How can I prevent the MediaTracker waitForID method from blocking?
Hi everyone:
I am writing an application that deals with various image file formats with the help of the JIMI package (available at http://java.sun.com/products/jimi/). Everything works fine except for the Targa format. When I generate an Image object as follows (url is a valid URL object):
Image image = Jimi.getImage(url);
ImageIcon icon =new ImageIcon(image);
the program execution blocks at the second line above. I searched the ImageIcon source code for some clues, which led me to the following ImageIcon method (tracker is a MediaTracker object, a static property of ImageIcon):
(01)protectedvoid loadImage(Image image){
(02)synchronized(tracker){
(03)tracker.addImage(image, 0);
(04)try{
(05)tracker.waitForID(0, 0);
(06)}catch (InterruptedException e){
(07)System.out.println("INTERRUPTED while loading Image");
(08)}
(09)loadStatus = tracker.statusID(0,false);
(10)tracker.removeImage(image, 0);
(11)
(12)width = image.getWidth(imageObserver);
(13)height = image.getHeight(imageObserver);
(14)}
(15)}
The program blocks at line (05) above. I peeked into the MediaTracker class source code, which brought me to determine that the image loading process never finishes. The symptoms are as follows:
(1) When I perform a c.checkImage(image, null) where c is some Component, I always get a result of 7, which translates to the following combination of ImageObserver constants:
WIDTH | HEIGHT | PROPERTIES
As matter of fact, the dimensions are indeed determined correctly. However, when the loading process terminates, the checkImage result includes ALLBITS or FRAMEBITS in case of success, ABORT or ERROR in case of failure. None of these bits is ever turned on whenever I try to load a Targa image.
(2) When I get to the MediaTracker source code, I see that when none of the four bytes above is set, the internal MediaTracker status has the MediaTracker.LOADING bit turned on (nothing abnormal here). And the waitForID method terminates precisely only when this bit is turned off!
Logically, if the loading process fails for some reason, I should expect to get an error response so that I can go further in code execution. However, since the loading process never terminates, everything stays blocked at the waitForID method invocation.
Is there an efficient way to detect such a hidden loading error without letting my program go into the waitForID endless loop? In other words, going back to the first two lines of code of this message, how could I detect that an Image loading process will not terminate before calling the ImageIcon constructor?
Thanks in advance for any useful help...
Jean-Franois Morin
