经验分享：用一张表解决并发冲突！数据库事务锁的核心实现逻辑

背景

对于一些内部使用的管理系统来说，可能没有引入Redis，又想基于现有的基础设施处理并发问题，而数据库是每个应用都避不开的基础设施之一，因此分享个我曾经维护过的一个系统中，使用数据库表来实现事务锁的方式。

之前在文章Java业务功能并发问题处理中实现了使用MySQL行锁、Redis分布式锁来处理业务并发问题，这次来填坑了，如果想了解其他并发问题处理方式和区别，可以看看文章Java业务功能并发问题处理哈。

业务流程说明

业务加锁流程图

方案分析

适用场景

应用服务有多个实例，但是数据库是单实例；
没有用上Redis的应用服务，想通过现有的基础设施解决并发数据问题

待改进措施

设置超时机制：当出现锁无法及时释放时需要手动删除表数据，可以设置逻辑删除字段或者定时器删除过期数据；
重试获取锁机制：设置一定的循环次数，当获取不到锁时休眠200毫秒再次获取，直到循环次数用尽后再返回失败；
锁重入支持：通过增加加锁次数字段让当同一个线程可以重复获取锁

程序实现过程

框架及工具说明

技术框架：SpringBoot、MyBatis、Maven
数据库：MySQL
测试工具：Apifox
表设计及代码说明：
1. 唯一索引：需要有一个用于判断唯一的字段，在数据库表中通过指定唯一索引来实现；
2. 加锁的线程号：避免A线程加的锁，被B线程删除；
3. 锁的可见性要单独事务：添加事务锁的逻辑应在我们执行业务逻辑的事务之前，且不能跟业务逻辑的事务在一块，否则在事务提交前其他线程根本看不到这个锁，也就达不到我们锁的目的了；
4. 为了我们的锁更方便使用，也可以将加锁逻辑抽到注解中实现，注解的实现流程：
  - 在pom文件中引入spring-boot-starter-aop
  - 编写自定义注解ConcurrencyLock
  - 实现切面类（Aspect）逻辑

代码展示

为了能让大家更关注加解锁逻辑，本文只保留主要代码，参考链接处会放置码云（gitee）的源码地址(或者点击此处跳转)；
另外，本文就不展示注解方式的使用了，以免占用篇幅。

代码结构图

实体类

/**
 * 并发锁实体类
 */
public class ConcurrencyLockBean {
    /**
     * 数据库主键
     */
    private Long id;
    /**
     * 操作节点
     */
    private String businessNode;
    /**
     * 订单唯一编号
     */
    private String businessUniqueNo;
    /**
     * 线程ID
     */
    private Long threadId;
    /**
     * 创建日期
     */
    private Date creationDate;
}

/**
 * 订单实体类
 */
@Setter
@Getter
@ToString
public class OrderInfoBean {
    /**
     * 自增长主键
     */
    private int id;
    /**
     * 订单号
     */
    private String orderNo;
    /**
     * 物料数量
     */
    private Integer itemQty;
}

ConcurrencyLockServiceImpl.java

@Slf4j
@Service
public class ConcurrencyLockServiceImpl implements ConcurrencyLockService {
    ConcurrencyLockMapper mapper;
    /**
     * service类注入
     */
    @Autowired
    ConcurrencyLockServiceImpl(ConcurrencyLockMapper mapper) {
        this.mapper = mapper;
    }

    @Override
    public Boolean tryLock(String businessNode, String businessUniqueNo) {
        long threadId = Thread.currentThread().getId();
        ConcurrencyLockBean concurrencyLock = mapper.selectConcurrencyLock(businessNode, businessUniqueNo);
        if (concurrencyLock != null) {
            log.info("{}数据正在操作中，请稍后", threadId);
            return false;
        }

        ConcurrencyLockBean lock = new ConcurrencyLockBean();
        lock.setBusinessNode(businessNode);
        lock.setBusinessUniqueNo(businessUniqueNo);
        lock.setThreadId(threadId);
        try {
            int insertCount = mapper.insertConcurrencyLock(lock);
            if (insertCount == 0) {
                log.info("{}获取锁失败，请稍后重试", threadId);
                return false;
            }
        } catch (Exception e) {
            log.info("{}获取锁异常，请稍后重试", threadId);
            return false;
        }
        log.info("{}完成锁表插入", threadId);
        return true;
    }

