redis学习(二十三)

redis学习(二十三)

分布式锁

  运行效果如下图所示。从图中可以看出,同一个资源在同一个时刻只能被一个线程获取,从而保证了库存数量N的递减是顺序的。

接口

package com.cxy.redis.distributed;

/**
 * @program: redis
 * @description: 分布式锁,接口。
 * @author: cuixy
 * @create: 2020-08-13 16:23
 **/
public interface DistributedLock {

    //锁标示
    String acquire();

    //释放锁
    boolean release(String indentifier);

}

实现类

package com.cxy.redis.distributed;

import lombok.extern.slf4j.Slf4j;
import redis.clients.jedis.Jedis;

import java.util.Collections;
import java.util.UUID;

/**
 * @program: redis
 * @description: 分布式锁,实现类。
 * @author: cuixy
 * @create: 2020-08-13 16:28
 **/
@Slf4j
public class RedisDistributedLock implements DistributedLock {

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


    /**
     * redis 客户端
     */
    private Jedis jedis;

    /**
     * 分布式锁的键值
     */
    private String lockKey;

    /**
     * 锁的超时时间 10s
     */
    int expireTime = 10 * 1000;

    /**
     * 锁等待,防止线程饥饿
     */
    int acquireTimeout = 1 * 1000;

    /**
     * 获取指定键值的锁
     *
     * @param jedis   jedis Redis客户端
     * @param lockKey 锁的键值
     */
    public RedisDistributedLock(Jedis jedis, String lockKey) {
        this.jedis = jedis;
        this.lockKey = lockKey;
    }

    /**
     * 获取指定键值的锁,同时设置获取锁超时时间
     *
     * @param jedis          jedis Redis客户端
     * @param lockKey        锁的键值
     * @param acquireTimeout 获取锁超时时间
     */
    public RedisDistributedLock(Jedis jedis, String lockKey, int acquireTimeout) {
        this.jedis = jedis;
        this.lockKey = lockKey;
        this.acquireTimeout = acquireTimeout;
    }

    /**
     * 获取指定键值的锁,同时设置获取锁超时时间和锁过期时间
     *
     * @param jedis          jedis Redis客户端
     * @param lockKey        锁的键值
     * @param acquireTimeout 获取锁超时时间
     * @param expireTime     锁失效时间
     */
    public RedisDistributedLock(Jedis jedis, String lockKey, int acquireTimeout, int expireTime) {
        this.jedis = jedis;
        this.lockKey = lockKey;
        this.acquireTimeout = acquireTimeout;
        this.expireTime = expireTime;
    }


    @Override
    public String acquire() {
        try {
            //获取锁的超时时间,超过这个时间则放弃获取锁。
            long end = System.currentTimeMillis() + acquireTimeout;
            //随机生成一个value
            String requireToken = UUID.randomUUID().toString();
            while (System.currentTimeMillis() < end) {
                String result = jedis.set(lockKey, requireToken, SET_IF_NOT_EXIST, SET_WITH_EXPIRE_TIME, expireTime);
                if (LOCK_SUCCESS.equals(result)) {
                    return requireToken;
                }
                try {
                    Thread.sleep(100);
                } catch (InterruptedException e) {
                    Thread.currentThread().interrupt();
                }
            }

        } catch (Exception e) {

        }

        return null;
    }

    @Override
    public boolean release(String identify) {
        if (identify == null) {
            return false;
        }

        String script = "if redis.call('get', KEYS[1]) == ARGV[1] then return redis.call('del', KEYS[1]) else return 0 end";
        Object result = new Object();
        try {
            result = jedis.eval(script, Collections.singletonList(lockKey),
                    Collections.singletonList(identify));
            if (RELEASE_SUCCESS.equals(result)) {
                log.info("release lock success, requestToken:{}", identify);
                return true;
            }
        } catch (Exception e) {
            log.error("release lock due to error", e);
        } finally {
            if (jedis != null) {
                jedis.close();
            }
        }

        log.info("release lock failed, requestToken:{}, result:{}", identify, result);
        return false;
    }

}

测试类

package com.cxy.redis.distributed;

import redis.clients.jedis.Jedis;

/**
 * @program: redis
 * @description: 分布式锁测试类。
 * @author: cuixy
 * @create: 2020-08-13 17:01
 **/
public class RedisDistributedLockTest {

    static int n = 500;

    public static void secskill() {
        System.out.println(--n);
    }

    public static void main(String[] args) {

        for (int i = 0; i < 10; i++) {
            new Thread(() -> {
                RedisDistributedLock lock = null;
                String unLockIdentify = null;
                try {
                    Jedis conn = new Jedis("192.168.106.129", 6666);
                    //如果没有密码,就可以省略下面步骤。
                    conn.auth("cxy0809.");

                    lock = new RedisDistributedLock(conn, "test1");
                    unLockIdentify = lock.acquire();
                    System.out.println(Thread.currentThread().getName() + "正在运行");
                    secskill();
                } finally {
                    if (lock != null) {
                        lock.release(unLockIdentify);
                    }
                }
            }).start();
        }


    }

}