Poll for different scheduler events like: there are tasks to run, there are tasks to postpone
		there are postponed tasks that should be running

		:return: None

def _polling_iteration(self):
		""" Poll for different scheduler events like: there are tasks to run, there are tasks to postpone
		there are postponed tasks that should be running

		:return: None
		"""
		scheduled_tasks = self.__sources_registry.check()
		has_postponed_tasks = self.__postponed_record_registry.has_records()
		maximum_tasks = self.maximum_running_records()

		if scheduled_tasks is not None or has_postponed_tasks is not None:
			running_tasks = len(self.__running_record_registry)

			if running_tasks >= maximum_tasks:
				if scheduled_tasks is not None:
					for task in scheduled_tasks:
						self.__postponed_record_registry.postpone(task)
			else:
				if has_postponed_tasks is True:
					for postponed_task in self.__postponed_record_registry:
						self.__running_record_registry.exec(postponed_task)
						running_tasks += 1
						if running_tasks >= maximum_tasks:
							break

				if scheduled_tasks is not None:
					for task in scheduled_tasks:
						if running_tasks >= maximum_tasks:
							self.__postponed_record_registry.postpone(task)
						else:
							self.__running_record_registry.exec(task)
							running_tasks += 1