def load_n_threads num, opts={}
    @index.each_id_by_date opts do |mid, builder|
      break if size >= num unless num == -1
      next if contains_id? mid

      m = builder.call
      load_thread_for_message m, :skip_killed => opts[:skip_killed], :load_deleted => opts[:load_deleted], :load_spam => opts[:load_spam]
      yield size if block_given?
    end
  end
def load_n_threads num, opts={}
    @index.each_id_by_date opts do |mid, builder|
      break if size >= num unless num == -1
      next if contains_id? mid

      m = builder.call
      load_thread_for_message m, :skip_killed => opts[:skip_killed], :load_deleted => opts[:load_deleted], :load_spam => opts[:load_spam]
      yield size if block_given?
    end
  end
load in (at most) num number of threads from the index