code: public static void shutdownNow() {
  		CachedScheduler oldElastic = CACHED_ELASTIC.getAndSet(null);
  		CachedScheduler oldParallel = CACHED_PARALLEL.getAndSet(null);
  		CachedScheduler oldSingle = CACHED_SINGLE.getAndSet(null);
  
  		if (oldElastic != null) oldElastic._dispose();
  		if (oldParallel != null) oldParallel._dispose();
  		if (oldSingle != null) oldSingle._dispose();
  	}
docs: Clear any cached {@link Scheduler} and call dispose on them.