See:
Open Swoole: PHP Server with Async IO, Coroutines and Fibers (previously Swoole) | Open Swoole PHP
Use Open Swoole to build high-performance, scalable, concurrent TCP, UDP, Unix Socket, HTTP, WebSocket services with PHP without too much knowledge about non-blocking I/O programming and low-level Linux kernel with fiber and coroutines.
openswoole.com
PHP MQTT Server | Open Swoole PHP
Documentation of Open Swoole, Open Swoole Wiki, Open Swoole Tutorial
openswoole.com