經過樂觀鎖解決庫存超賣的問題

時間 2020-03-01

標籤經過樂觀解決庫存賣的問題简体版

原文原文鏈接

前言

在經過多線程來解決高併發的問題上，線程安全每每是最早須要考慮的問題，其次纔是性能。庫存超賣問題是有不少種技術解決方案的，好比悲觀鎖，分佈式鎖，樂觀鎖，隊列串行化，Redis原子操做等。本篇經過MySQL樂觀鎖來演示基本實現。java

開發前準備

1. 環境參數

開發工具：IDEA
基礎工具：Maven+JDK8
所用技術：SpringBoot+Mybatis
數據庫：MySQL5.7
SpringBoot版本：2.2.5.RELEASE

2. 建立數據庫

基本的scheme已建好，演示就拿最簡單的數據結構最好不過了。mysql

DROP TABLE IF EXISTS `goods`;
CREATE TABLE `goods` (
  `id` int(11) NOT NULL AUTO_INCREMENT COMMENT '商品id',
  `name` varchar(30) DEFAULT NULL COMMENT '商品名稱',
  `stock` int(11) DEFAULT '0' COMMENT '商品庫存',
  `version` int(11) DEFAULT '0' COMMENT '併發版本控制',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT '商品表';

INSERT INTO `goods` VALUES (1, 'iphone', 10, 0);
INSERT INTO `goods` VALUES (2, 'huawei', 10, 0);

DROP TABLE IF EXISTS `order`;
CREATE TABLE `order` (
  `id` int(11) AUTO_INCREMENT,
  `uid` int(11) COMMENT '用戶id',
  `gid` int(11) COMMENT '商品id',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT '訂單表';

沒有環境的小夥伴能夠經過Docker實戰之MySQL主從複製，快速的進行MySQL環境的搭建。建立數據庫test,而後導入相關的sql初始化Table。web

3. 配置 pom 文件中的相關依賴

下邊是pom.xml依賴配置。spring

<dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.mybatis.spring.boot</groupId>
            <artifactId>mybatis-spring-boot-starter</artifactId>
            <version>2.1.1</version>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-devtools</artifactId>
            <scope>runtime</scope>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>

4. 配置 application.yml

因爲演示中MyBatis基於接口映射，配置簡單。application.yml中只須要配置mysql相關便可sql

spring:
  datasource:
    type: com.zaxxer.hikari.HikariDataSource
    driverClassName: com.mysql.cj.jdbc.Driver
    url: jdbc:mysql://localhost:3307/test?allowMultiQueries=true&useUnicode=true&characterEncoding=UTF-8&useSSL=false&serverTimezone=UTC
    username: root
    password: root

5. 建立相關Bean

package com.idcmind.ants.entity;

public class Goods {

    private int id;
    private String name;
    private int stock;
    private int version;
    ...
    此處省略getter、setter以及 toString方法
}

public class Order {

    private int id;
    private int uid;
    private int gid;
    ...
    此處省略getter、setter以及 toString方法
}

樂觀鎖解決庫存超賣方案

1. Dao層開發

GoodsDao.java數據庫

@Mapper
public interface GoodsDao {

    /**
     * 查詢商品庫存
     * @param id 商品id
     * @return
     */
    @Select("SELECT * FROM goods WHERE id = #{id}")
    Goods getStock(@Param("id") int id);

    /**
     * 樂觀鎖方案扣減庫存
     * @param id 商品id
     * @param version 版本號
     * @return
     */
    @Update("UPDATE goods SET stock = stock - 1, version = version + 1 WHERE id = #{id} AND stock > 0 AND version = #{version}")
    int decreaseStockForVersion(@Param("id") int id, @Param("version") int version);
}

OrderDao.javasegmentfault

這裏須要特別注意，因爲order是sql中的關鍵字，因此表名須要加上反引號。安全

@Mapper
public interface OrderDao {
    
    /**
     * 插入訂單
     * 注意: order表是關鍵字，須要`order`
     * @param order
     */
    @Insert("INSERT INTO `order` (uid, gid) VALUES (#{uid}, #{gid})")
    @Options(useGeneratedKeys = true, keyProperty = "id")
    int insertOrder(Order order);
}

2. Service層開發

GoodsService.java數據結構

@Service
public class GoodsService {

    @Autowired
    private GoodsDao goodsDao;
    @Autowired
    private OrderDao orderDao;

    /**
     * 扣減庫存
     * @param gid 商品id
     * @param uid 用戶id
     * @return SUCCESS 1 FAILURE 0
     */
    @Transactional
    public int sellGoods(int gid, int uid) {

        // 獲取庫存
        Goods goods = goodsDao.getStock(gid);
        if (goods.getStock() > 0) {
            // 樂觀鎖更新庫存
            int update = goodsDao.decreaseStockForVersion(gid, goods.getVersion());
            // 更新失敗，說明其餘線程已經修改過數據，本次扣減庫存失敗，能夠重試必定次數或者返回
            if (update == 0) {
                return 0;
            }
            // 庫存扣減成功，生成訂單
            Order order = new Order();
            order.setUid(uid);
            order.setGid(gid);
            int result = orderDao.insertOrder(order);
            return result;
        }
        // 失敗返回
        return 0;
    }
}

併發測試

這裏咱們寫個單元測試進行併發測試。mybatis

@SpringBootTest
class GoodsServiceTest {

    @Autowired
    GoodsService goodsService;

    @Test
    void seckill() throws InterruptedException {

        // 庫存初始化爲10，這裏經過CountDownLatch和線程池模擬100個併發
        int threadTotal = 100;

        ExecutorService executorService = Executors.newCachedThreadPool();

        final CountDownLatch countDownLatch = new CountDownLatch(threadTotal);
        for (int i = 0; i < threadTotal ; i++) {
            int uid = i;
            executorService.execute(() -> {
                try {
                    goodsService.sellGoods(1, uid);
                } catch (Exception e) {
                    e.printStackTrace();
                }
                countDownLatch.countDown();
            });
        }
        
        countDownLatch.await();
        executorService.shutdown();

    }
}

查看數據庫驗證是否超賣