Question

I’m writing a snake game for the terminal, i.e. output via print.

The following works just fine:

while status[snake_monad] do
  print to_string draw canvas, compose_all([
    frame,
    specs,
    snake_to_hash(snake[snake_monad])
  ])

  turn! snake_monad, get_dir
  move! snake_monad, specs

  sleep 0.25
end

But I don’t want the turn!ing to block, of course. So I put it into a new Thread and let it loop:

Thread.new do
  loop do
    turn! snake_monad, get_dir
  end
end

while status[snake_monad] do
  ...
  # no turn! here
  ...
end

Which also works logically (the snake is turning), but the output is somehow interspersed with newlines. As soon as I kill the input thread (^C) it looks normal again.

So why and how does the thread have any effect on my output?
And how do I work around this issue?
(I don’t know much about threads, even less about them in ruby. Input and output concurrently on the same terminal make the matter worse, I guess…)

Also (not really important): Wanting my program as pure as possible, would it be somewhat easily possible to get the input non-blockingly while passing everything around?

Thank you!

Answer 1

You don’t want non-blocking IO – you want unbuffered IO.

There’s no need for threads, here – you just need to put your terminal into the right mode and then wait for the keypress on the main event loop.

Here’s a completely ridiculous example.

require 'io/wait'

def ping
  term = `stty -g`
  `stty raw -echo cbreak`
  loop do
    if STDIN.ready?
      #command thy snake!
      ret = STDIN.getc 
    end
    if ret
      #process the snake command if there was one
      STDOUT.write("you told the snake to #{ret}\n")
    else
      #slither around bitin' fools and hustling apples.
    end
  end
ensure
  `stty #{term}`
end