Cocoa Memory Usage

Question

I'm trying to track down some peculiar memory behavior in my Cocoa desktop app. My app does a lot of image processing using NSImage and uploads those images to a website over HTTP using NSURLConnection.

After uploading several hundred images (some very large), when I run Instrument I get no leaks. I've also run through MallocDebug and get no leaks. When I dig into object allocations using Instrument I get output like this:

GeneralBlock-9437184, Net Bytes 9437184, # Net 1
GeneralBlock-192512, Net Bytes 2695168, # Net 14

and etc., for smaller sizes. When I look at these in detail, they're marked as being owned by 'Foundation' and created via NSConcreteMutableData initWithCapacity. During HTTP upload I'm creating a post body using NSMutableData, so I'm guessing these are buffers Cocoa is caching for me when I create the NSMutableData objects.

Is there a way to force Cocoa to free these? I'm 90% positive I'm releasing correctly (and Instruments and MallocDebug seem to confirm this), but I think Cocoa is keeping these around for perf reasons since I'm allocating so many MSMutableData buffers.

Answer 1

If you're certain you're releasing the objects you own correctly, then there's really nothing you can (or should) do. Those blocks are, as Instruments says, owned by Foundation because NSConcreteMutableData, a Foundation object, created them. It's possible that these are some sort of cache that NSData is keeping around on purpose, but there's no way to know what they are.

If you believe this is a bug, you should report it at http://bugreport.apple.com. The rules of memory ownership apply to classes that don't manage memory well, too.

Also, this might be a silly question, but which option are you using for the Object Alloc tool? All objects created or Created and still living? You might be looking at allocations that don't matter anymore.