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);

      });

  }

}