CIDetector isn't releasing memory

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
            })