transient sclass ThumbnailCache {
  settable WidthAndHeightImpl thumbnailSize = new(100);
  
  // max bytes in memory
  settable long maxBytes = oneMegabyte();
  
  // estimated bytes in memory
  gettable long usedBytes;
  
  Q q = startQ();
  
  new TheMap map;
  
  transient Lock lock = lock();
  
  class TheMap extends LinkedHashMap<File, BufferedImage> {
    @Override
    protected bool removeEldestEntry(Map.Entry<File, BufferedImage> eldest) {
      if (usedBytes > maxBytes) {
        usedBytes -= guessImageBytes(eldest.getValue());
        true;
      }
      false;
    }
  }
  
  int guessImageBytes(BufferedImage image) {
    // 24 is a random guess for the overhead of an image
    ret 24+guessImageSizeInMemory(image);
  }
  
  BufferedImage makeThumbnail(File file) {
    var fullSize = loadImage2(file);
    ret scaleBufferedImageToMaxWidthOrHeight(thumbnailSize, fullSize);
  }
  
  selfType thumbnailSize(int wAndH) {
    ret thumbnailSize(new WidthAndHeightImpl(wAndH));
  }
  
  void get(File imageFile, IVF1<BufferedImage> onLoad) {
    lock lock;
    if (map.containsKey(imageFile))
      onLoad.get(map.get(imageFile));
    else
      q.add(-> {
        BufferedImage img = null;
        pcall {
          img = makeThumbnail(imageFile);
        }
        {
          lock lock;
          usedBytes += guessImageBytes(img);
          map.put(imageFile, img);
        }
        onLoad.get(img);
      });
  }
}