defmodule Foo do
  defmacro __using__(_) do
      quote do
       if Module.get_attribute(__MODULE__, :already_done) do
        IO.inspect "already done"
       else
        IO.inspect "doing"
          @already_done true
      end
   end
  end
end

defmodule Bar do
  use Foo
  use Foo
  use Foo
end