# File lib/cabin/channel.rb, line 118
  def subscribe(output)
    # Wrap ruby stdlib Logger if given.
    if output.is_a?(::Logger)
      output = Cabin::Outputs::StdlibLogger.new(output)
    elsif output.is_a?(::IO)
      output = Cabin::Outputs::IO.new(output)
    end
    @subscriber_lock.synchronize do
      @subscribers[output.object_id] = output
    end
    return output.object_id
  end