Redis分布式锁--Redisson

一、Redisson

• 一个用来进行分布式锁的工具类

 <dependency>
     <groupId>org.redisson</groupId>
     <artifactId>redisson</artifactId>
     <version>3.16.8</version>
 </dependency>

1. 基本Demo

package com.erick.redis;

import org.redisson.Redisson;
import org.redisson.api.RLock;
import org.redisson.api.RedissonClient;
import org.redisson.config.Config;

import java.util.concurrent.TimeUnit;

public class Test03 {
    public static void main(String[] args) {
        new Thread(() -> lockWithBusiness()).start();
        new Thread(() -> lockWithBusiness()).start();
    }

    private static void lockWithBusiness() {
        RedissonClient redissonClient = redissonClient();
        /*获取对应的key的锁*/
        String lockKey = "COMMERCE-BUSINESS";
        RLock lock = redissonClient.getLock(lockKey);

        try {
            // 内部包含重试时间
            /*参数一： 最长等待时间
             * 参数二：锁超时释放时间
             * 参数三：时间单位*/
            boolean hasLok = lock.tryLock();

            if (hasLok) {
                business();
            } else {
                System.out.println("暂时没有获取到锁");
            }
        } finally {
            /*第二个锁释放的时候，会报 删除异常
             * IllegalMonitorStateException*/
            lock.unlock();
        }
    }

    /*等待超时的锁*/
    private static void lockWithBusinessWithTime() {
        RedissonClient redissonClient = redissonClient();
        /*获取对应的key的锁*/
        String lockKey = "COMMERCE-BUSINESS";
        RLock lock = redissonClient.getLock(lockKey);

        try {
            // 内部包含重试时间
            /*参数一： 最长等待时间
             * 参数二：锁超时释放时间
             * 参数三：时间单位*/
            boolean hasLok = lock.tryLock(6, 20, TimeUnit.SECONDS);

            if (hasLok) {
                business();
            } else {
                System.out.println("暂时没有获取到锁");
            }
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            //  最长等待时间获取不到，删除的时候依然会报错
            lock.unlock();
        }
    }

    private static void business() {
        System.out.println("执行业务");
        try {
            TimeUnit.SECONDS.sleep(5);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    /*Redis的配置类*/
    private static RedissonClient redissonClient() {
        Config config = new Config();
        config.useSingleServer().setAddress("redis://60.205.229.31:6380");
        return Redisson.create(config);
    }
}

2. 可重入性

2.1 不可重入锁

2.2 可重入锁

• 存储的键值对用Hash结构来保存
• 为了保证多条命令的原子性，必须采取lua脚本来做

2.3 lua脚本

3. 重试机制

• 通过等待时间结合，发布以及订阅模式来实现

4. 主从一致性

4.1 问题

4.2 联锁

• 解决方案：设立多个redis作为主节点
• 只有每个都获取成功的时候，才会去执行
  

package com.erick.redis;

import org.redisson.Redisson;
import org.redisson.api.RLock;
import org.redisson.api.RedissonClient;
import org.redisson.config.Config;

import java.util.concurrent.TimeUnit;

public class Test04 {
    public static void main(String[] args) {
        businessWithLock();
    }

    private static void businessWithLock() {
        String lockKey = "BUSINESS";
        RedissonClient firstClient = redissonClient01();
        RedissonClient secondClient = redissonClient02();
        RedissonClient thirdClient = redissonClient03();

        RLock firstLock = firstClient.getLock(lockKey);
        RLock secondLock = secondClient.getLock(lockKey);
        RLock thirdLock = thirdClient.getLock(lockKey);

        /*获取到多把锁*/
        RLock multiLock = firstClient.getMultiLock(firstLock, secondLock, thirdLock);

        boolean hasLock = multiLock.tryLock();
        try{
            if (hasLock) {
                business();
            } else {
                System.out.println("未获取到锁，业务没有执行");
            }
        }finally {
            multiLock.unlock();
        }
    }

    private static void business() {
        System.out.println("执行业务");
        try {
            TimeUnit.SECONDS.sleep(5);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    /*Redis的配置类*/
    private static RedissonClient redissonClient01() {
        Config config = new Config();
        config.useSingleServer().setAddress("redis://60.205.229.31:6379");
        return Redisson.create(config);
    }

    private static RedissonClient redissonClient02() {
        Config config = new Config();
        config.useSingleServer().setAddress("redis://60.205.229.31:6380");
        return Redisson.create(config);
    }

    private static RedissonClient redissonClient03() {
        Config config = new Config();
        config.useSingleServer().setAddress("redis://60.205.229.31:6381");
        return Redisson.create(config);
    }
}