code: @SuppressWarnings("unchecked")
  	public synchronized <T> List<T> getExistingInstances(Key<T> key) {
  		checkState(injector != null && poolScope != null, "WorkerPool has not been initialized, make sure Boot module and ServiceGraph is used");
  		checkArgument(injector.getExistingBinding(key) != null, "Binding for %s not found", key);
  		return (List<T>) pool.get(key);
  	}
docs: endregion