Redis 缓存淘汰策略和事务实现乐观锁详情

multi

exec

discard

watch key [key…]

unwatch

127.0.0.1:6379> multi
OK
127.0.0.1:6379> set s1 111
QUEUED
127.0.0.1:6379> hset set1 name zhangsan
QUEUED
127.0.0.1:6379> exec
1) OK
2) (integer) 1
127.0.0.1:6379> multi
OK
127.0.0.1:6379> set s2 222
QUEUED
127.0.0.1:6379> hset set2 age 20
QUEUED
127.0.0.1:6379> discard
OK
127.0.0.1:6379> exec (error) ERR EXEC without MULTI 
127.0.0.1:6379> watch s1
OK
127.0.0.1:6379> multi
OK
127.0.0.1:6379> set s1 555
QUEUED 127.0.0.1:6379> exec # 此时在没有exec之前，通过另一个命令窗口对监控的s1字段进行修改 
(nil)
127.0.0.1:6379> get s1
111

public void watch() {
	try {
		String watchKeys = "watchKeys";
		//初始值 value=1
		jedis.set(watchKeys, 1);
		//监听key为watchKeys的值
		jedis.watch(watchkeys);
		//开启事务
		Transaction tx = jedis.multi();
		//watchKeys自增加一
		tx.incr(watchKeys);
		//执行事务，如果其他线程对watchKeys中的value进行修改，则该事务将不会执行
		//通过redis事务以及watch命令实现乐观锁
		List<Object> exec = tx.exec();
		if (exec == null) {
			System.out.println("事务未执行");
		} else {
			System.out.println("事务成功执行，watchKeys的value成功修改");
		}
	} catch (Exception e) {
		e.printStackTrace();
	} finally {
		jedis.close();
	}
}

public class RedisLock {
    public static void main(String[] arg) {
        //库存key 
        String redisKey = "stock";
        ExecutorService executorService = Executors.newFixedThreadPool(20);
        try {
            Jedis jedis = new RedisProperties.Jedis("127.0.0.1", 6378);
            // 可以被秒杀的库存的初始值，库存总共20个
            jedis.set(redisKey, "0");
            jedis.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
        for (int i = 0; i < 1000; i++) {
            executorService.execute(() -> {
                Jedis jedis1 = new Jedis("127.0.0.1", 6378);
                try {
                    jedis1.watch(redisKey);
                    String redisValue = jedis1.get(redisKey);
                    int valInteger = Integer.valueOf(redisValue);
                    String userInfo = UUID.randomUUID().toString();
                    // 没有秒完
                    if (valInteger < 20) {
                        Transaction tx = jedis1.multi();
                        tx.incr(redisKey);
                        List list = tx.exec();
                        // 秒成功 失败返回空list而不是空
                        if (list != null && list.size() > 0) {
                            System.out.println("用户：" + userInfo + "，秒杀成 功！当前成功人数：" + (valInteger + 1));
                        }
                        // 版本变化，被别人抢了。
                        else {
                            System.out.println("用户：" + userInfo + "，秒杀失 败");
                        }
                    }
                    // 秒完了
                    else {
                        System.out.println("已经有20人秒杀成功，秒杀结束");
                    }
                } catch (Exception e) {
                    e.printStackTrace();
                } finally {
                    jedis1.close();
                }
            });
        }
        executorService.shutdown();
    }
}