Simple implementation of distributed lock single instance redis

Basic functions include redis distributed lock, the same moment only one person occupied lock, when the lock is occupied by other people, who can wait for others to obtain the release of the lock, the lock itself must be in addition timeout automatically released.

Directly on the java code, as follows:

package com.test;

import org.apache.commons.pool2.impl.GenericObjectPoolConfig;
import redis.clients.jedis.Jedis;
import redis.clients.jedis.JedisPool;

import java.util.Arrays;
import java.util.concurrent.TimeUnit;

/**
 * 简单的单实例redis分布式锁
 * 没有实现的高级功能：锁的重入、锁的续约等
 *
 * @Author:tt
 * @Description:
 * @CreateTime:2019/6/12
 */
public class SingleRedisLock {

    private JedisPool jedisPool;

    /**
     * 获取锁
     *
     * @param lockKey          锁的key
     * @param lockVal          锁的val，可以利用来实现"避免误删别人锁"、"锁的重入"等功能
     * @param lockMaxLifeTime  锁的最大生命时长，到期自动销毁，单位：毫秒
     * @param tryWaitingTime   等待获取锁的超时时间，单位：毫秒
     * @param waitingSleepTime 等待获取锁的阻塞周期，单位：毫秒，设置过短会造成cpu竞争，设置过长会造成浪费，需依赖于'具体业务平均的执行时长'
     * @return
     */
    public Boolean tryLock(String lockKey, String lockVal, int lockMaxLifeTime, int tryWaitingTime, int waitingSleepTime) {

        //lua脚本，让逻辑简单清晰，同时保证原子性
        //setNX：成功-1，失败-0
        String lua = " if redis.call('set',KEYS[1],ARGV[1],'PX',ARGV[2],'NX') then return 1 else return 0 end ";

        //获取锁的开始时间
        Long tryBeginTime = System.currentTimeMillis();

        //轮询
        while (true) {

            Long result = null;
            Jedis jedis = null;
            try {
                jedis = jedisPool.getResource();
                result = (Long) jedis.eval(lua, Arrays.asList(lockKey), Arrays.asList(lockVal, String.valueOf(lockMaxLifeTime)));
            } catch (Exception e) {
                e.printStackTrace();
            } finally {
                if (jedis != null) {
                    try {
                        jedis.close();
                    } catch (Exception e) {
                    }
                }
            }

            //获取锁成功
            if (Long.valueOf(1).equals(result)) {
                return true;
            }

            //当前时间
            Long now = System.currentTimeMillis();
            //获取等待超时，就不用获取了
            if (now - tryBeginTime >= tryWaitingTime) {
                return false;
            }

            try {
                //阻塞等一会儿再重新去获取
                TimeUnit.MILLISECONDS.sleep(waitingSleepTime);
            } catch (InterruptedException e) {
            }

        }

    }

    /**
     * 释放锁
     *
     * @param lockKey
     * @param lockVal
     * @return
     */
    public void releaseLock(String lockKey, String lockVal) {

        //如果lockVal是自己的再删除，防止误删，场景来源：当前锁的持有者操作时间太长，锁已经自动释放并被别人占有了
        String lua = "if redis.call('get', KEYS[1]) == ARGV[1] then redis.call('del', KEYS[1]) end ";

        Jedis jedis = null;
        try {
            jedis = jedisPool.getResource();
            jedis.eval(lua, Arrays.asList(lockKey), Arrays.asList(lockVal));
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (jedis != null) {
                try {
                    jedis.close();
                } catch (Exception e) {
                }
            }
        }

    }

    //测试
    public static void main(String[] args) {
        //连接池
        JedisPool jedisPool = new JedisPool(new GenericObjectPoolConfig(), "127.0.0.1", 6379, 2000, "test123");
        SingleRedisLock simpleRedisLock = new SingleRedisLock();
        simpleRedisLock.jedisPool = jedisPool;

        //模拟10个并发
        for (int i = 0; i < 10; i++) {
            new Thread(() -> {

                String lockKey = "TEST_LOCK_KEY";
                String threadName = Thread.currentThread().getName();

                //获取锁
                Boolean locked = simpleRedisLock.tryLock(lockKey, threadName,
                        30000, 5000, 200);

                //获取锁失败
                if (!locked) {
                    System.err.println(">>> " + threadName + " 获取锁失败");
                    return;
                }

                //获取锁成功，模拟执行业务操作
                System.out.println(">>> " + threadName + " 获取锁成功");
                doShortBusiness();
                //doLongBusiness();

                //释放锁
                simpleRedisLock.releaseLock(lockKey, threadName);

            }).start();
        }

        try {
            TimeUnit.MILLISECONDS.sleep(60000);
        } catch (InterruptedException e) {
        }
    }

    //短任务：100毫秒
    static void doShortBusiness() {
        try {
            TimeUnit.MILLISECONDS.sleep(100);
        } catch (InterruptedException e) {
        }
    }

    //长任务：3秒
    static void doLongBusiness() {
        try {
            TimeUnit.MILLISECONDS.sleep(3000);
        } catch (InterruptedException e) {
        }
    }

}

Advanced features include lock re-entry lock, lock renewal, of course, in order to ensure high availability lock, redis there from the main deployment, clustering, etc., corresponding lock implementation is also different, slightly more complicated, but there are ready-made framework for our reference use, more well known as Redisson, a powerful redis client, of course, including "distributed lock" the perfect realization, which supports single-instance redis, Sentinel, clusters and other models.

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