How does redis solve the flash sale and overselling problem?

 public function kucun()
    {
        //有十个库存
        $count=10;
        //添加到redis list中
        for($i=0;$i<$count;$i++){
            Predis::getInstance()->lpush(&#39;kucun&#39;,111111111);
        }
        self::dd(Predis::getInstance()->lrange(&#39;kucun&#39;,0,-1));
    }

 public function ru()
    {   
        //判断计数器
        if (Predis::getInstance()->lpop('kucun')) {
            $user=User::where('user_id',1082)->find();
            //存入会员id
            Predis::getInstance()->lpush('user',$user['user_id']);
            //计数器累计加1
            // Predis::getInstance()->incr('number');
            echo '加入秒杀成功';exit();
        }else{
            echo '活动截至';
            exit();
        }
    }

ab -r -n 1000 -c 1000  http://149.28.16.212/index/index/ru