redis分布式锁实现教程

分布式锁一般有三种实现方式：1. 数据库乐观锁；2. 基于Redis的分布式锁；3. 基于ZooKeeper的分布式锁。本篇博客将介绍第二种方式，基于Redis实现分布式锁。虽然网上已经有各种介绍Redis分布式锁实现的博客，然而他们的实现却有着各种各样的问题，为了避免误人子弟，本篇将介绍如何正确地实现Redis分布式锁。　

　　首先，为了确保分布式锁可用，我们至少要确保锁的实现同时满足以下四个条件：

1. 互斥性。在任意时刻，只有一个客户端能持有锁。
2. 不会发生死锁。即使有一个客户端在持有锁的期间崩溃而没有主动解锁，也能保证后续其他客户端能加锁。
3. 具有容错性。只要大部分的Redis节点正常运行，客户端就可以加锁和解锁。
4. 解铃还须系铃人。加锁和解锁必须是同一个客户端，客户端自己不能把别人加的锁给解了。 

感谢 myseries博主的教程。。

package com.gdut.redis.lock.test1;

import java.util.Collections;

import redis.clients.jedis.Jedis;
import redis.clients.jedis.JedisPool;

public class DistributedLock {
    private static final String LOCK_SUCCESS = "OK";
    private static final String SET_IF_NOT_EXIST = "NX";
    private static final String SET_WITH_EXPIRE_TIME = "PX";
    private static final Long RELEASE_SUCCESS = 1L;

    private static void validParam(JedisPool jedisPool, String lockKey, String requestId, int expireTime) {
        if (null == jedisPool) {
            throw new IllegalArgumentException("jedisPool obj is null");
        }

        if (null == lockKey || "".equals(lockKey)) {
            throw new IllegalArgumentException("lock key  is blank");
        }

        if (null == requestId || "".equals(requestId)) {
            throw new IllegalArgumentException("requestId is blank");
        }

        if (expireTime < 0) {
            throw new IllegalArgumentException("expireTime is not allowed less zero");
        }
    }

    /**
     * 
     * @param jedis
     * @param lockKey
     * @param requestId
     * @param expireTime
     * @return
     */
    public boolean tryLock(JedisPool jedisPool, String lockKey, String requestId, int expireTime) {

        validParam(jedisPool, lockKey, requestId, expireTime);

        Jedis jedis = null;
        try {

            jedis = jedisPool.getResource();
            String result = jedis.set(lockKey, requestId, SET_IF_NOT_EXIST, SET_WITH_EXPIRE_TIME, expireTime);

            if (LOCK_SUCCESS.equals(result)) {
                return true;
            }
        } catch (Exception e) {
            throw e;
        } finally {
            if (null != jedis) {
                jedis.close();
            }
        }

        return false;
    }

    /**
     * 
     * @param jedis
     * @param lockKey
     * @param requestId
     * @param expireTime
     */
    public void lock(JedisPool jedisPool, String lockKey, String requestId, int expireTime) {

        validParam(jedisPool, lockKey, requestId, expireTime);

        while (true) {
            if (tryLock(jedisPool, lockKey, requestId, expireTime)) {
                System.out.println("lock  "+ Thread.currentThread().getName()+ " requestId:" + requestId);
                return;
            }
        }
    }

    /**
     * 
     * @param jedis
     * @param lockKey
     * @param requestId
     * @return
     */
    public boolean unLock(JedisPool jedisPool, String lockKey, String requestId) {

        validParam(jedisPool, lockKey, requestId, 1);

        String script = "if redis.call('get', KEYS[1]) == ARGV[1] then return redis.call('del', KEYS[1]) else return 0 end";

        Jedis jedis = null;
        try {

            jedis = jedisPool.getResource();
            Object result = jedis.eval(script, Collections.singletonList(lockKey),
                    Collections.singletonList(requestId));

            if (RELEASE_SUCCESS.equals(result)) {
                System.out.println("unlock  "+ Thread.currentThread().getName()+ " requestId:" + requestId);
                return true;
            }

        } catch (Exception e) {
            throw e;
        } finally {
            if (null != jedis) {
                jedis.close();
            }
        }

        return false;

    }

}

package com.gdut.redis.lock.test1;

import java.util.UUID;

import com.gdut.redis.lock.test1.DistributedLock;

import redis.clients.jedis.JedisPool;
import redis.clients.jedis.JedisPoolConfig;

public class Service1 {
    private static JedisPool pool = null;
    private DistributedLock lock = new DistributedLock();
    
    static {
        JedisPoolConfig config = new JedisPoolConfig();
        // 设置最大连接数
        config.setMaxTotal(500);
        // 设置最大空闲数
        config.setMaxIdle(100);
        // 设置最大等待时间
        config.setMaxWaitMillis(1000 * 100);
        // 在borrow一个jedis实例时，是否需要验证，若为true，则所有jedis实例均是可用的
        config.setTestOnBorrow(true);
        pool = new JedisPool(config, "127.0.0.1", 6379, 300000);
    }
    
    public void seckill() throws InterruptedException {
        String requestId = UUID.randomUUID().toString();
        lock.lock(pool, "resource", requestId, 3000);
        lock.unLock(pool, "resource", requestId);
    }
}

package com.gdut.redis.lock.test1;

import com.gdut.redis.lock.test1.Service1;

public class TaskThread extends Thread {
    private Service1 service;
    
    public TaskThread(Service1 service) {
        this.service = service;
    }
    
    @Override
    public void run() {
        try {    
            synchronized (this) {
                service.seckill();
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    
    public static void main(String[] args) {
        Service1 service = new Service1();
        for (int i = 0; i < 400; i++) {
            TaskThread thread = new TaskThread(service);
            thread.start();
        }
    }

}