使用锁解决电商中的超卖

一、如何使用锁解决电商中的超卖的问题？

1、模拟5个线程并发执行。使用CyclicBarrier类

package com.example.distributedemo;

import com.example.distributedemo.service.OrderService;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;

import java.util.concurrent.CountDownLatch;
import java.util.concurrent.CyclicBarrier;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

@RunWith(SpringRunner.class)
@SpringBootTest
public class DistributeDemoApplicationTests {
    @Autowired
    private OrderService orderService;

    @Test
    public void concurrentOrder() throws InterruptedException {
        Thread.sleep(60000);
        CountDownLatch cdl = new CountDownLatch(5);
        CyclicBarrier cyclicBarrier = new CyclicBarrier(5);

        ExecutorService es = Executors.newFixedThreadPool(5);
        for (int i =0;i<5;i++){
            es.execute(()->{
                try {
                    cyclicBarrier.await();
                    Integer orderId = orderService.createOrder();
                    System.out.println("订单id："+orderId);
                } catch (Exception e) {
                    e.printStackTrace();
                }finally {
                    cdl.countDown();
                }
            });
        }
        cdl.await();
        es.shutdown();
    }

}

 

二、 基于ReentrantLock锁解决超卖问题（方法锁）

 通过手动获取事务，commit 和 rollback 检验库存和扣减库存

package com.example.distributedemo.service;

import com.example.distributedemo.dao.OrderItemMapper;
import com.example.distributedemo.dao.OrderMapper;
import com.example.distributedemo.dao.ProductMapper;
import com.example.distributedemo.model.Order;
import com.example.distributedemo.model.OrderItem;
import com.example.distributedemo.model.Product;
import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import org.springframework.transaction.PlatformTransactionManager;
import org.springframework.transaction.TransactionDefinition;
import org.springframework.transaction.TransactionStatus;
import org.springframework.transaction.annotation.Transactional;

import javax.annotation.Resource;
import java.math.BigDecimal;
import java.util.Date;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

@Service
@Slf4j
public class OrderService {

    @Resource
    private OrderMapper orderMapper;
    @Resource
    private OrderItemMapper orderItemMapper;
    @Resource
    private ProductMapper productMapper;
    //购买商品id
    private int purchaseProductId = 100100;
    //购买商品数量
    private int purchaseProductNum = 1;
    @Autowired
    private PlatformTransactionManager platformTransactionManager;
    @Autowired
    private TransactionDefinition transactionDefinition;

    private Lock lock = new ReentrantLock();


//    @Transactional(rollbackFor = Exception.class)
    public Integer createOrder() throws Exception{
        Product product = null;

        lock.lock();
        try {
            TransactionStatus transaction1 = platformTransactionManager.getTransaction(transactionDefinition);
            product = productMapper.selectByPrimaryKey(purchaseProductId);
            if (product==null){
                platformTransactionManager.rollback(transaction1);
                throw new Exception("购买商品："+purchaseProductId+"不存在");
            }

            //商品当前库存
            Integer currentCount = product.getCount();
            System.out.println(Thread.currentThread().getName()+"库存数："+currentCount);
            //校验库存
            if (purchaseProductNum > currentCount){
                platformTransactionManager.rollback(transaction1);
                throw
                        new Exception("商品"+purchaseProductId+"仅剩"+currentCount+"件，无法购买");
            }

            productMapper.updateProductCount(purchaseProductNum,"xxx",new Date(),product.getId());
            platformTransactionManager.commit(transaction1);
        }finally {
            lock.unlock();
        }

        TransactionStatus transaction = platformTransactionManager.getTransaction(transactionDefinition);
        Order order = new Order();
        order.setOrderAmount(product.getPrice().multiply(new BigDecimal(purchaseProductNum)));
        order.setOrderStatus(1);//待处理
        order.setReceiverName("xxx");
        order.setReceiverMobile("13311112222");
        order.setCreateTime(new Date());
        order.setCreateUser("xxx");
        order.setUpdateTime(new Date());
        order.setUpdateUser("xxx");
        orderMapper.insertSelective(order);

        OrderItem orderItem = new OrderItem();
        orderItem.setOrderId(order.getId());
        orderItem.setProductId(product.getId());
        orderItem.setPurchasePrice(product.getPrice());
        orderItem.setPurchaseNum(purchaseProductNum);
        orderItem.setCreateUser("xxx");
        orderItem.setCreateTime(new Date());
        orderItem.setUpdateTime(new Date());
        orderItem.setUpdateUser("xxx");
        orderItemMapper.insertSelective(orderItem);
        platformTransactionManager.commit(transaction);
        return order.getId();
    }

}