iOS 8.1 iPad Air 2 - 图像加载内存错误

Question

To try to explain the problem as succinctly as possible.. I have written an app that force-loads a sequence of very large png's into memory using multithreading with Grand Central Dispatch, into a UIImageView animation sequence. Have been testing until recently on the iPad Air 1 (with its 1GB of RAM), whereby I could only get approximately 40 of these 1.7MB images loaded into memory before the app would crash. Fair enough. But now with the iPad Air 2 I was eager to get my hands on the 2GB of RAM which should easily be enough to get my entire sequence of 180 x 1.7MB png images (yes, I know, but just run with me on this) fully into memory, and then some. But to my dismay it only seems to be able to get up to 111 of them into memory before crashing with the following error in the console;

-[_CSIRenditionBlockData _allocateImageBytes] Allocation of image block data with for CoreUI Rendition failed 2014-10-24 20:21:55.592 TestApp[280:19701] CoreUI: Error while decoding CSI/ZIP compressed image block data (rows 1280 rowbytes 10240 format 0)

The 2GB ram should definitely be able to handle the full sequence of images, three times over, surely? What does the above error allude to? Can anyone help? I really want the Air 2 to hit this out of the park and so far, I've stumbled out of the gate..

The forced image-loading code is performed with this method;

+ (UIImage*)imageImmediateLoadWithContentsOfFile:(NSString*)path {

    UIImage* image = [UIImage imageWithContentsOfFile:path];

    CGFloat w = image.size.width;
    CGFloat h = image.size.height;

    CGFloat scale = image.scale;

    if (image.scale > [[UIScreen mainScreen] scale]) {

        scale = 1.0f;

    } else {

        //NSLog(@"SCREEN SCALE LEAVE ALONE\n");
    }

    CGImageRef cgImage = [image CGImage];

    CGContextRef context = CGBitmapContextCreate(NULL, w*scale, h*scale, CGImageGetBitsPerComponent(cgImage), CGImageGetBytesPerRow(cgImage), CGImageGetColorSpace(cgImage), kCGImageAlphaPremultipliedFirst | kCGBitmapByteOrder32Little);

    CGContextDrawImage(context, CGRectMake(0, 0, w*scale, h*scale), cgImage);

    CGImageRef decompressedImageRef = CGBitmapContextCreateImage(context);
    UIImage* forcedImage = [UIImage imageWithCGImage:decompressedImageRef scale:scale orientation:UIImageOrientationUp];

    CGImageRelease(decompressedImageRef);

    CGContextRelease(context);

    return forcedImage;

}

Grand Central Dispatch is used with dispatch_apply in the following function;

- (void)startImageLoading {

    dispatch_group_async(hardloadGroup, concurrentBackgroundQueue, ^{

        if (abort) return;

        if (targetSlot == 1 || targetSlot == 3) {

            updateLoadingBar = YES;
            loadingProgress = 0.0f;
            loadingIncrement = 1.0f/(float)framecount;

        }

        dispatch_apply(framecount/FLICKBOOK_STRIDE, concurrentBackgroundQueue, ^(size_t i) {

            if (abort) return;

            size_t current = i * FLICKBOOK_STRIDE + 1;
            size_t end = current + FLICKBOOK_STRIDE;

            do {

                if (updateLoadingBar) [self incrementLoadingBar];

                [self hardloadImageForFrame:current++];

            } while (current < end && !abort);

        });

        if (!abort) {

            // MOP-UP ANY LEFTOVER FRAMES AFTER THE STRIDE DIVISION /////////////////////////////////////////////////////////

            for (size_t i = framecount - (framecount % FLICKBOOK_STRIDE) + 1; i <= framecount; i++) {

                if (abort) break;

                if (updateLoadingBar) [self incrementLoadingBar];

                [self hardloadImageForFrame:i];

            }

        }

    });

    // WRITE THE CONTENTS OF THE DICTIONARY TO THE IMAGE ARRAY IN ORDER /////////////////////////////////////////////

    dispatch_group_notify(hardloadGroup, concurrentBackgroundQueue, ^{

        if (!abort) [self performSelectorOnMainThread:@selector(showFlickbook) withObject:nil waitUntilDone:YES];

        [showcaseViewController loadingThreadFinished];

    });

}


- (void)hardloadImageForFrame:(size_t)frame {

    UIImage* forcedImage = [UIImage imageImmediateLoadWithContentsOfFile:[imageNames objectAtIndex:frame-1]];

    @synchronized(self) { [imageArray replaceObjectAtIndex:frame withObject:forcedImage]; }

}

Does anyone know what's causing the problem?

Answer 1

Well, the error is clearly a memory allocation problem. It looks like you are decompressing those 1.7Mb png files into around 12.5Mb each (in the error - 1280 rows each of 10240 bytes). And 111 lots of 12.5Mb is going to use around 1.4Gb. So I think you have hit the maximum you can load, given that iOS and other apps will be using some of that 2Gb.

Not sure why you are "forceLoading these" - presumably it's a performance issue? Do you know whether the time consuming bit comes from reading in the file, or from decompressing the png? If the former, you could try pre-loading the files as NSData objects, and then using UIImage's imageWithData: method or CGImageSourceCreateWithData to build the images on the fly.