Gonzalo Ayuso has a new post to his site today showing how to create a TCP server daemon with PHP with help from the Ratchet toolset. Ratchet is a library that makes it easier to work with WebSockets directly from PHP.
In my daily work I normally play a lot with TCP servers, clients and things like that. I like to use Linux's xinet.d daemon to handle the TCP ports. I've also written something about it. This approach works fine. The problem appears when we call intensively our xinet.d server. It creates one PHP instance per request. It isn't a problem with one request in, for example, 3 seconds, but if we need to handle 10 requests per second our server load will grow. The solution: a dedicated server.
In a setup similar to how Silex registers callbacks, he's created a PHP-based server that listens on whatever ports are defined for incoming connections and processes the data accordingly. He includes several code samples that show it in use, both in simple request handling and more complex configurations based off of a YAML file definition. He ends the post with a method he uses to "emulate" threading in his processing with the help of a Silex app and HTTP requests to hand off the processed and remove the blocking problem PHP introduces.