Garbage Collection Crash using NSImage

Question

This piece of code was split off from a project I am working on. It consistently reproduces a garbage collection error on my Mac OS 10.5.7 and sometimes crashes. I have been looking at it for too long so my question is: does anybody else see why this would give errors when garbage collection is on?

- (void) doCrash: (id) sender
{
    NSArray *lURLArray = [ NSArray arrayWithObjects:
                          @"http://userserve-ak.last.fm/serve/300x300/23621007.jpg",
                          @"http://userserve-ak.last.fm/serve/300x300/26675609.png",
                          @"http://userserve-ak.last.fm/serve/300x300/26675609.png",
                          nil ];
    NSString *lImageURL = nil;
    for (lImageURL in lURLArray)
    {
        NSImage *lImage = [[NSImage alloc] initWithContentsOfURL: [NSURL URLWithString: lImageURL]];

        NSSize targetSize = NSMakeSize(80,80);
        NSImage *newImage = [[NSImage alloc] initWithSize:targetSize];
        [newImage lockFocus];

        NSRect thumbnailRect = NSMakeRect(0,0,80,80);
        NSRect sourceRect = NSMakeRect(0,0,[lImage size].width,[lImage size].height);

        [lImage drawInRect: thumbnailRect
                  fromRect: sourceRect
                 operation: NSCompositeSourceOver
                  fraction: 1.0];                

        [newImage unlockFocus];
    }
}

When playing around with the URLs in the lURLArray I get different behavior: sometimes crashes, sometimes the error message.

The garbage collection error message is triggered when the garbage collector is freeing one of the images and goes like this:

reference count underflow for <address>, break on auto_refcount_underflow_error to debug.

Any help is much appreciated, thanks, Kristof

Answer 1

This has been confirmed to me by someone from Apple as a bug in OX X 10.5.7.

rdar://problem/6938657