I’ve been doing some lower level graphics stuff recently for my Photo Booth app and ran into some interesting memory leaks. I had a feeling something was off so ran Instruments after coding, and sure enough, leaks were detected. Several actually. The culprits:

CGPathRef

The biggest offender by far. Forgetting to call CGPathRelease(path) after any form of CGPathCreate…() was the most comment mistake. An interesting case also came up with holding onto an instance variable of the path. So I had this path that was expensive to calculate and gets reused, so I save it into an instance variable:

@property (nonatomic) CGPathRef scaledActivePath;

But when it does get recalculated, I want to release the previous saved path, so I override the setter:

- (void)setScaledActivePath:(CGPathRef)scaledActivePath {
    CGPathRelease(_scaledActivePath);
    
    _scaledActivePath = scaledActivePath;
}

And finally, it needs to be released when the view controller is finished with:

- (void)dealloc {
    CGPathRelease(self.scaledActivePath);
}

 

Image construction with malloc()

In this case, I’m creating a color picker by calculating r, g, b values and placing them into a UInt8 * array, which is then used to create a CGDataProviderRef and CGImageRef. 

The final result looked great:

The code involved looked like:

NSInteger width = self.shadePicker.frame.size.width;
NSInteger height = self.shadePicker.frame.size.height;
NSInteger dataLength = width * height * 4;
self.shadeData = (UInt8 *) malloc(dataLength * sizeof(UInt8));

for (int column = 0; column < width; column++) {
    for (int row = 0; row < height; row++) {
        long i = (column + row * width) * 4;
        
        CGFloat r;
        CGFloat g;
        CGFloat b;
        
        [self colorForBaseHue:hue
                       column:column row:row
                        width:width height:height
                            r:&r g:&g b:&b];
        
        self.shadeData[i] = r;
        self.shadeData[i+1] = g;
        self.shadeData[i+2] = b;
        self.shadeData[i+3] = 255.0;
    }
}

CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
CGDataProviderRef dataProvider = CGDataProviderCreateWithData(NULL, self.shadeData, dataLength, NULL);
CGImageRef imgRef = CGImageCreate(width, height, 8, 32, 4 * width, colorSpace,kCGImageByteOrder32Big | kCGImageAlphaPremultipliedLast, dataProvider, NULL, true, kCGRenderingIntentDefault);
UIImage *img = [UIImage imageWithCGImage:imgRef];

CGImageRelease(imgRef);
CGColorSpaceRelease(colorSpace);
CGDataProviderRelease(dataProvider);

Notice what’s missing?… Read the rest