code: func (imageManager *dockerImageManager) RemoveContainerReferenceFromImageState(container *apicontainer.Container) error {
  	// the image state has been updated, save the new state
  	defer imageManager.saver.ForceSave()
  	// this lock is for reading image states and finding the one that the container belongs to
  	imageManager.updateLock.RLock()
  	defer imageManager.updateLock.RUnlock()
  	if container.ImageID == "" {
  		return fmt.Errorf("Invalid container reference: Empty image id")
  	}
  
  	// Find image state that this container is part of, and remove the reference
  	imageState, ok := imageManager.getImageState(container.ImageID)
  	if !ok {
  		return fmt.Errorf("Cannot find image state for the container to be removed")
  	}
  	// Found matching ImageState
  	return imageState.RemoveContainerReference(container)
  }
docs: // RemoveContainerReferenceFromImageState removes container reference from the corresponding imageState object