GC and CF collections

[Jim Correia]

On Jul 6, 2008, at 9:51 AM, Christiaan Hofman wrote:

> One situation is if I just want to retain the objects, in which case  
> I usually make use of the standard kCFType...Callbacks. However  
> those use CFRetain/CFRelease AFAIK. So it seems to me that they  
> would basically make the objects I store uncollectable. Is that  
> correct? If so, should I use some custom callbacks using -retain/- 
> release? Or are the CFType...Callbacks now able to enable proper  
> garbage collection?

As long as the collection has a reference to the object it is not  
collectable. This is the usual use case (where you'd use the standard  
callbacks) and works correctly. If you have more complex needs, you  
need a different solution.

> Another use is a static CFMutableDictionaryRef to track simulated  
> ivars. This means that I register pairs of an object and a simulated  
> ivar, using the object as key and the simulated ivar as value. The  
> keyCallbacks for the dictionary are trivial, because otherwise the  
> object used as key will never be deallocated (and this is the main  
> reason I'm using CFMutableDictionary). This works great with managed  
> memory.
>
> However I wonder now if this can work with GC. Is the garbage  
> collector able to clean up the object, even if it is referenced as a  
> key by the CFMytableDictionary?

You should consider migrating your special needs code which uses CF  
collections with custom callbacks to NSMapTable and NSPointerArray in  
your GC-savvy code. It has options for strong or weak objects or keys,  
and does the correct thing with respect to GC and write barriers.

Jim