UIGraphicsGetImageFromCurrentImageContext memory leak with previews

Question

I\'m trying to create previews images of pages in a PDF but I have some problems with the release of memory.

I wrote a simple test algorithm that cycles on the probl

Answer 1

I know it's an old question, but I've just been banging my head against the wall on this for a few hours. In my app repeatedly calling

UIImage *image = UIGraphicsGetImageFromCurrentImageContext()

in a loop does hold on to the memory despite me calling image = nil; Not sure how long the app would keep hold of the memory before freeing, but it's certainly long enough for my app to get a memory warning then crash.

I managed to solve it finally by wrapping the code that calls / uses the image from UIGraphicsGetImageFromCurrentImageContext() in @autoreleasepool. So I have:

@autoreleasepool {
    UIImage *image = [self imageWithView:_outputImageView]; //create the image
    [movie addImage:image frameNum:i fps:kFramesPerSec];    //use the image as a frame in movie
    image = nil;
}

Hope that might help someone.

Answer 2

The problem is this:

UIGraphicsGetImageFromCurrentImageContext()

returns an autoreleased UIImage. The autorelease pool holds on to this image until your code returns control to the runloop, which you do not do for a long time. To solve this problem, you would have to create and drain a fresh autorelease pool on every iteration (or every few iterations) of your while loop.

Answer 3

I've had the same problem working with big images. Adding a padding to an image or applying a filter resulted with 200MB of memory allocation without releasing it while the image was on the screen.

Found a working way to fix this problem:

extension UIImage {
  func release() -> UIImage? {
    guard let data = UIImageJPEGRepresentation(self, 1.0) else { return nil }
    return UIImage(data: data)
  }
}

Also tried it with UIImagePNGRepresentation but it seems to not release the allocation neither.

Answer 4

For future reference here's what I did to solve this (tested in Swift 4).

I was calling the function below for every new image downloaded from the internet (on a utility queue). Before implementing the autorelease pool it would crash after processing about 100.

For simplicity, in the resizeImage function I've removed needed code except for the autoreleasepool and the part that was leaking.

private func resizeImage(image: UIImage, toHeight: CGFloat) -> UIImage {
    return autoreleasepool { () -> UIImage in
        [...]

        let newImage = UIGraphicsGetImageFromCurrentImageContext() //Leaked
        UIGraphicsEndImageContext()

        return newImage!
    }

}

I hope this helps!

Answer 5

your line of crash you can update it like following

get one UIimage out of loop

rendered_image = UIGraphicsGetImageFromCurrentImageContext();

Answer 6

For those who tried all solution above and still has a memory leak, check if you are using a dispatch queue. If so, be sure to set its autoreleaseFrequency to .workItem. Or the autorelease pool you set up inside the will not execute.

DispatchQueue(label: "imageQueue", qos: .userInitiated, autoreleaseFrequency: .workItem)

Hope it helps, it has bugged me for hours until I finally realize that's DispatchQueue that is holding the block.