Asynchronous PHP refers to PHP code that is written using the asynchronous model. In other words, asynchronous applications can multi-task. This is critical because traditionally, there’s a lot of time when a CPU sits idle while a PHP application manages I/O tasks. Not only does this slow overall application performance, but also, it lowers hardware utilization.
There are a few other choices for the PHP community to adopt async PHP:
React PHP - ReactPHP is a low-level library for event-driven programming in PHP. At its core is an event loop, on top of which it provides low-level utilities, such as Streams abstraction, async DNS resolver, network client/server, HTTP client/server and interaction with processes. Third-party libraries can use these components to create async network clients/servers and more.
AMP PHP - Amp is an event-driven concurrency framework for PHP providing primitives to manage cooperative multitasking building upon an event loop, and promises.
PHP 8.1 Fibers - For most of PHP’s history, people have written PHP code only as synchronous code. Execution of functions stops until a result is available to return from the function, including for I/O operations, which can be quite slow. More recently, there have been multiple projects that have allowed people to write asynchronous PHP code to allow for concurrent I/O operations. Asynchronous functions accept a callback or return a placeholder for a future value (such as a promise) to run code at a future time once the result is available. Execution continues without waiting for a result. Examples of these projects are amphp, ReactPHP, and Guzzle.
Workerman - An asynchronous event-driven PHP socket framework. Supports HTTP, Websocket, SSL and other custom protocols. PHP>=5.3.