CODEWITHSUNDEEP
objective-ccore-graphics
Sean256
Sean256

Reputation: 3099

CoreGraphics random crash

This is a little test program to duplicate an intermittent issue in a larger class. The real class creates 4 thumbs of various sizes.

This main.m program will crash 1 out of 5 times it's run with EXC_BAD_ACCESS and highlights CGImageRelease(imgRef); If i comment out CGImageRelease(imgRef) then the app experiences serious memory leaks but doesn't crash...

#import <Foundation/Foundation.h>
#import <Cocoa/Cocoa.h>

int main(int argc, const char * argv[])
{

    @autoreleasepool {


        NSString * image = @"/Users/xxx/Pictures/wallpaper/7gjMT.jpg";
        NSData * imageData = [NSData dataWithContentsOfFile:image];

        CFDataRef imgData = (__bridge CFDataRef)imageData;
        CGImageRef imgRef;
        CGDataProviderRef imgDataProvider = NULL;
        imgDataProvider = CGDataProviderCreateWithCFData(imgData);
        imgRef = CGImageCreateWithJPEGDataProvider(imgDataProvider, NULL, true, kCGRenderingIntentDefault);
        CGDataProviderRelease(imgDataProvider);

        for (int i = 0; i < 1000; i++) {
            // create context, keeping original image properties
            CGColorSpaceRef colorspace = CGImageGetColorSpace(imgRef);

            CGContextRef context = CGBitmapContextCreate(NULL, 2560, 1440,
                                            CGImageGetBitsPerComponent(imgRef),
                                            CGImageGetBytesPerRow(imgRef),
                                            colorspace,
                                            kCGImageAlphaPremultipliedFirst);

            CGColorSpaceRelease(colorspace);

            // draw image to context (resizing it)
            CGContextDrawImage(context, CGRectMake(0, 0, 2560, 1440), imgRef);

            // extract resulting image from context
            CGImageRef newImgRef;
            newImgRef = CGBitmapContextCreateImage(context);
            CGImageRelease(imgRef);
            CGContextRelease(context);

            imgRef = newImgRef;
        }



    }
    return 0;
}

I found if I release the context first then 1 out of 10 failures it highlights CGImageGetBytesPerRow(imgRef) with the same error.

I added a breakpoint for malloc_error_break and got this on CGImageRelease:

enter image description here

Are CGImageRelease and CGImageRelease releasing a shared resource?

Upvotes: 2

Views: 212

Answers (1)

Ken Thomases
Ken Thomases

Reputation: 90681

The main problem is almost certainly that you're releasing a colorspace that you don't own. CGImageGetColorSpace(imgRef) does not give you an ownership of the returned colorspace object, so you shouldn't be calling CGColorSpaceRelease(colorspace) later. (By the way, although I happened to get a different failure that clued me into the problem, the static analyzer catches this, too.)

As a secondary issue, I was getting failures to create the context because you're using an inappropriate bytes-per-row value. CGImageGetBytesPerRow(imgRef) is the bytes-per-row of that image, but that's only appropriate for the width of that image. Given that you're hard-coding a width rather than using the width of the image (since you're scaling), you should not be using the bytes-per-row of the image.

I guess it will work if you're scaling down, but it will waste space. If you're scaling up, it fails.

In any case, pass 0. That lets CGBitmapContextCreate() compute an optimal value.

Upvotes: 2

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