Re: NSCache objects not being collected under GC?
Re: NSCache objects not being collected under GC?
- Subject: Re: NSCache objects not being collected under GC?
- From: "email@hidden" <email@hidden>
- Date: Fri, 19 Aug 2011 09:40:37 +0100
On 19 Aug 2011, at 03:26, Nick Zitzmann wrote:
> Short version: Have any of you ever used NSCache in a GC-enabled app? If so, then how did you get the garbage collector to collect them?
>
> Long version: I have a framework that is used in a traditional retain-release app and a different GC-enabled app. The framework creates NSCache objects for storage of throw-away objects, and stores these NSCache objects in a CFDictionaryRef. At some point, the CFDictionaryRef is instructed to remove the entire cache when the app no longer needs that cache.
>
> That pops the NSCache and deallocates it in the retain-release app, but in the GC app, I ran an Instruments test and found that the NSCache objects and their contents were never being finalized. If I change the code so the code uses NSMutableDictionary instead of NSCache, then the dictionaries and their objects are properly finalized when popped. I want to use NSCache and not NSMutableDictionary, but I can't do this in the GC-enabled app if the collector is going to let the caches live forever. How do I make it so that the collector collects them?
>
> I already tried using Instruments to monitor the GC object graph, but the results made no sense. According to Instruments, the NSCache objects were rooted by a non-object memory address created before main() was called, a long time before the objects were made. Also, I noticed that objects in the cache would not identify the cache as their root. (Is that normal?)
I don't use NSCache but I have used instruments to effectively debug GC memory collection problems.
The described rooting behaviour of NSCache sounds peculiar to me.
What happens if you call -removeAllObjects. Are the cached objects finalised correctly?
I know this isn't the same as collecting the NSCache instance but at least, as a workaround if the issue persists, you can recycle the NSCache instances.
Regards
Jonathan Mitchell
Developer
Mugginsoft LLP
http://www.mugginsoft.com_______________________________________________
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