title: Why is Node.js single threaded?
body: <p>In PHP (or Java/ASP.NET/Ruby) based webservers every client request is instantiated on a new thread. But in Node.js all the clients run on the same thread (they can even share the same variables!) I understand that I/O operations are event-based so they don't block the main thread loop.</p>
  
  <p>What I don't understand is WHY the author of Node chose it to be single-threaded? It makes things difficult. For example, I can't run a CPU intensive function because it blocks the main thread (and new client requests are blocked) so I need to spawn a process (which means I need to create a separate JavaScript file and execute another node process on it). However, in PHP cpu intensive tasks do not block other clients because as I mentioned each client is on a different thread. What are its advantages compared to multi-threaded web servers?</p>
  
  <p>Note: I've used clustering to get around this, but it's not pretty.</p>