Re: EXC_BAD_ACCESS when -fobjc-gc is on (Was: Memory corruption ...)

[Gabriel Zachmann]

Thanks for the quick response.

I am still a bit confused ... and, besides, I still get a core dump ;-(

I think this is your problem right here. In a GC environment CALayer
isn't going to retain its content, it stores a strong reference
instead.

In the doc of CALayer.contents it says

   @property(retain) id contents




I tried this


  // [snip]
   imgLayer.contents = (id) cgImage;
  // [snip]
   CGImageRelease( cgImage );
   return imgLayer;

and this:


  // [snip]
   imgLayer.contents = (id) cgImage;
  // [snip]
   CFMakeCollectable( cgImage );
   return imgLayer;

Both yield the same crash at the same place.

Did I misunderstand something?

Or is the bug somewhere else?

First of all, how can I know that? (I'm asking so that I can avoid such bugs in the future) Does a retained property always translate to a strong reference in a GC environment? CGImageRef cgImage = CFMakeCollectable ( CGImageSourceCreateImageAtIndex( sourceRef, 0, NULL ) ); CGImageRef cgImage = CGImageSourceCreateImageAtIndex( sourceRef, 0, NULL ); In the guide it says that CFMakeCollectable() does a CFRelease() -- is that the same as a CGImageRelease() ?

But cgImage isn't collectable, so the strong reference does
nothing. Look at the documentaiton for CFMakeCollectable.

I did that and there is one sentence that I don't understand at all:



Shouldn't that be "a no-op in a GC environment." ?

Best regards,
Gabriel.

"CFMakeCollectable calls CFRelease, but has two supplementary features: [...]; second, it’s a no-op in a reference counted environment."

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