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ios - ARC中的这种dealloc有什么问题？

我正在开发一个进行图像处理并显示结果图像的应用程序。我使用UIScrollView允许用户滚动所有图像，因为该图像不是标准的jpg或png，因此加载需要花费时间。我使用GCD异步加载，当完成分配到主队列的显示时。摘录如下:

- (void)loadImage:(NSString *)name
{
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        UIImage *image = [Reader loadImage:name];
        dispatch_sync(dispatch_get_main_queue(), ^{
            [self displayImage:image];
        });
    });
}

Reader的loadImage方法如下:
+ (UIImage *)loadImage:(NSString *)name
{
   UInt8 *data = NULL;
   NSString *mfjPath = [TMP stringByAppendingPathComponent:name];
   NSData *mfjData = [NSData dataWithContentsOfFile:mfjPath];
   if(mfjData){
        data = malloc(sizeof(UInt8)*mfjData.length);
        [mfjData getBytes:data];
   }
   if(data){
        ResultHolder *result = [sDecoder decodeData:data withOffset:0];// static id<IDecoder> sDecoder; in Reader.m before @implementation Reader.
        return [result bitmap];
   }
    retun nil;
}
IDCoder是一个协议
@protocol IDecoder <NSObject>
- (ResultHolder *)decodeData:(UInt8 *) withOffset:(int)offset;
@end
ResultHolder是用于加载简单图像并组合复杂图像的类。如下:

结果保持器
typedef struct color24{
    UInt8 R;
    UInt8 G;
    UInt8 B;
} Color24;

@interface ResultHolder : NSObject
{
    unsigned long mWidth;
    unsigned long mHeight;
    UInt8 *mData;
    CGImageRef mBitmap;

    BOOL isMonoColor;
    Color24 mMonoColor;
}

+ (ResultHolder *)resultHolderWithCGImage:(CGImageRef)image;
+ (ResultHolder *)resultHolderWithData:(UInt8 *)data Width:(unsigned long)width andHeight:(unsigned long)height;
+ (ResultHolder *)resultHolderWithMonoColor:(Color24)monoColor withWidth:(unsigned long)width andHeight:(unsigned long)height;

- (ResultHolder *)initWithData:(UInt8 *)data Width:(unsigned long)width andHeight:(unsigned long) height;
- (ResultHolder *)initWithCGImage:(CGImageRef)image;
- (ResultHolder *)initWithMonoColor:(Color24)monoColor withWidth:(unsigned long)width andHeight:(unsigned long)height;

- (BOOL)isSuccess;
- (UIImage *)bitmap;
- (void)combineFixResultHolder:(ResultHolder *)child Rect:(CGRect)bounds Width:(unsigned long)width andHeight:(unsigned long)height;
- (void)combineResultHolder:(ResultHolder *)child Bounds:(CGRect)bounds Width:(unsigned long)width andHeight:(unsigned long)height;
@end

ResultHolder.m
@implementation ResultHolder

@synthesize width = mWidth;
@synthesize height = mHeight;
@synthesize isMonoColor;
@synthesize monoColor = mMonoColor;

- (ResultHolder *)initWithData:(UInt8 *)data Width:(unsigned long)width andHeight:(unsigned long)height
{

    if (self = [super init]) {
        mWidth = width;
        mHeight = height;
        mData = malloc(mWidth*mHeight*sizeof(Color24));
        memcpy(mData, data, mWidth*mHeight*sizeof(Color24));

        mBitmap = NULL;
    }

    return self;
}

- (ResultHolder *)initWithCGImage:(CGImageRef)image
{
    if (self = [super init]) {
        mBitmap = CGImageRetain(image);
        mWidth = CGImageGetWidth(image);
        mHeight = CGImageGetHeight(image);
    }
    return self;
}

- (ResultHolder *)initWithMonoColor:(Color24)monoColor withWidth:(unsigned long)width andHeight:(unsigned long)height
{
    if (self = [super init]) {
        mMonoColor = monoColor;

        isMonoColor = YES;
        mWidth = width;
        mHeight = height;
        mBitmap = NULL;
        mData = NULL;
    }

    return self;
}

+ (ResultHolder *)resultHolderWithCGImage:(CGImageRef)image
{
    ResultHolder *resultHolder = [[ResultHolder alloc] initWithCGImage:image];
    return resultHolder;
}

