分布式锁：jvm本地加锁解决商品超卖的方案

news2024/11/19 0:20:18

一分布式锁

1.1 分布式锁的作用

在多线程高并发场景下，为了保证资源的线程安全问题，jdk为我们提供了synchronized关键字和ReentrantLock可重入锁，但是它们只能保证一个工程内的线程安全。在分布式集群、微服务、云原生横行的当下，如何保证不同进程、不同服务、不同机器的线程安全问题。jdk并没有给我们提供既有的解决方案。需要自己通过编写方案来解决，目前主流的实现有以下方式：

基于mysql关系型实现
基于redis非关系型数据实现
基于zookeeper/etcd实现

二模拟单体超卖

2.1 工程结构

2.2 编写工程代码

1.pom文件

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

        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.46</version>
        </dependency>

        <dependency>
            <groupId>com.baomidou</groupId>
            <artifactId>mybatis-plus-boot-starter</artifactId>
            <version>3.4.1</version>
        </dependency>

        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>1.18.16</version>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-redis</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-devtools</artifactId>
            <version>2.3.12.RELEASE</version>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
            <exclusions>
                <exclusion>
                    <groupId>org.junit.vintage</groupId>
                    <artifactId>junit-vintage-engine</artifactId>
                </exclusion>
            </exclusions>
        </dependency>

2.配置文件

server.port=9999
spring.datasource.driver-class-name=com.mysql.jdbc.Driver
spring.datasource.url=jdbc:mysql://localhost:3306/fenbu_lock?characterEncoding=utf-8&useSSL=true
spring.datasource.username=root
spring.datasource.password=cloudiip
redis.host=172.16.116.100

3.controller

@RestController
public class StockController {

    @Autowired
    private StockService stockService;

    @GetMapping("stock/deduct")
    public String deduct(){
       // this.stockService.deduct();
        this.stockService.deductByMsqlDb();
        return "hello stock deduct！！";
    }

}

4.service

@Service
public class StockService {
    @Autowired
    private StockMapper stockMapper;
    private Stock stock = new Stock();

    private ReentrantLock lock = new ReentrantLock();

    public void deduct(){
//        lock.lock();
//        try {
//            stock.setStock(stock.getStock() - 1);
//            System.out.println("库存余量：" + stock.getStock());
//        } finally {
//            lock.unlock();
//        }
    }
    public void deductByMsqlDb(){
        // 先查询库存是否充足
        Stock stock = this.stockMapper.selectById(1L);

        // 再减库存
        if (stock != null && stock.getCount() > 0){
            stock.setCount(stock.getCount() - 1);
            this.stockMapper.updateById(stock);
        }
    }

}

5.mapper


@Mapper
public interface StockMapper extends BaseMapper<Stock> {
}

6.启动类

@SpringBootApplication
@MapperScan("com.atguigu.distributed.lock.mapper")
public class DistributedLockApplication {

    public static void main(String[] args)
    {
        SpringApplication.run(DistributedLockApplication.class, args);
        System.out.println("========================启动成功==========");
    }

}

7.pojo类

@Data
@TableName("db_stock")
public class Stock {
    @TableId
    private Long id;

    private String productCode;

    private String stockCode;

    private Integer count;
   // private Integer stock = 5000;
}

8.附件数据表

1.新建一个数据库，附件数据表，如图

2.脚本文件

CREATE TABLE `db_stock` (
  `id` bigint(20) NOT NULL AUTO_INCREMENT,
  `product_code` varchar(255) DEFAULT NULL COMMENT '商品编号',
  `stock_code` varchar(255) DEFAULT NULL COMMENT '仓库编号',
  `count` int(11) DEFAULT NULL COMMENT '库存量',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8;