# File lib/generate_id.rb, line 11
  def initialize ( &already_exist )
    md5 = Digest::MD5::new
    id = ''
    begin
      md5.update(id)
      md5.update(Time.now.to_s)
      md5.update(rand.to_s)
      md5.update($$.to_s)
      md5.update($0)
      id = md5.hexdigest[0,16]
    end while block_given? and already_exist[id]
    id
  end