# File lib/sup/thread.rb, line 252
  def initialize index, thread_by_subj=true
    @index = index
    @num_messages = 0
    ## map from message ids to container objects
    @messages = SavingHash.new { |id| Container.new id }
    ## map from subject strings or (or root message ids) to thread objects
    @threads = SavingHash.new { Thread.new }
    @thread_by_subj = thread_by_subj
  end