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=1268 DEFAULT CHARSET=utf8;

SQL语句：

update price_version set  version=version+1 ,total=total-1 where id=#{id} AND  version =#{version} AND total >0 

代码：

    @Test
    public  void testVersion()throws Exception{
        final CountDownLatch countDownLatch=new CountDownLatch(3);
        for (int i = 0; i < 10; i++) {

            Thread thread=new Thread(new Runnable() {
                @Override
                public void run() {
//                    countDownLatch.countDown();
                    PriceVersion priceVersion = priceVersionMapper.selectById(1);
                    int count= priceVersionService.updateByVersion(priceVersion);
                    if (count == 0){
                        logger.info(Thread.currentThread().getName()+"--更新失败");
                    }else {
                        logger.info(Thread.currentThread().getName()+"--更新成功");
                    }
                }
            });

            thread.start();
        }
//        countDownLatch.await();
        Thread.sleep(2000);
        System.out.println("所有测试任务全部完成");
    }
}

结果：

[2021-06-26 20:36:51] [Thread-9] INFO  com.xulei.test.TestPriceVersion - Thread-9--更新失败
[2021-06-26 20:36:51] [Thread-8] INFO  com.xulei.test.TestPriceVersion - Thread-8--更新失败
[2021-06-26 20:36:51] [Thread-12] DEBUG c.x.l.d.P.updateLock - <==    Updates: 0
[2021-06-26 20:36:51] [Thread-12] INFO  com.xulei.test.TestPriceVersion - Thread-12--更新失败
[2021-06-26 20:36:51] [Thread-7] DEBUG c.x.l.d.P.updateLock - <==    Updates: 0
[2021-06-26 20:36:51] [Thread-7] INFO  com.xulei.test.TestPriceVersion - Thread-7--更新失败
[2021-06-26 20:36:51] [Thread-10] INFO  com.xulei.test.TestPriceVersion - Thread-10--更新成功
[2021-06-26 20:36:51] [Thread-5] DEBUG c.x.l.d.P.updateLock - <==    Updates: 0
[2021-06-26 20:36:51] [Thread-4] DEBUG c.x.l.d.P.updateLock - <==    Updates: 0
[2021-06-26 20:36:51] [Thread-4] INFO  com.xulei.test.TestPriceVersion - Thread-4--更新失败
[2021-06-26 20:36:51] [Thread-5] INFO  com.xulei.test.TestPriceVersion - Thread-5--更新失败
[2021-06-26 20:36:51] [Thread-11] DEBUG c.x.l.d.P.updateLock - <==    Updates: 0
[2021-06-26 20:36:51] [Thread-11] INFO  com.xulei.test.TestPriceVersion - Thread-11--更新失败
[2021-06-26 20:36:51] [Thread-3] DEBUG c.x.l.d.P.updateLock - <==    Updates: 0
[2021-06-26 20:36:51] [Thread-6] DEBUG c.x.l.d.P.updateLock - <==    Updates: 0
[2021-06-26 20:36:51] [Thread-6] INFO  com.xulei.test.TestPriceVersion - Thread-6--更新失败
[2021-06-26 20:36:51] [Thread-3] INFO  com.xulei.test.TestPriceVersion - Thread-3--更新失败

分析：
1：使用数据库本身，update作为锁机制存在问题。
C线程查出来是10个
A线程扣减1个，剩9个
B线程更新了库存，变回10个
C更新的时候发现还是10个，则更新成功，
虽然最后C是更新成功了。但是处理业务期间，可能不知道变动情况。所以避免这个问题，要求不管谁修改了库存，一定要加个version递增版本号。

数据读取后，更新前数据被别人篡改过，version只能做递增
场景：商品秒杀、优惠券方法，需要记录库存操作前后的业务