https://lwn.net/Articles/884833/
exit: Introduce __WCHILDSIGINFO for waitid [LWN.net]
exitintroducewaitidlwn
https://www.php.net/manual/ja/function.pcntl-waitid.php
PHP: pcntl_waitid - Manual
phppcntlwaitidmanual
https://www.php.net/manual/tr/function.pcntl-waitid.php
PHP: pcntl_waitid - Manual
Waits for a child process to change state
phppcntlwaitidmanual