M P M P - 3 months ago 16x
Objective-C Question

NSImage drawInRect and NSView cacheDisplayInRect memory retained

Application that I am working process images. It's like user drops at max 4 images and app layout them based on user's selected template. One image might be added 2-3 times in final view.

Each image in layout is drawn in NSView (drawRect method of NSView using drawInRect method).Now final image (combined image by layouting all images) is created by saving NSView as Image and it all works very well.

Now problem that I am facing is memory is being retained by app once all processing is done. I have used instruments allocation and I don't see memory leaks but I see "Persistent bytes" are increasing continuously with each session of app and one user reported issue in GB's. Please see screenshot.

Instruments memory usage
When I further investigated in Instruments I saw below code snaps of app that is causing memory retentions. All are related to ImageIO and coreImages. See below from instruments:

Instruments code snap

However this seems to be only problem with 10.10 and above system. Tested same version of the app in 10.9.x and memory usage remains with in 60MB. During session execution in app it goes to 200MB but once it's done it comes back to 50-60MB that usual for kind of app.

[_photoImage drawInRect: self.bounds fromRect: NSZeroRect operation: NSCompositeSourceOver fraction: 1.0 respectFlipped: YES hints: nil];
_photoImage = nil;

Above code I am using to draw image in NSView's drawRect method and code shown in image is being used to get NSView as Image.

Update: After my further investigation I found that it's CGImageSourceCreateWithData that is caching the TIFF data of NSImage. More ever I am using below code to crop the image and if i uncomment it memory consumption just works fine.

NSData *imgData = [imageToCrop TIFFRepresentation];
CGImageSourceRef source = CGImageSourceCreateWithData((CFDataRef)imgData, NULL);
CGImageRef maskRef = CGImageSourceCreateImageAtIndex(source, 0, NULL);
CGImageRef imageRef = CGImageCreateWithImageInRect(maskRef, rect);
NSImage *cropped = [[NSImage alloc] initWithCGImage: imageRef size:rect.size];

//CFRelease( options );
imgData = nil;

I have also trying explicitly setting kCGImageSourceShouldCache to false (but it's by default false) but same results.
Please help to solve the memory retention issue.


Finally after lots of debugging it turns out that CGImageSourceCreateWithData is somewhere retaining TIFF data of NSImage. When I changed this line:

CGImageSourceRef source = CGImageSourceCreateWithData((CFDataRef)imgData, NULL);


CGImageSourceRef source = CGImageSourceCreateWithURL((CFURLRef)[NSURL fileURLWithPath:path], NULL);

everything just started working fine and app's memory usage was dropped from 300MB (for 6images) to 50-60MB and it's consistent behaviour now.

Apart from above changes it was still causing memory retention somewhere so to get rid of that, after all processing is done I cleared image of each layer to 'nil' and that works like charm. I was in impression that making parent as 'nil' would release images as well but that was not working.

Anyway if anyone seems issue with drawInRect or cacheDisplayInRect then make sure to clear out the image if not needed later on.

Update 2nd July 2016

I found that kCGImageSourceShouldCache is false by default in 32bit and true for 64bit. I was able to release memory with below code by setting it to false.

const void *keys[] =   { kCFBooleanFalse};
    const void *values[] = { kCGImageSourceShouldCache };
    CFDictionaryRef optionsDictionary = CFDictionaryCreate(NULL, keys, values, 1, NULL, NULL);

    CGImageSourceRef source = CGImageSourceCreateWithData((__bridge CFDataRef)[image TIFFRepresentation], optionsDictionary);

Hope it helps someone.