require 'alib'

def dir_size dir
  size = 0
  visited = {}
  ALib::Util::find2(dir, 'follow' => true) do |path, stat|
    begin
      next if visited[stat.ino]
      next unless stat.file?
      size += stat.size
    ensure
      visited[stat.ino] = true 
    end
  end
  size
end

p dir_size('.')