Synchronized scope/performance confusion

Question

I have a servlet that takes the path to an image and the desired size and resizes it and writes it back out through the response.
In it there are a couple of lines that need to be throttled or the server quickly becomes overloaded when several people are looking at different pages of thumbnails that are being rendered from large images. To do this I started playing around with synchronizing them. This caused a larger then expected performance decrease for two methods and actually increased performance in the third. So the question is what on earth is the difference between the following three examples
//the servlets doPost do get calls doPost.
    protected void doPost(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, IOException {
         java2D(request, response);
EXAMPLE 1 - This was just horrible I understands it locks the whole method
     private synchronized void java2D(HttpServletRequest request, HttpServletResponse response) {
                        BufferedImage thumbImage = null; //the shrunken image
                        Image smallImage;
               Graphics2D g = thumbImage.createGraphics();
               g.drawImage(smallImage,0,0,null);
EXAMPLE 2 - This really did not behave any different then the above example.
     private void java2D(HttpServletRequest request, HttpServletResponse response) {
                        BufferedImage thumbImage = null; //the shrunken image
                        Image smallImage;
                   synchronized(this){
               Graphics2D g = thumbImage.createGraphics();
               g.drawImage(smallImage,0,0,null);
EXAMPLE 3 - This time I created a static inner class to do the work and it performs great (on our integration server). I am suspect that some how I am not preventing it from only being run once at a time but it seems that it should only run once as it is synchronized.
//The inner class
     static class ImageRender {
          public static synchronized void drawImage(BufferedImage thumbImage, Image smallImage) {
               Graphics2D g = thumbImage.createGraphics();
               g.drawImage(smallImage,0,0,null);
     private void java2D(HttpServletRequest request, HttpServletResponse response) {
                        BufferedImage thumbImage = null; //the shrunken image
                        Image smallImage;
               ImageRender.drawImage(thumbImage, smallImage);
         }Thanks for any discussion

Answer 1

The difference between 2) and 3) is what monitor it synchronizes on. In case 3) it synchronizes on the Class object representing the inner class. My guess is that something in your server's processes is synchronizing on the servlet instance (and is therefor being blocked).
Try creating a monitor just for this purpose as
private static Object monitor = new Object();
  synchronized(monitor) {
     Graphics2D g = thumbImage.createGraphics();
      g.drawImage(smallImage,0,0,null);
   }But you probably ought to consider being a bit more sophisticated, like allowing up to a certain number of these things to run simultaneously and, probably, caching the results.