Server.accept will block (wait) until a new connection happens. Once the callback (in the form of a Ruby block) completes the thread will end. So it starts a potentially infinite number of threads but only one per connection and each one is terminated pretty quickly. This is a pretty common way to write a server that can handle multiple simultaneous connections.

Soo the parameter to Thread.new is a function that blocks on the parent thread, before a new thread is even created?

Ruby (and most languages) evaluates the arguments before passing them through to the function. So it first evaluates server.accept, which blocks until a new connection, then passes the return value through to Thread.new which spawns the new thread.

The parameters to Thread.new are just passed straight through to the block.

Ahhh! I thought it was passing the accept function and not its result. Been too long, ruby! Thanks guys :)

Yep, that's exactly what's happening. A little confusing because ruby doesn't require brackets for zero argument function calls.