在后台线程中读取CGImageRef会使应用程序崩溃 [英] Reading CGImageRef in a background thread crashes the app

问题描述

我有一个很大的jpeg图像，我想在我的opengl引擎中异步加载到图块中. 如果它在主线程上完成，但一切正常，一切都会很好.

i have a big jpeg image that i want to load in tiles asynchronously in my opengl engine. Everything works well if its done on the main thread but its slow.

当我尝试将图块加载到NSOperationBlock上时，尝试访问以前在主线程上加载的共享图像数据指针时，它总是崩溃.

When i try to put the tile loading on an NSOperationBlock, it always crashes when trying to access the shared image data pointer that i previously loaded on the main thread.

必须使用后台操作才能获得某些东西，因为我假设我可以访问我在主线程上创建的内存部分.

There must be something i don't get with background operation because i assume i can access memory sections that i created on the main thread.

我想做的是以下事情:

@interface MyViewer
{
}
@property (atomic, assign) CGImageRef imageRef;
@property (atomic, assign) CGDataProviderRef dataProvider;
@property (atomic, assign) int loadedTextures;
@end

...

- (void) loadAllTiles:(NSData*) imgData
{
    queue = [[NSOperationQueue alloc] init];
    //Loop for Total Number of Textures

    self.dataProvider = CGDataProviderCreateWithData(NULL,[imgData bytes],[imgData length],0);
    self.imageRef = CGImageCreateWithJPEGDataProvider(self.dataProvider, NULL, NO, kCGRenderingIntentDefault);

    for (int i=0; i<tileCount; i++)
    {

       // I also tried this but without luck
       //CGImageRetain(self.imageRef);
       //CGDataProviderRetain(self.dataProvider);

        NSBlockOperation *partsLoading = [[NSBlockOperation alloc] init];
        __weak NSBlockOperation *weakpartsLoadingOp = partsLoading;
        [partsLoading addExecutionBlock: ^ {

            TamTexture2D& pTex2D = viewer->getTile(i);

            CGImageRef subImgRef = CGImageCreateWithImageInRect(self.imageRef, CGRectMake(pTex2D.left, pTex2D.top, pTex2D.width, pTex2D.height));

            //!!!Its crashing here!!!
            CFDataRef cgSubImgDataRef = CGDataProviderCopyData(CGImageGetDataProvider(subImgRef));
            CGImageRelease(subImgRef);

            ...
            }];

        //Adding Parts loading on low priority thread. Is it all right ????
        [partsLoading setThreadPriority:0.0];
        [queue addOperation:partsLoading];

}

推荐答案

我终于发现了我的问题...

I finally found out my problem...

我已经阅读了Quartz2D文档，看来我们不应该再使用CGDataProviderCreateWithData和CGImageCreateWithJPEGDataProvider了.我猜那里的用法不是线程安全的.

I have read the Quartz2D doc and it seems that we should not use CGDataProviderCreateWithData and CGImageCreateWithJPEGDataProvider anymore. I guess there usage is not thread safe.

正如文档所建议的，我现在使用CGImageSource API:

As suggested by the doc, i now use CGImageSource API like this :

self.imageSrcRef = CGImageSourceCreateWithData((__bridge CFDataRef)imgData, NULL);

// get imagePropertiesDictionary
CFDictionaryRef imagePropertiesDictionary = CGImageSourceCopyPropertiesAtIndex(m_imageSrcRef,0, NULL);

self.imageRef = CGImageSourceCreateImageAtIndex(m_imageSrcRef, 0, imagePropertiesDictionary);

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