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CGImageSource and detecting corrupt images

I have an applications that reads images from a mounted volume or folder and then creates a thumbnail of the image to store in a catalogue using the CGImageSource functions. It is a Cocoa application, but I've partially written a wrapper around CGImageSource to provide it's functionality as an object.

My problem is that sometimes the image being read in is corrupt. This causes the execution to halt while I'm calling the function CGImageSourceCreateThumbnailAtIndex. More specifically it stops in the sub-routine Extract_LZW_Codes around the line:
0x91c768c8  <+0400>  vsrh v10,v10,v3

This part of the code is running in a seperate thread from the main application that is created to read in the image information.

CGImageSourceGetCount returns an image available within the image and CGImageSouceGetStatus returns 0, indicating that the image is valid and not corrupt. I am not interested in trying to recover the broken image - the ones I have tested cannot be opened by any image reading program I have (Preview, Photoshop), nor can finder show a preview of it.

I would like to be able to detect when a file cannot be read and somehow continue execution (after as time out period perhaps) - or at the very least terminate the thread, although this doesn't seem a trivial thing to do to an NSThread.

Thanks in advance, I'd appreciate any feedback on the matter, even if it's just directions to some related literature. I've been trying to work through this problem for weeks with no success, so anything at all would be useful.

--
Hayden
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