memory growth when using blocks & Path's FastImageCache

Question

I am using Path's excellent FastImageCache library and am running into a retain problem.

Specifically, when trying to provide UIImages (downloaded from a server) to the image cache. The images, when handed to the completion block, seems to remain retained. ARC is not releasing is.

When dealing with a very large number of large images, this leads to a dramatic memory growth.

- (void)imageCache:(FICImageCache *)imageCache wantsSourceImageForEntity:(id<FICEntity>)entity withFormatName:(NSString*)formatName completionBlock:(FICImageRequestCompletionBlock)completionBlock
{
    ...
    NSData * data = [NSURLConnection sendSynchronousRequest:urlRequest
                                              returningResponse:&response
                                                          error:&error];
    UIImage* image = [[UIImage alloc] initWithData:data];
    completionBlock(image); // <-----
    ...
}

I verified that not calling the completion block with the image, does not lead to the memory growth.

Also, not using the image in the drawing block itself, also avoids the memory growth. So i assume this is indeed related to the image being retained.

- (FICEntityImageDrawingBlock)drawingBlockForImage:(UIImage*)image withFormatName:(NSString*)formatName
{
    FICEntityImageDrawingBlock drawingBlock = ^(CGContextRef contextRef, CGSize contextSize) {
        CGRect contextBounds = CGRectZero;
        contextBounds.size = contextSize;
        CGContextClearRect(contextRef, contextBounds);
        CGContextSetInterpolationQuality(contextRef, kCGInterpolationMedium);
        UIGraphicsPushContext(contextRef);
        [image drawInRect:contextBounds]; // <---- 
        UIGraphicsPopContext();
    };

    return drawingBlock;
}

How can i avoid the image being retained or how can i force it to be released? I tried setting it to nil and adding a @autoreleasepool but that didn't help.

@autoreleasepool {
        NSData * data = [NSURLConnection sendSynchronousRequest:urlRequest
                                              returningResponse:&response
                                                          error:&error];

        UIImage* image = [[UIImage alloc] initWithData:data];
        completionBlock(image);
        image = nil;
        data = nil;

        [[NSURLCache sharedURLCache] removeAllCachedResponses];
    }

Thanks for the help.

UPDATE 3/18/2014
Note: this does NOT appear to be an issue in the simulator, only on the device.

Try using an "autoreleased" `UIImage` class method instead of alloc/init. — Ryan Romanchuk, Nov 10 '14 at 16:40

score 0 · Answer 1 · answered Mar 17 '14 at 22:04

0

I'm not sure it's your image that's leaking - I think it may be the context passed into your drawing block. Can you assert that you are freeing it, after it's done being used?

answered Mar 17 '14 at 22:04

greymouser

3,133
19
22

yes, the context is being released by Path's image cache like such: `CGContextRelease(context);` – Reneli Mar 17 '14 at 23:20

Ryan Romanchuk · Answer 2 · 2014-11-10T16:39:28.473

So I started leaking here as well, most likely from some subtle retain cycle, but for whatever reason when I switched to imageWithContentsOfFile from initWithData my problem went away. I haven't spent time investigating why, but I'm sure there are implications using [[UIImage alloc] initWithData:data]; that's preventing this uiimage from getting released. I suppose this makes sense, especially if you're doing this inside a block, the allocation probably caused our reference count to go +1 followed by the blocks strong reference creating the cycle limbo.

After making this change, I checked back with Instruments and my heap was no longer ballooning. It was very easy for me to find this because I also have very large images so my living mem usage would immediately skyrocket and crash soon after.

score 0 · Answer 3 · answered Nov 14 '14 at 13:50

thanks for comment of @Ryan Romanchuk. I tried the method you mentioned(change from initWithData to imageWithContentsOfFile). And I check the code of author, find he also used imageWithContentsOfFile(mine is imageWithCGImage) . It works for me. This is what I did: save the photos as jpeg file, load image using imageWithContentsOfFile. Finally, the memory allocation went down dramatically. However, I still can observe slight allocation growth. Look at my screenshot:

1) I made several generations to observe ram growth. There are some growth about 1M. enter image description here

2) I dig one generation deeper, and find the growth is related with saveMetadata. enter image description here

3) located at NSDictionary *metadataDictionary = [NSDictionary dictionaryWithObjectsAndKeys: [_indexMap copy], FICImageTableIndexMapKey, [_sourceImageMap copy], FICImageTableContextMapKey, [[_MRUEntries array] copy], FICImageTableMRUArrayKey, [_imageFormatDictionary copy], FICImageTableFormatKey, nil]; enter image description here

memory growth when using blocks & Path's FastImageCache

3 Answers3