ios - CGDataProviderCopyData 在内存中累积导致崩溃

Question

好吧，我正在从服务器分段下载一堆大图像 (5mb)，然后将这些分段拼接在一起并从字节数组渲染整个图像。但是，我意识到每个图像的数据都没有被释放，因此累积导致内存警告和我的应用程序崩溃。我认为由于我的显式 (__bridge_transfer NSData *) 转换，ARC 会负责释放对象，但它仍然被证明是一个问题。在仪器中，被称为“CGDataProviderCopyData”的约 1mb 的对象会建立起来，并且不会被拼接到整个图像中的每个文件丢弃。任何想法或任何人都可以引导我朝着正确的方向前进？非常感谢。

 // Create  array to add all files into total image
NSMutableArray *byteArray = [[NSMutableArray alloc] initWithCapacity:(imageHeight * imageWidth)];

// Iterate through each file in files array
for (NSString *file in array)
{        
    // Set baseURL for individual file path
    NSString *baseURL = [NSString stringWithFormat:@"http://xx.225.xxx.xxx%@",[imageInfo objectForKey:@"BaseURL"]];

    // Specify imagePath by appending baseURL to file name
    NSString *imagePath = [NSString stringWithFormat:@"%@%@", baseURL, file];

    // Change NSString --> NSURL --> NSData
    NSURL *imageUrl = [NSURL URLWithString:imagePath];
    NSData *imageData = [NSData dataWithContentsOfURL:imageUrl];

    // Create image from imageData
    UIImage *image = [UIImage imageWithData:imageData];
    CGImageRef cgimage = image.CGImage;

    size_t width  = CGImageGetWidth(cgimage);
    size_t height = CGImageGetHeight(cgimage);

    size_t bpr = CGImageGetBytesPerRow(cgimage);
    size_t bpp = CGImageGetBitsPerPixel(cgimage);
    size_t bpc = CGImageGetBitsPerComponent(cgimage);
    size_t bytes_per_pixel = bpp / bpc;

    // Get CGDataProviderRef from cgimage
    CGDataProviderRef provider = CGImageGetDataProvider(cgimage);

    // This is the object that is not being released
    NSData *data = (__bridge_transfer NSData *)CGDataProviderCopyData(provider);      //Using (__bridge_transfer NSData *) casts the provider to type NSData and gives ownership to ARC, but still not discarded

    const UInt8 *bytes = (Byte *)[data bytes];

    // Log which file is currently being iterated through 
    NSLog(@"---Stitching png file to total image: %@", file);

    // Populate byte array with channel data from each pixel
    for(size_t row = 0; row < height; row++)
    {
        for(size_t col = 0; col < width; col++)
        {
            const UInt8* pixel =
            &bytes[row * bpr + col * bytes_per_pixel];

            for(unsigned short i = 0; i < 4; i+=4)
            {
                __unused unsigned short red = pixel[i];         // red channel - unused
                unsigned short green = pixel[i+1];              // green channel
                unsigned short blue = pixel[i+2];               // blue channel
                __unused unsigned short alpha = pixel[i+3];     // alpha channel - unused

                // Create dicom intensity value from intensity = [(g *250) + b]
                unsigned short dicomInt = ((green * 256) + blue);

                //Convert unsigned short intensity value to NSNumber so can store in array as object
                NSNumber *DICOMvalue = [NSNumber numberWithInt:dicomInt];

                // Add to image array (total image)
                [byteArray addObject:DICOMvalue];
            }
        }
    }
    data = nil;
}
return byteArray;

通过 Xcode 运行“分析”也没有显示任何明显的泄漏。

Answer 1

我几乎逐字逐句地获取了这段代码，并做了一些更多的调查。通过 CFDataRef/NSData，我能够看到您在 NSDatas 中遇到的问题并没有消失，并且我能够通过将使用 NSData 的代码部分包装在 @autoreleasepool 中来解决它。范围，如下所示:

 // Create  array to add all files into total image
NSMutableArray *byteArray = [[NSMutableArray alloc] initWithCapacity:(imageHeight * imageWidth)];

// Iterate through each file in files array
for (NSString *file in array)
{        
    // Set baseURL for individual file path
    NSString *baseURL = [NSString stringWithFormat:@"http://xx.225.xxx.xxx%@",[imageInfo objectForKey:@"BaseURL"]];

    // Specify imagePath by appending baseURL to file name
    NSString *imagePath = [NSString stringWithFormat:@"%@%@", baseURL, file];

    // Change NSString --> NSURL --> NSData
    NSURL *imageUrl = [NSURL URLWithString:imagePath];
    NSData *imageData = [NSData dataWithContentsOfURL:imageUrl];

    // Create image from imageData
    UIImage *image = [UIImage imageWithData:imageData];
    CGImageRef cgimage = image.CGImage;

    size_t width  = CGImageGetWidth(cgimage);
    size_t height = CGImageGetHeight(cgimage);

    size_t bpr = CGImageGetBytesPerRow(cgimage);
    size_t bpp = CGImageGetBitsPerPixel(cgimage);
    size_t bpc = CGImageGetBitsPerComponent(cgimage);
    size_t bytes_per_pixel = bpp / bpc;

    // Get CGDataProviderRef from cgimage
    CGDataProviderRef provider = CGImageGetDataProvider(cgimage);

    @autoreleasepool
    {
        // This is the object that is not being released
        NSData *data = (__bridge_transfer NSData *)CGDataProviderCopyData(provider);      //Using (__bridge_transfer NSData *) casts the provider to type NSData and gives ownership to ARC, but still not discarded

        const UInt8 *bytes = (Byte *)[data bytes];

        // Log which file is currently being iterated through 
        NSLog(@"---Stitching png file to total image: %@", file);

        // Populate byte array with channel data from each pixel
        for(size_t row = 0; row < height; row++)
        {
            for(size_t col = 0; col < width; col++)
            {
                const UInt8* pixel =
                &bytes[row * bpr + col * bytes_per_pixel];

                for(unsigned short i = 0; i < 4; i+=4)
                {
                    __unused unsigned short red = pixel[i];         // red channel - unused
                    unsigned short green = pixel[i+1];              // green channel
                    unsigned short blue = pixel[i+2];               // blue channel
                    __unused unsigned short alpha = pixel[i+3];     // alpha channel - unused

                    // Create dicom intensity value from intensity = [(g *250) + b]
                    unsigned short dicomInt = ((green * 256) + blue);

                    //Convert unsigned short intensity value to NSNumber so can store in array as object
                    NSNumber *DICOMvalue = [NSNumber numberWithInt:dicomInt];

                    // Add to image array (total image)
                    [byteArray addObject:DICOMvalue];
                }
            }
        }
        data = nil;
    }
}
return byteArray;

添加 @autoreleasepool 后，然后我注释掉了创建 NSNumbers 并将它们放入数组的部分，并且我能够在 Instruments 的 Allocations 模板中看到，确实 CFData 对象现在在每一轮中都被释放循环。

我注释掉创建 NSNumbers 并将它们放入数组的部分的原因是，使用该代码，您最终将添加 width * height * 4 NS 编号为 byteArray .这意味着即使 NSData 被正确释放，您的堆使用量也会增加 width * height * 4 * <at least 4 bytes, maybe more>无论。也许这就是您需要做的，但这确实让我更难了解 NSData 发生了什么，因为它们的大小与 NSNumber 数组相比显得相形见绌。

希望对您有所帮助。