应用Redis实现分布式锁

主要参考：

1. http://blog.csdn.net/fjssharpsword/article/details/52250723#
2. http://www.yiibai.com/redis/strings_getset.html
3. https://redis.io/commands/expire
4. https://www.baidu.com/link?url=kuDPE2uEXfjZO3qCggv2OaDGcd9_Mohb_S2Web1VHiY623cg4IJZRwqb0_tGyan7x0BJuV1I46dh-qGWCPEJsa&wd=&eqid=879de37e00008ea500000004583ef0f8

package com.deppon.spring;

import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.RejectedExecutionHandler;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;

import redis.clients.jedis.Jedis;

/**
 *
 * @author ganxj
 *
 */
public class BuildDistributedLockWithRedisDB {
    // 锁名
    private static final String lockName = "lock";

    // 序列名
    private static final String sequenceName = "sequence";

    // 数据失效时间
    private static final int expired = 1;// 1秒超时

    // 当前线程处理当次缓存操作所需时间，(预估值)
    private static final int time = 10 * 1000;

    // setnx --- 当且仅当 key 不存在，将 key 的值设为 value ，并返回1；若给定的 key 已经存在，则 SETNX不做任何动作，并返回0。
    // getSet -- 将给定 key 的值设为 value ，并返回 key 的旧值 (old value)，当 key存在但不是字符串类型时，返回一个错误，当key不存在时，返回nil。
    // 上锁
    public static boolean acquireLock(Jedis jedis, String lock) {
        try {

            // 用于设置成功后的缓存处理时长
            long cacheProcessTime = System.currentTimeMillis() + time;

            // key为空时，争抢锁
            long isSetSuccessWhileKeyIsNil = jedis.setnx(lock, String.valueOf(cacheProcessTime));

            // SETNX成功，则成功获取一个锁，并设置数据失效时间
            if (isSetSuccessWhileKeyIsNil == 1) {
                jedis.expire(lock, expired);
                return true;
            }

            // key不为空，SETNX失败，说明锁被其他客户端保持，检查其是否已经超时
            String lastLockTimeBySomeThread = jedis.get(lock);

            // 如果获取key为空，则重走空key时的加锁流程
            if (lastLockTimeBySomeThread == null) {
                return false;
            }

            // 获取key不为空，则判断是否超时，若未超时，则循环重试
            if (Long.valueOf(lastLockTimeBySomeThread) > System.currentTimeMillis()) {
                return false;
            }

            // 若超时，则进行争抢加锁
            String getOldIfSet = jedis.getSet(lock, String.valueOf(cacheProcessTime));

            // 判断加锁是否成功
            if (getOldIfSet != null && getOldIfSet.equals(lastLockTimeBySomeThread)) {
                return true;
            }

            // 若加锁失败，重头再来
            return false;

        } catch (Exception e) {
            e.printStackTrace();
        }
        return false;
    }

    // 释放锁
    public static void releaseLock(Jedis jedis, String lock) {

        try {

            String lastLockTimeBySomeThread = jedis.get(lock);

            if (lastLockTimeBySomeThread == null) {
                return;
            }

            // 避免删除非自己获取得到的锁
            if (System.currentTimeMillis() < Long.valueOf(lastLockTimeBySomeThread)) {
                jedis.del(lock);
            }

        } catch (Exception e) {
            e.printStackTrace();
        }

    }

    @SuppressWarnings("resource")
    public static void main(String[] args) {

        // 任务数
        int produceTaskMaxNumber = 100;

        // 初始化redis中的id序列
        Jedis jedis = new Jedis();
        jedis.set(sequenceName, String.valueOf(Long.valueOf(1)));

        // 初始化线程池
        int corePoolSize = 20;
        int maximumPoolSize=20;
        long keepAliveTime =20;
        TimeUnit unit =TimeUnit.SECONDS;
        BlockingQueue<Runnable> workQueu = new ArrayBlockingQueue<Runnable>(30);
        RejectedExecutionHandler handler = new ThreadPoolExecutor.DiscardOldestPolicy();
        ThreadPoolExecutor threadPool = new ThreadPoolExecutor(
                corePoolSize,
                maximumPoolSize,
                keepAliveTime,
                unit,
                workQueu,
                handler);

        // 创建任务
        for (int i = 1; i <= produceTaskMaxNumber; i++) {
            try {
                threadPool.execute(new BuildDistributedLockWithRedisDB().new RedisLockTestTask());
            } catch (Exception e) {
                e.printStackTrace();
            }
        }

    }

    class RedisLockTestTask implements Runnable {

        @Override
        public void run() {

            Jedis jedis = new Jedis();
            Boolean lockFlag = true;

            // 循环等待拿锁
            long startTime = System.currentTimeMillis();
            while (lockFlag) {
                if (BuildDistributedLockWithRedisDB.acquireLock(jedis, lockName)) {
                    // 获得锁了，开始执行业务逻辑
                    process(jedis, sequenceName);
                    lockFlag = false;
                }
            }
            long endTime = System.currentTimeMillis();

            System.out.println(Thread.currentThread().getName()
                    + "线程设置的值:"
                    + jedis.get(sequenceName)
                    + "  "
                    + "共消耗时长：" + (endTime - startTime) + "ms");

            // 释放锁
            BuildDistributedLockWithRedisDB.releaseLock(jedis, lockName);

        }

    }

    void process(Jedis jedis,String sequenceName){
        jedis.set(sequenceName, String.valueOf(Long.valueOf(jedis.get(sequenceName)) + 1));
    }

}