# Notice the registered `ProgessionListener` that the operation progressed.
	#
	# Parameter:
	#
	# * `done_part`: Indicates what is done.
	# * `total`: Indicates what need to be done, `done_part` included.
	protected fun fire_progressed(done_part: Int, total: Int) do
		for l in progression_listeners do
			l.progressed(done_part * l.progression_max / total)
		end
	end