CIDetector isn't releasing memory - objective-c

Question

I'm using CIDetector as follows multiple times:
-(NSArray *)detect:(UIImage *)inimage
{
UIImage *inputimage = inimage;
UIImageOrientation exifOrientation = inimage.imageOrientation;
NSNumber *orientation = [NSNumber numberWithInt:exifOrientation];
NSDictionary *imageOptions = [NSDictionary dictionaryWithObject:orientation forKey:CIDetectorImageOrientation];
CIImage* ciimage = [CIImage imageWithCGImage:inputimage.CGImage options:imageOptions];
NSDictionary *detectorOptions = [NSDictionary dictionaryWithObject:orientation forKey:CIDetectorImageOrientation];
NSArray* features = [self.detector featuresInImage:ciimage options:detectorOptions];
if (features.count == 0)
{
PXLog(#"no face found");
}
ciimage = nil;
NSMutableArray *returnArray = [NSMutableArray new];
for(CIFaceFeature *feature in features)
{
CGRect rect = feature.bounds;
CGRect r = CGRectMake(rect.origin.x,inputimage.size.height - rect.origin.y - rect.size.height,rect.size.width,rect.size.height);
FaceFeatures * ff = [[FaceFeatures new] initWithLeftEye:CGPointMake(feature.leftEyePosition.x, inputimage.size.height - feature.leftEyePosition.y )
rightEye:CGPointMake(feature.rightEyePosition.x, inputimage.size.height - feature.rightEyePosition.y )
mouth:CGPointMake(feature.mouthPosition.x, inputimage.size.height - feature.mouthPosition.y )];
Face *ob = [[Face new] initFaceInRect:r withFaceFeatures:ff] ;
[returnArray addObject:ob];
}
features = nil;
return returnArray;
}
-(CIContext*) context{
if(!_context){
_context = [CIContext contextWithOptions:nil];
}
return _context;
}
-(CIDetector *)detector
{
if (!_detector)
{
// 1 for high 0 for low
#warning not checking for fast/slow detection operation
NSString *str = #"fast";//[SettingsFunctions retrieveFromUserDefaults:#"face_detection_accuracy"];
if ([str isEqualToString:#"slow"])
{
//DDLogInfo(#"faceDetection: -I- Setting accuracy to high");
_detector = [CIDetector detectorOfType:CIDetectorTypeFace context:nil
options:[NSDictionary dictionaryWithObject:CIDetectorAccuracyHigh forKey:CIDetectorAccuracy]];
} else {
//DDLogInfo(#"faceDetection: -I- Setting accuracy to low");
_detector = [CIDetector detectorOfType:CIDetectorTypeFace context:nil
options:[NSDictionary dictionaryWithObject:CIDetectorAccuracyLow forKey:CIDetectorAccuracy]];
}
}
return _detector;
}
but after having various memory issues and according to Instruments it looks like NSArray* features = [self.detector featuresInImage:ciimage options:detectorOptions]; isn't being released
Is there a memory leak in my code?

Answer 1

I came across the same issue and it seems to be a bug (or maybe by design, for caching purposes) with reusing a CIDetector.
I was able to get around it by not reusing the CIDetector, instead instantiating one as needed and then releasing it (or, in ARC terms, just not keeping a reference around) when the detection is completed. There is some cost to doing this, but if you are doing the detection on a background thread as you said, that cost is probably worth it when compared to unbounded memory growth.
Perhaps a better solution would be, if you a detecting multiple images in a row, to create one detector, use it for all (or maybe, if the growth is too large, release & create a new one every N images. You'll have to experiment to see what N should be).
I've filed a Radar bug about this issue with Apple: http://openradar.appspot.com/radar?id=6645353252126720

Answer 2

I have fixed this problem, you should use #autorelease where you invode the detect method, like this in swift
autoreleasepool(invoking: {
let result = self.detect(image: image)
// do other things
})