Getting idle time in linux

For a little alarm prog I’m writing to help myself out with my polyphasic sleep endeavor I needed to get the idle time of an X session, the length of time since the user last used the mouse or keyboard. I searched for a while and there were a few people asking about it but no answers.

So I hacked around and found a simple way to do it in C. This requires you have the Xss (Xscreensaver, not cross site scripting :P) library and includes. (ubuntu: sudo apt-get install libxss-dev)

I wrote this on linux but in theory it should work in any unix X environment with libXss.

#include <X11/extensions/scrnsaver.h>

main() {
  XScreenSaverInfo *info = XScreenSaverAllocInfo();
  Display *display = XOpenDisplay(0);

  XScreenSaverQueryInfo(display, DefaultRootWindow(display), info);
  printf("%u ms\n", info->idle);
}

Compile with: gcc -o idle idle.c -lXss

And here’s a simple Ruby wrapper for it using RubyInline:

require 'inline'

class XScreenSaver
  class << self
    inline do |builder|
      builder.add_link_flags '-lXss'
      builder.include '<X11/extensions/scrnsaver.h>'
      builder.c %{
        double idle_time() {
          static Display *display;
          XScreenSaverInfo *info = XScreenSaverAllocInfo();

          if (!display)  display = XOpenDisplay(0);
          if (!display)  return -1;

          XScreenSaverQueryInfo(display, DefaultRootWindow(display), info);

          return info->idle / 1000.0;
        }
      }
    end
  end
end

if __FILE__ == $0
  loop { puts XScreenSaver.idle_time; sleep 0.2 }
end

Does anyone know a better way to do it?