Memory Leak with ARC

Question

+(void)setup {
    UIImage* spriteSheet = [UIImage imageNamed:@"mySpriteSheet.png"];
    CGRect rect;
    animation = [NSMutableArray arrayWithCapacity:numberOfFramesInSpriteSheet];
    int frameCount = 0;

    for (int row = 0; row < numberFrameRowsInSpriteSheet; row++) {
        for (int col = 0; col < numberFrameColsInSpriteSheet; col++) {
            frameCount++;
            if (frameCount <= numberOfFramesInSpriteSheet) {
                rect = CGRectMake(col*frameHeight, row*frameWidth, frameHeight, frameWidth);
                [animation addObject:[UIImage imageWithCGImage:CGImageCreateWithImageInRect(spriteSheet.CGImage, rect)] ];
            }
         }
    }
}

Compiled the above code with ARC enabled. The Analyze tool reports a possible memory leak since imageWithCGImage:: returns UIImage with count +1, then reference is lost. Leaks Instrument reports no memory leaks at all. Whats going on here?

Furthermore, since ARC prohibits use of manually using release ect, how does one fix the leak?

Thanks to anyone who can offer any advice.

CodaFi · Accepted Answer · 2013-05-27T00:18:25.037

8

ARC does not manage C-types, of which CGImage may be considered. You must release the ref manually when you are finished with CGImageRelease(image);

+(void)setup {
    UIImage* spriteSheet = [UIImage imageNamed:@"mySpriteSheet.png"];
    CGRect rect;
    animation = [NSMutableArray arrayWithCapacity:numberOfFramesInSpriteSheet];
    int frameCount = 0;

    for (int row = 0; row < numberFrameRowsInSpriteSheet; row++) {
        for (int col = 0; col < numberFrameColsInSpriteSheet; col++) {
            frameCount++;
            if (frameCount <= numberOfFramesInSpriteSheet) {
                rect = CGRectMake(col*frameHeight, row*frameWidth, frameHeight, frameWidth);
                //store our image ref so we can release it later
                //The create rule says that any C-interface method with "create" in it's name 
                //returns a +1 foundation object, which we must release manually.
                CGImageRef image = CGImageCreateWithImageInRect(spriteSheet.CGImage, rect)
                //Create a UIImage from our ref.  It is now owned by UIImage, so we may discard it.
                [animation addObject:[UIImage imageWithCGImage:image]];
                //Discard the ref.  
                CGImageRelease(image);
            }
         }
    }
}

edited May 27 '13 at 00:18

answered Sep 22 '12 at 02:00

CodaFi

43,043
8
107
153

2

Also see the accepted answer to my question here: http://stackoverflow.com/questions/6260256/what-kind-of-leaks-does-automatic-reference-counting-in-objective-c-not-prevent/6388601#6388601 – BoltClock Sep 22 '12 at 02:05
"The create rule says that any C-interface method with "create" in it's name returns a +1 foundation object, which we must release manually." - doh! Of course. Thanks CodaFi! Appreciated! – Z.O. Sep 22 '12 at 02:11
@Z.O. No problem. The create rule is actually a little hard to find in the docs, but it's very important when dealing with Apple's C-Interfaces. [Here it is](https://developer.apple.com/library/mac/documentation/CoreFOundation/Conceptual/CFMemoryMgmt/Concepts/Ownership.html#//apple_ref/doc/uid/20001148-103029) (along with the get rule). – CodaFi Sep 22 '12 at 02:17
@nielsbot If we're getting technical, then CG- prefixed structures aren't a part of Core Foundation, so I called them foundation types in line with what the documentation calls them. They follow the exact same rules though, so the terms are interchangeable. – CodaFi Sep 22 '12 at 14:24
If the docs call them foundation types I guess we should use that. Too bad we also have Foundation, however. – nielsbot Sep 22 '12 at 16:23

score 3 · Answer 2 · answered Sep 22 '12 at 06:23

3

None of the core foundation data structure is dealt with ARC. Many a times this creates a problem. In these case we have to manually release the memory.

answered Sep 22 '12 at 06:23

Anoop Vaidya

46,283
15
111
140

Memory Leak with ARC

2 Answers2

Linked