redis如何解決秒殺超賣問題

 public function kucun()
 {
 //有十個庫存
 $count=10;
 //添加到redis list中
 for($i=0;$i<$count;$i++){
 Predis::getInstance()->lpush('kucun',111111111);
 }
 self::dd(Predis::getInstance()->lrange('kucun',0,-1));
 }

 public function ru()
 { 
 //判斷計數器
 if (Predis::getInstance()->lpop('kucun')) {
 $user=User::where('user_id',1082)->find();
 //存入會員id
 Predis::getInstance()->lpush('user',$user['user_id']);
 //計數器累計加1
 // Predis::getInstance()->incr('number');
 echo '加入秒殺成功';exit();
 }else{
 echo '活動截至';
 exit();
 }
 }

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