How can I run PHP code asynchronously without waiting? I have a long run (almost infinite) that should run while server starts and should process asynchronously without wait
This isn't really what PHP is designed for. You have to use the PECL threading library to spin off threads that run asynchronously, and I don't recommend it. The new hotness in the async department is node.js - I recommend you look into that and see if you can utilize it. It's designed for light weight, asynchronous network operations, and can be used to fire PHP scripts.