4、基于mysql实现分布式锁

news2024/12/23 11:37:04

4.1. 基本思路

synchronized关键字和ReetrantLock锁都是独占排他锁，即多个线程争抢一个资源时，同一时刻只有一个线程可以抢占该资源，其他线程只能阻塞等待，直到占有资源的线程释放该资源

利用唯一键索引不能重复插入的特点实现
在这里插入图片描述

4.2. 代码实现

1、创建锁表，和对应的实体类

CREATE TABLE `tb_lock` (
  `id` bigint(20) NOT NULL AUTO_INCREMENT,
  `lock_name` varchar(50) NOT NULL COMMENT '锁名',
  `class_name` varchar(100) DEFAULT NULL COMMENT '类名',
  `method_name` varchar(50) DEFAULT NULL COMMENT '方法名',
  `server_name` varchar(50) DEFAULT NULL COMMENT '服务器ip',
  `thread_name` varchar(50) DEFAULT NULL COMMENT '线程名',
  `create_time` timestamp NULL DEFAULT NULL ON UPDATE CURRENT_TIMESTAMP COMMENT '获取锁时间',
  `desc` varchar(100) DEFAULT NULL COMMENT '描述',
  PRIMARY KEY (`id`),
  UNIQUE KEY `idx_unique` (`lock_name`)
) ENGINE=InnoDB AUTO_INCREMENT=1332899824461455363 DEFAULT CHARSET=utf8;

@Data
@AllArgsConstructor
@NoArgsConstructor
@TableName("tb_lock")
public class Lock {

    private Long id;
    private String lockName;
    private String className;
    private String methodName;
    private String serverName;
    private String threadName;
    private Date createTime;
    private String desc;
}

LockMapper接口：

public interface LockMapper extends BaseMapper<Lock> {
}

改造StockService：

@Service
public class StockService {

    @Autowired
    private StockMapper stockMapper;

    @Autowired
    private LockMapper lockMapper;

    /**
     * 数据库分布式锁
     */
    public void checkAndLock() {

        // 加锁
        Lock lock = new Lock(null, "lock", this.getClass().getName(), new Date(), null);
        try {
            this.lockMapper.insert(lock);
             // 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);
	        }
        } catch (Exception ex) {
            // 获取锁失败，则重试
            try {
                Thread.sleep(50);
                this.checkAndLock();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        } finally {
	         // 释放锁
	        this.lockMapper.deleteById(lock.getId());
        }  
    }
}