stuck note prevention in midiator

# Make MIDIator cleanup at program termination:
class MIDIator::Driver
  alias orig_init initialize
  alias orig_note_on note_on
  alias orig_note_off note_off
  
  def initialize(*params)
    orig_init(*params)
    @held_notes = Hash.new {|hash,key| hash[key]={} }
    at_exit do
      @held_notes.each do |channel,notes|
        notes.each do |note,velocity|
          orig_note_off(note, channel, velocity)
        end
      end
      close
    end
  end  

  def note_on( note, channel, velocity )
    orig_note_on( note, channel, velocity )
    @held_notes[channel][note] = velocity
  end

  def note_off( note, channel, velocity = 0 )
    orig_note_off( note, channel, velocity )
    @held_notes[channel].delete(note)
  end
end