+ (ResultHolder *)resultHolderWithData:(UInt8 *)data Width:(unsigned long)width andHeight:(unsigned long)height
{
    ResultHolder *resultHolder = [[ResultHolder alloc] initWithData:data Width:width andHeight:height];
    return resultHolder;
}

+ (ResultHolder *)resultHolderWithMonoColor:(Color24)monoColor withWidth:(unsigned long)width andHeight:(unsigned long)height
{
    ResultHolder *resultHolder = [[ResultHolder alloc] initWithMonoColor:monoColor withWidth:width andHeight:height];
    return resultHolder;
}

- (BOOL)isSuccess
{
    if ([ReaderConfigures CodecDebug])
        NSLog(@"ResultHolder isSuccess");
    return (mData != NULL || isMonoColor || mBitmap != nil);
}

- (void)fillMonoColor
{

    if (isMonoColor) {
        if (mData) {
            free(mData);
        }
        mData = (UInt8 *)malloc(mWidth*mHeight*sizeof(Color24));

        for (int i = 0; i < mHeight; i++) {
            for (int j = 0; j < mWidth; j++) {
                memcpy(mData+(i*mWidth+j)*3, &mMonoColor, sizeof(Color24));
            }
        }
        isMonoColor = NO;
    }
}


- (void)extractBitmap
{
    if (mBitmap) {

        CGDataProviderRef dataProvider = CGImageGetDataProvider(mBitmap);
        CFDataRef bitmapData = CGDataProviderCopyData(dataProvider);
        UInt8 * dataSource = (UInt8 *)CFDataGetBytePtr(bitmapData);

        size_t width = CGImageGetWidth(mBitmap);
        size_t height = CGImageGetHeight(mBitmap);
        if(mData)
            free(mData);
        mData = malloc(width*height*3);

        for (int i = 0; i < height; i++) {
            for (int j = 0; j < width; j++) {
                memcpy(mData+(i*width+j)*3, dataSource+(i*width+j)*4, sizeof(Color24));
            }
        }

        CFRelease(bitmapData);
        CGImageRelease(mBitmap);
        mBitmap = NULL;
    }
}


- (UInt8 *)getRawData
{

    if (mBitmap) {
        [self extractBitmap];
    }
    if (isMonoColor) {
        [self fillMonoColor];
    }

    return mData;
}

- (UIImage *)bitmap
{
    if (mBitmap) {
        UIImage *image = [[UIImage alloc] initWithCGImage:mBitmap];
        CGImageRelease(mBitmap);
        mBitmap = NULL;
        return image;
    }
    if (isMonoColor) {
        [self fillMonoColor];
    }
    if (mData) {
        CGDataProviderRef dataProvider = CGDataProviderCreateWithData(NULL, mData, mWidth*mHeight*3, NULL);
        CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
        CGImageRef bitmap = CGImageCreate(mWidth, mHeight, 8, 24, mWidth*3, colorSpace, kCGBitmapByteOrderDefault, dataProvider, NULL, YES, kCGRenderingIntentDefault);
        CGColorSpaceRelease(colorSpace);
        CGDataProviderRelease(dataProvider);
        UIImage *image = [[UIImage alloc] initWithCGImage:bitmap];
        CGImageRelease(bitmap);

        return image;
    }

    return nil;
}

- (void)combineResultHolder:(ResultHolder *) child Bounds:(CGRect) bounds Width:(unsigned long)width andHeight:(unsigned long)height
{
    CGRect rect = CGRectMake(MAX(0, bounds.origin.x), MAX(0, bounds.origin.y),MIN(width - 1, bounds.origin.x + bounds.size.width), MIN(height - 1, bounds.origin.y + bounds.size.height));

    int w = MIN(rect.size.width + 1, child.width);
    int h = MIN(rect.size.height + 1, child.height);

    int dstPos = (height - 1 - (rect.origin.y + h - 1))*width;

    UInt8 *dataParent = [self getRawData];

    if (child.isMonoColor) {
        Color24 childMonoColor = child.monoColor;
        for (int i = 0; i < h; i++) {
            memcpy(dataParent+(dstPos+(int)rect.origin.x)*3, &childMonoColor, w*3);
            dstPos += width;
        }

    } else {
        UInt8 *dataChild = [child getRawData];
        if (dataChild != nil) {
            int srcPos = 0;
            for (int i = 0; i < h; i++) {
                memcpy(dataParent+dstPos*3+((int)rect.origin.x)*3, dataChild+srcPos*3, w*3);
                srcPos += child.width;
                dstPos += width;
            }
        }