    @Override
    public void unLock(String businessNode, String businessUniqueNo) {
        ConcurrencyLockBean lock = new ConcurrencyLockBean();
        long threadId = Thread.currentThread().getId();
        lock.setThreadId(threadId);
        lock.setBusinessNode(businessNode);
        lock.setBusinessUniqueNo(businessUniqueNo);
        mapper.deleteConcurrencyLock(lock);
        log.info("{}执行解锁完毕", threadId);
    }
}

ConcurrencyLockMapper.java

import org.apache.ibatis.annotations.Param;

public interface ConcurrencyLockMapper {
    /**
     * 根据业务节点和唯一业务号查询锁
     */
    ConcurrencyLockBean selectConcurrencyLock(@Param("businessNode") String businessNode, @Param("businessUniqueNo") String businessUniqueNo);

    /**
     * 插入锁
     */
    int insertConcurrencyLock(ConcurrencyLockBean lock);

    /**
     * 删除锁
     */
    int deleteConcurrencyLock(ConcurrencyLockBean lock);
}

ConcurrencyLockMapper.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.runningrookie.mapper.ConcurrencyLockMapper">
    <select id="selectConcurrencyLock" resultType="com.runningrookie.domain.ConcurrencyLockBean">
        SELECT
            THREAD_ID,
            BUSINESS_NODE,
            BUSINESS_UNIQUE_NO,
            CREATION_DATE
        FROM concurrency_lock
        WHERE BUSINESS_UNIQUE_NO = #{businessUniqueNo}
        AND BUSINESS_NODE = #{businessNode}
    </select>
    <insert id="insertConcurrencyLock" useGeneratedKeys="true" keyProperty="id">
        INSERT INTO concurrency_lock (
            THREAD_ID,
            BUSINESS_NODE,
            BUSINESS_UNIQUE_NO,
            CREATION_DATE)
        VALUES
            (#{threadId}, #{businessNode}, #{businessUniqueNo}, NOW());
    </insert>
    <delete id="deleteConcurrencyLock">
        DELETE FROM concurrency_lock
        WHERE THREAD_ID = #{threadId}
        and BUSINESS_NODE = #{businessNode}
        and BUSINESS_UNIQUE_NO = #{businessUniqueNo}
    </delete>
</mapper>

ConcurrencyLock.java注解

@Target({ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface ConcurrencyLock {
    String businessNode();
    String businessUniqueNoKey();
}

ConcurrencyLockAspect.java注解类

@Aspect
@Component
@Slf4j
public class ConcurrencyLockAspect {
    ConcurrencyLockService concurrencyLockService;
    @Autowired
    ConcurrencyLockAspect(ConcurrencyLockService concurrencyLockService) {
        this.concurrencyLockService = concurrencyLockService;
    }
    // 环绕切面
    @Around("@annotation(concurrencyLock)")
    public Object around(ProceedingJoinPoint joinPoint, ConcurrencyLock concurrencyLock) throws Throwable {
        long threadId = Thread.currentThread().getId();
        Object[] args = joinPoint.getArgs();
        if (args.length == 0) {
            return joinPoint.proceed();
        }
        // 通过反射获取值
        String invokeMethodName = "get" + concurrencyLock.businessUniqueNoKey().substring(0, 1).toUpperCase() + concurrencyLock.businessUniqueNoKey().substring(1);
        // 获取Order类的Class对象
        Class<?> clazz = args[0].getClass();
        // 获取getOrderNo方法的Method对象
        Method method = clazz.getMethod(invokeMethodName);

        // 调用getOrderNo方法并获取返回值
        String businessUniqueNo = method.invoke(args[0]).toString();
        Boolean isSuccessLock = concurrencyLockService.tryLock(concurrencyLock.businessNode(), businessUniqueNo);
        if (!isSuccessLock) {
            log.info("{}加锁失败，请稍后重试", threadId);
            // 生成与切点方法相同的返回对象
            return AjaxResult.error("加锁失败，请稍后重试");
        }
        try {
            log.info("{}开始执行业务逻辑", threadId);
            joinPoint.proceed();
        } finally {
            concurrencyLockService.unLock(concurrencyLock.businessNode(), businessUniqueNo);
        }
        return joinPoint.proceed();
    }
}

