https://blog.toright.com/posts/3639/php-%e5%88%a9%e7%94%a8-ignore_user_abort-pcntl_fork-%e5%af%a6%e4%bd%9c%e8%83%8c%e6%99%af%e5%9f%b7%e8%a1%8c-%e4%be%86%e4%be%86%e5%93%a5%e7%af%84%e4%be%8b