    }

}

- (void)combineFixResultHolder:(ResultHolder *)child Rect:(CGRect)bounds Width:(unsigned long)width andHeight:(unsigned long)height
{
    CGRect rect = CGRectMake(bounds.origin.x, height-1-bounds.origin.y-bounds.size.height, bounds.origin.x+bounds.size.width, height-1-bounds.origin.y);

    [self combineResultHolder:child Bounds:rect Width:width andHeight:height];
}

- (void)dealloc
{
    if (mData) {
        free(mData);
        mData = NULL;
    }
    if (mBitmap) {
        CGImageRelease(mBitmap);
        mBitmap = NULL;
    }
}

@end

对于简单图像，例如仅JPEG图像，将调用+ (ResultHolder *)resultHolderWithCGImage:(CGImageRef)image;和- (UIImage *)bitmap;方法。对于一些复杂的ResultHolder将mBitmap提取为mData，然后与sub resultHolder的mData组合以获取图像。如果我在主线程中加载图像，这些方法效果很好，但是如果我使用GCD或NSThread在后台加载图像，则很容易崩溃，尤其是在后台加载复杂的图像时。当应用程序崩溃时，主线程状态为CGSConvertBGR888toRGBA8888方法错误，其他线程之一正在运行[ResultHolder dealloc]方法，实际上是free(mData)。似乎在加载线程和主线程之间存在内存冲突。

当应用崩溃时，错误是这样的:

我已经为这个错误苦苦挣扎了好几天，但仍然找不到解决方法。
我希望有人能帮助我。
任何建议表示赞赏。

更新:
我制作了一个演示项目ReaderDemo来模拟这种情况。如果您有兴趣，可以下载以查看错误。此项目中有15张图像，其中5,7,14张图像在滚动时会导致崩溃，它们比其他图像有些复杂。但是如果您在缩略图滚动视图中滚动然后单击，它们都可以显示。

最佳答案

您有许多问题，但让我们从我发现的第一个问题开始:

  • 测试不当
    if (index > [mPageNames count]) {

    这必须是> =，否则会崩溃。
  • ，您正在mainQueue上调用dispatch_sync，这似乎不是一个好决定(但也许您有一个非常好的决定)-我将其更改为async，似乎可以正常工作
  • 如果在此项目中启用了例外，它将对您有所帮助。单击Xco​​de工具栏中的“断点”按钮。然后在左窗格中选择BreakPoints选项，然后从右窗格中选择第二个。点击左下方的“+”图标并添加一个“所有例外”断点。现在，当您运行调试器时，将在发生问题的地方停止。
  • 我遇到了最后的崩溃，让您修复:
    2012-09-26 08:55:12.378 ReaderDemo[787:11303] MFJAtIndex index out of bounds,index:15,bounds:15
2012-09-26 08:55:12.379 ReaderDemo[787:11303] *** Assertion failure in -[ImageScrollView showLoadingForMFJ:], /Volumes/Data/Users/dhoerl/Downloads/ReaderDemo/ReaderDemo/ImageScrollView.m:247

    • 这应该可以帮助您。

    编辑:您的问题与mData内存的管理有关。您正在尝试在代码中管理它的生命周期，但是此管理未与尝试使用它的CGImageDataProvider同步。崩溃几乎是肯定的(意味着我确信99.99％)是在类释放了dealloc中的内存之后CGImageProvided创建的CGDataProviderCreateWithData试图访问数据的副产品。我在数据提供者上也有类似的经历。

    正确的解决方案是删除所有free(data)调用，或者至少删除其中的大多数。给定代码的当前结构，您将需要仔细考虑-您可能想要用标志替换所有测试和malloc / frees。最后，您要做的是将内存指针从ovdr传递给CGDataProviderCreateWithData之后，您需要将NULL移出mData并让数据提供者处理删除操作。

    这样做的方法是在过去的参数中提供指向CGDataProviderCreateWithData的函数指针:
    CGDataProviderReleaseDataCallback
A callback function that releases data you supply to the function CGDataProviderCreateWithData.

typedef void (*CGDataProviderReleaseDataCallback) (
   void *info,
   const void *data,
   size_t size
);

    该功能所需要做的只是调用free(data);。因此，只要数据提供者完成分配的内存，它就会释放它(您不必担心)。

    关于ios - ARC中的这种dealloc有什么问题？，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/12580801/

    10-14 23:44
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