Cache thousands of images - objective-c

Question

I've been developing a music player recently, I'm writing my own pickers.
I'm trying to test my code to it's limits, so I have around 1600 albums in my iPhone.
I'm using AQGridView for albums view, and since MPMediaItemArtwork is a subclass of NSObject, you need to fire up a method on it to get an image from it, and that method scales images.
Scaling for each cell uses too much CPU as you can guess, so my grid album view is laggy, despite all my effort manually driving each cell's includes.
So I thought of start scaling with GCD on app launch, then save them to file, and read that file for each cell.
But, my code
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^ {
MPMediaQuery *allAlbumsQuery = [MPMediaQuery albumsQuery];
NSArray *albumsArray = allAlbumsQuery.collections;
for (MPMediaItemCollection *collection in albumsArray) {
#autoreleasepool {
MPMediaItem *currentItem = [collection representativeItem];
MPMediaItemArtwork *artwork = [currentItem valueForProperty:MPMediaItemPropertyArtwork];
UIImage *artworkImage = [artwork imageWithSize:CGSizeMake(90, 90)];
if (artworkImage) [toBeCached addObject:artworkImage];
else [toBeCached addObject:blackImage];
NSLog(#"%#", [currentItem valueForProperty:MPMediaItemPropertyAlbumTitle]);
artworkImage = nil;
}
}
dispatch_async(dispatch_get_main_queue(), ^{
[[NSUserDefaults standardUserDefaults] setObject:[NSKeyedArchiver archivedDataWithRootObject:albumsArray] forKey:#"covers"];
});
NSLog(#"finished saving, sir");
});
in AppDelegate's application:didFinishLaunchingWithOptions: method makes my app crash, without any console log etc.
This seems to be a memory problem, so many images are kept in NSArray which is stored on RAM until saving that iOS force closes my app.
Do you have any suggestions on what to do?
Cheers

Answer 1

Take a look at the recently-released SYCache, which combines NSCache and on-disk caching. It's probably a bad idea to get to a memory-warning state as soon as you launch the app, but that's better than force closing.
As far as the commenter above suggested, mapped data is a technique (using mmap or its equivalent) to load data from disk as if it's all in memory at once, which could help with UIImage loading later on down the road. The inverse (with NSMutableData) is also true, that a file is able to be written to as if it's directly in RAM. As a technique, it could be useful.