code: public static void shutdownAll() {
  		for (final ExecutorService executor : new ArrayList<ExecutorService>(BACKGROUND_EXECUTORS)) {
  			shutdown(executor);
  			BACKGROUND_EXECUTORS.remove(executor);
  		}
  		for (final ScheduledExecutorService scheduler : new ArrayList<ScheduledExecutorService>(SCHEDULERS)) {
  			shutdown(scheduler);
  			SCHEDULERS.remove(scheduler);
  		}
  	}
docs: Shuts down all registered scheduler and background workers as soon as possible, but at the latest in specified
  {@link #SHUTDOWN_DURATION} seconds.