docker-php-fpm/php_modules/sysvmsg/README.md

sysvmsg

These modules provide wrappers for the System V IPC family of functions. It includes semaphores, shared memory and inter-process messaging (IPC).

Semaphores may be used to provide exclusive access to resources on the current machine, or to limit the number of processes that may simultaneously use a resource.

Platform	Url
PHP.net	https://www.php.net/manual/en/book.sem.php
Class	https://www.php.net/manual/en/class.sysvmessagequeue.php