code: @Override
  	public boolean registerTaskManager(final ResourceID resourceID) {
  
  		componentMainThreadExecutor.assertRunningInMainThread();
  
  		log.debug("Register new TaskExecutor {}.", resourceID);
  		return registeredTaskManagers.add(resourceID);
  	}
docs: Register TaskManager to this pool, only those slots come from registered TaskManager will be considered valid.
  Also it provides a way for us to keep "dead" or "abnormal" TaskManagers out of this pool.
  
  @param resourceID The id of the TaskManager