Redis实现分布式锁

一、通过Redis分布式锁双重防死锁

1、Redis分布式锁命令：

setnx: 只有不存在的时候才set

getset: 先get再set

expire: 设置key的有效期

del: 删除

2、Redis分布式锁优化版流程图

代码实现：

@Scheduled(cron="0 */1 * * * ?")
public void closeOrderTaskV3(){
    log.info("关闭订单定时任务启动");
    long lockTimeout = Long.parseLong(PropertiesUtil.getProperty("lock.timeout","5000"));
    Long setnxResult = RedisShardedPoolUtil.setnx(Const.REDIS_LOCK.CLOSE_ORDER_TASK_LOCK,String.valueOf(System.currentTimeMillis()+lockTimeout));
    if(setnxResult != null && setnxResult.intValue() == 1){
        closeOrder(Const.REDIS_LOCK.CLOSE_ORDER_TASK_LOCK);
    }else{
        //未获取到锁，继续判断，判断时间戳，看是否可以重置并获取到锁
        String lockValueStr = RedisShardedPoolUtil.get(Const.REDIS_LOCK.CLOSE_ORDER_TASK_LOCK);
        if(lockValueStr != null && System.currentTimeMillis() > Long.parseLong(lockValueStr)){
            String getSetResult = RedisShardedPoolUtil.getSet(Const.REDIS_LOCK.CLOSE_ORDER_TASK_LOCK,String.valueOf(System.currentTimeMillis()+lockTimeout));
            //再次用当前时间戳getset。
            //返回给定的key的旧值，->旧值判断，是否可以获取锁
            //当key没有旧值时，即key不存在时，返回nil ->获取锁
            //这里我们set了一个新的value值，获取旧的值。
            if(getSetResult == null || (getSetResult != null && StringUtils.equals(lockValueStr,getSetResult))){
                //真正获取到锁
                closeOrder(Const.REDIS_LOCK.CLOSE_ORDER_TASK_LOCK);
            }else{
                log.info("没有获取到分布式锁:{}",Const.REDIS_LOCK.CLOSE_ORDER_TASK_LOCK);
            }
        }else{
            log.info("没有获取到分布式锁:{}",Const.REDIS_LOCK.CLOSE_ORDER_TASK_LOCK);
        }
    }
    log.info("关闭订单定时任务结束");
}



private void closeOrder(String lockName){
    RedisShardedPoolUtil.expire(lockName,5);//有效期50秒，防止死锁
    log.info("获取{},ThreadName:{}",Const.REDIS_LOCK.CLOSE_ORDER_TASK_LOCK,Thread.currentThread().getName());
    int hour = Integer.parseInt(PropertiesUtil.getProperty("close.order.task.time.hour","2"));
    iOrderService.closeOrder(hour);
    RedisShardedPoolUtil.del(Const.REDIS_LOCK.CLOSE_ORDER_TASK_LOCK);
    log.info("释放{},ThreadName:{}",Const.REDIS_LOCK.CLOSE_ORDER_TASK_LOCK,Thread.currentThread().getName());
    log.info("===============================");
}

二、Redisson框架实现分布式锁

1、Redisson介绍

Redisson是架设在Redis基础上的一个Java驻内存数据网络(In-Memort-Data-Grid)
Redisson在基于NIO的Netty框架上，充分的利用了Redis键值数据库提供的一系列优势
在Java实用工具包中常用接口的基础上，为使用者提供了一系列具有分布式特性的常用工具类
使得原本为协调单机多线程并发程序的工具包获得了协调分布式多机多线程并发系统的能力，大大降低了设计和研发大规模分布式系统的难度。
同时结合各富特色的分布式服务，更进一步简化了分布式环境中程序相互之间的协作
Redisson官网：https://redisson.org Redisson Github: https://github.com/redisson/ Redisson Wiki：https://github.com/redisson/redisson/wiki

2、引入maven依赖

<dependency>
  <groupId>org.springframework.session</groupId>
  <artifactId>spring-session-data-redis</artifactId>
  <version>1.2.0.RELEASE</version>
</dependency>
<dependency>
  <groupId>org.redisson</groupId>
  <artifactId>redisson</artifactId>
  <version>2.9.0</version>
</dependency>
<dependency>
  <groupId>com.fasterxml.jackson.dataformat</groupId>
  <artifactId>jackson-dataformat-avro</artifactId>
  <version>2.9.0</version>
</dependency>

3、Redisson工具类封装：

package com.mmall.common;

import com.mmall.util.PropertiesUtil;
import lombok.extern.slf4j.Slf4j;
import org.springframework.stereotype.Component;
import org.redisson.Redisson;
import org.redisson.config.Config;
import javax.annotation.PostConstruct;

/**
 * @Author: chenyawei
 * @Date: 2020-04-20  11:39
 * @Description:
 */
@Component
@Slf4j
public class RedissonManager {

    private Config config = new Config();
    private Redisson redisson = null;

    public Redisson getRedisson() {
        return redisson;
    }
    private static String redis1Ip = PropertiesUtil.getProperty("redis1.ip");
    private static Integer redis1Port = Integer.parseInt(PropertiesUtil.getProperty("redis1.port"));
    private static String redis2Ip = PropertiesUtil.getProperty("redis2.ip");
    private static Integer redis2Port = Integer.parseInt(PropertiesUtil.getProperty("redis2.port"));

    @PostConstruct
    private void init(){
        try {
            config.useSingleServer().setAddress(new StringBuilder().append(redis1Ip).append(":").append(redis1Port).toString());

            redisson = (Redisson) Redisson.create(config);

            log.info("初始化Redisson结束");
        } catch (Exception e) {
            log.error("redisson init error",e);
        }
    }

}

3、业务代码中的使用

    //    @Scheduled(cron="0 */1 * * * ?")
    public void closeOrderTaskV4(){
        RLock lock = redissonManager.getRedisson().getLock(Const.REDIS_LOCK.CLOSE_ORDER_TASK_LOCK);
        boolean getLock = false;
        try {
            if(getLock = lock.tryLock(0,50, TimeUnit.SECONDS)){
                log.info("Redisson获取到分布式锁:{},ThreadName:{}",Const.REDIS_LOCK.CLOSE_ORDER_TASK_LOCK,Thread.currentThread().getName());
                int hour = Integer.parseInt(PropertiesUtil.getProperty("close.order.task.time.hour","2"));
//                iOrderService.closeOrder(hour);
            }else{
                log.info("Redisson没有获取到分布式锁:{},ThreadName:{}",Const.REDIS_LOCK.CLOSE_ORDER_TASK_LOCK,Thread.currentThread().getName());
            }
        } catch (InterruptedException e) {
            log.error("Redisson分布式锁获取异常",e);
        } finally {
            if(!getLock){
                return;
            }
            lock.unlock();
            log.info("Redisson分布式锁释放锁");
        }
    }


    RedisShardedPoolUtil.expire(lockName,5);//有效期50秒，防止死锁
        log.info("获取{},ThreadName:{}",Const.REDIS_LOCK.CLOSE_ORDER_TASK_LOCK,Thread.currentThread().getName());
        int hour = Integer.parseInt(PropertiesUtil.getProperty("close.order.task.time.hour","2"));
        iOrderService.closeOrder(hour);
        RedisShardedPoolUtil.del(Const.REDIS_LOCK.CLOSE_ORDER_TASK_LOCK);
        log.info("释放{},ThreadName:{}",Const.REDIS_LOCK.CLOSE_ORDER_TASK_LOCK,Thread.currentThread().getName());
        log.info("===============================");
    }

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一、通过Redis分布式锁双重防死锁

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