OrderInfoController.java

@RestController
@RequestMapping("/orderInfo")
public class OrderInfoController {
    OrderInfoService orderInfoService;
    @Autowired
    private OrderInfoController(OrderInfoService orderInfoService) {
        this.orderInfoService = orderInfoService;
    }
    @PostMapping
    public AjaxResult saveOrderInfo(@RequestBody OrderInfoBean bean) {
        return orderInfoService.saveOrderInfo(bean);
    }
}

OrderServiceImpl.java

/**
 * 订单逻辑代码
 */
@Slf4j
@Service
public class OrderInfoServiceImpl implements OrderInfoService {
    ConcurrencyLockService concurrencyLockService;
    /**
     * service类注入
     */
    @Autowired
    OrderInfoServiceImpl(ConcurrencyLockService concurrencyLockService) {
        this.concurrencyLockService = concurrencyLockService;
    }
    @Override
    public AjaxResult saveOrderInfo(OrderInfoBean bean) {
        long threadId = Thread.currentThread().getId();
        final String businessNode = "插入";
        Boolean isSuccessLock = concurrencyLockService.tryLock(businessNode, bean.getOrderNo());
        if (!isSuccessLock) {
            return AjaxResult.error("加锁失败，请稍后重试");
        }
        try {
            log.info("{}开始执行业务逻辑", threadId);
            // TODO:模拟业务逻辑耗时
            Thread.sleep(1500);
        } catch (InterruptedException e) {
            throw new RuntimeException(e);
        } finally {
            concurrencyLockService.unLock(businessNode, bean.getOrderNo());
        }
        return AjaxResult.success();
    }
    
    @Override
    @ConcurrencyLock(businessNode = "插入", businessUniqueNoKey = "orderNo")
    @Transactional
    public AjaxResult saveOrderInfoByAnnotation(OrderInfoBean bean) {
        // TODO:模拟业务逻辑耗时
        Thread.sleep(1500);
        return AjaxResult.success();
    }
}

pom.xml相关依赖

在dependencies中添加下列依赖

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-aop</artifactId>
</dependency>
<dependency>
    <groupId>org.mybatis.spring.boot</groupId>
    <artifactId>mybatis-spring-boot-starter</artifactId>
    <version>2.1.4</version>
</dependency>
<!-- Mysql驱动包 -->
<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
</dependency>

事务处理表的表结构

CREATE TABLE `concurrency_lock` (
  `ID` int NOT NULL AUTO_INCREMENT COMMENT '主键',
  `THREAD_ID` int DEFAULT NULL COMMENT '线程号',
  `BUSINESS_NODE` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci DEFAULT NULL COMMENT '操作节点',
  `BUSINESS_UNIQUE_NO` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci DEFAULT NULL COMMENT '单据号',
  `CREATION_DATE` datetime DEFAULT NULL COMMENT '创建时间',
  PRIMARY KEY (`ID`),
  UNIQUE KEY `uni_business_no` (`BUSINESS_UNIQUE_NO`,`BUSINESS_NODE`) USING BTREE
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_general_ci;

测试输出结果

使用Apifox并发发送5次请求，可以看到实际成功获取到锁并执行的只有一个线程

17:08:00.449 [http-nio-8080-exec-1] c.r.service.impl.ConcurrencyLockServiceImpl - 40完成锁表插入
17:08:00.462 [http-nio-8080-exec-1] c.runningrookie.service.impl.OrderInfoServiceImpl - 40开始执行业务逻辑
17:08:00.573 [http-nio-8080-exec-5] c.r.service.impl.ConcurrencyLockServiceImpl - 44获取锁异常，请稍后重试
17:08:00.573 [http-nio-8080-exec-4] c.r.service.impl.ConcurrencyLockServiceImpl - 43获取锁异常，请稍后重试
17:08:00.573 [http-nio-8080-exec-3] c.r.service.impl.ConcurrencyLockServiceImpl - 42获取锁异常，请稍后重试
17:08:00.573 [http-nio-8080-exec-2] c.r.service.impl.ConcurrencyLockServiceImpl - 41获取锁异常，请稍后重试
17:08:00.574 [http-nio-8080-exec-1] c.r.service.impl.ConcurrencyLockServiceImpl - 40执行解锁完毕