Laravel mysql Counter code

Counter.php

    /**
     * @param $tag
     * @param int $num
     * @return int|mixed
     */
    public static function incr($tag, $num = 1)
    {
        if ($num < 1) {
            throw new \Exception('num err');
        }
        // const TAG_MAX_LEN = 64;
        if (strlen($tag) > self::TAG_MAX_LEN) {
            throw new \Exception('tag too long');
        }

        $db = CounterModel::query()->getConnection();
        try {
            $db->beginTransaction();

            $counter = CounterModel::where('tag', $tag)->lockForUpdate()->first();
            if (!$counter) {
                try {
                    // 不存在则创建
                    // todo 这里没有处理两个创建冲突的情况，可以用tag的唯一索引来代替
                    CounterModel::create(['tag' => $tag, 'num' => 0]);
                    $counter = CounterModel::where('tag', $tag)->lockForUpdate()->first();
                } catch (\PDOException $PDOException) {
                    // SQLSTATE[40001]: Serialization failure: 1213 Deadlock found when trying to get lock; try restarting transaction
                    if (strpos($PDOException->getMessage(), 'Deadlock') === false) {
                        throw $PDOException;
                    }
                    // 如果创建失败，就用其他事务创建的
                    // 等待其他事务完成创建
                    sleep(1);
                    $counter = CounterModel::where('tag', $tag)->lockForUpdate()->first();
                    if (!$counter) {
                        throw new \Exception('放弃创建，但还是读不到数据');
                    }
                }
            }

            if ($counter) {
                $counter->num = $counter->num + $num;
                if ($counter->num > self::NUM_MAX_MYSQL) {
                    // const NUM_MAX_MYSQL = 255 * 255 * 255 * 255;
                    throw new \Exception('递增达到数据库最大值');
                }
                $counter->save();
                $result = $counter->num;
            }

            $db->commit();
        } catch (\Exception $exception) {
            $db->rollBack();
            throw $exception;
        }

        return $result;
    }