xcode incomprehensible exception

Question

I am writing ios app which receives frames from ip camera and show them with UIImage and timer. But from time to time I encounter a incomprehensible exception.
Here is a stack

thread #1: tid = 0x72198, 0x0553a240 vImage`vConvert_RGB888toBGRA8888 + 1760, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=1, address=0xe429000)

frame #0: 0x0553a240 vImage`vConvert_RGB888toBGRA8888 + 1760  
frame #1: 0x05523280 vImage`vImageConvert_RGB888toBGRA8888 + 96
frame #2: 0x01f2f1aa CoreGraphics`CGSConvertBGR888toRGBA8888 + 165  
frame #3: 0x01f5a83e CoreGraphics`argb32_image + 4830
frame #4: 0x0ae007ad libRIP.A.dylib`ripl_Mark + 38  
frame #5: 0x0ae101e1 libRIP.A.dylib`RIPLayerBltImage + 1187
frame #6: 0x0adfcc59 libRIP.A.dylib`ripc_RenderImage + 258  
frame #7: 0x0adfb0cb libRIP.A.dylib`ripc_DrawImage + 1051
frame #8: 0x01fe4865 CoreGraphics`CGContextDrawImage + 435  
frame #9: 0x01657498 QuartzCore`CA::Render::(anonymous namespace)::create_image_by_rendering(CGImage*, CGColorSpace*, unsigned int) + 708
frame #10: 0x01656f31 QuartzCore`CA::Render::create_image(CGImage*, CGColorSpace*, unsigned int) + 2261  
frame #11: 0x0165784d QuartzCore`CA::Render::copy_image(CGImage*, CGColorSpace*, unsigned int, double) + 430
frame #12: 0x01738d10 QuartzCore`-[CALayer(CALayerPrivate) _copyRenderLayer:layerFlags:commitFlags:] + 557  
frame #13: 0x0173a031 QuartzCore`CA::Layer::copy_render_layer(CA::Transaction*, unsigned int, unsigned int*) + 57
frame #14: 0x0168fc9d QuartzCore`CA::Context::commit_layer(CA::Layer*, unsigned int, unsigned int, void*) + 119  
frame #15: 0x0172a727 QuartzCore`CA::Layer::commit_if_needed(CA::Transaction*, void (*)(CA::Layer*, unsigned int, unsigned int, void*), void*) + 317
frame #16: 0x0172a6a7 QuartzCore`CA::Layer::commit_if_needed(CA::Transaction*, void (*)(CA::Layer*, unsigned int, unsigned int, void*), void*) + 189  
frame #17: 0x0172a6a7 QuartzCore`CA::Layer::commit_if_needed(CA::Transaction*, void (*)(CA::Layer*, unsigned int, unsigned int, void*), void*) + 189
frame #18: 0x01690dd6 QuartzCore`CA::Context::commit_transaction(CA::Transaction*) + 1794  
frame #19: 0x01691b85 QuartzCore`CA::Transaction::commit() + 393
frame #20: 0x0174f5b0 QuartzCore`+[CATransaction flush] + 52  
frame #21: 0x021909b6 UIKit`_UIWindowUpdateVisibleContextOrder + 232
frame #22: 0x02190825 UIKit`+[UIWindow _prepareWindowsPassingTestForAppResume:] + 28  
frame #23: 0x02190a0f UIKit`+[UIWindow _prepareWindowsForAppResume] + 41
frame #24: 0x02164972 UIKit`-[UIApplication _handleApplicationResumeEvent:] + 80  
frame #25: 0x0216593f UIKit`-[UIApplication handleEvent:withNewEvent:] + 1898
frame #26: 0x02166555 UIKit`-[UIApplication sendEvent:] + 85  
frame #27: 0x02153250 UIKit`_UIApplicationHandleEvent + 683
frame #28: 0x04c6bf02 GraphicsServices`_PurpleEventCallback + 776  
frame #29: 0x04c6ba0d GraphicsServices`PurpleEventCallback + 46
frame #30: 0x0368eca5 CoreFoundation`__CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ + 53  
frame #31: 0x0368e9db CoreFoundation`__CFRunLoopDoSource1 + 523
frame #32: 0x036b968c CoreFoundation`__CFRunLoopRun + 2156  
frame #33: 0x036b89d3 CoreFoundation`CFRunLoopRunSpecific + 467
frame #34: 0x036b87eb CoreFoundation`CFRunLoopRunInMode + 123  
frame #35: 0x04c6a5ee GraphicsServices`GSEventRunModal + 192
frame #36: 0x04c6a42b GraphicsServices`GSEventRun + 104  
frame #37: 0x02152f9b UIKit`UIApplicationMain + 1225
frame #38: 0x00009344 thin_client_v2`main(argc=1, argv=0xbfffee4c) + 164 at main.m:17

But I think It is not really helpful so how can I understand which line of my code raises exception? I added All Exceptions breakpoint and this tricks but it did not help me.

Thanks

PS
So I added zombie objects to my project. As I understand it will help me to get more correct stack trace.
About creating image. Here is my code

- (UIImage *)imageFromAVPicture:(AVPicture)pict width:(int)width height:(int)height    
{
    CGBitmapInfo bitmapInfo = kCGBitmapByteOrderDefault;
    CFDataRef data = CFDataCreateWithBytesNoCopy(kCFAllocatorDefault, pict.data[0], pict.linesize[0]*height,kCFAllocatorNull);
    CGDataProviderRef provider = CGDataProviderCreateWithCFData(data);
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    CGImageRef cgImage = CGImageCreate(width, 
                                       height, 
                                       8, 
                                       24, 
                                       pict.linesize[0], 
                                       colorSpace, 
                                       bitmapInfo, 
                                       provider, 
                                       NULL, 
                                       NO, 
                                       kCGRenderingIntentDefault);
    CGColorSpaceRelease(colorSpace);
    UIImage *image = [UIImage imageWithCGImage:cgImage];

    CGImageRelease(cgImage);
    CGDataProviderRelease(provider);
    CFRelease(data);

    return image;
}

But I think that if the problem was in this method it would have crashed all the time, right? But exception happens really rare.

EXC_BAD_ACCESS is a Mach exception, not an Objective-C exception. See http://stackoverflow.com/questions/327082/exc-bad-access-signal-received — tsnorri, Aug 08 '14 at 12:41
In addition to what Ian Ollmann wrote, you are passing `kCFAllocatorDefault` to `CFDataCreateWithBytesNoCopy`. As a result, when your `data` object gets deallocated, it will try to use the default allocator to free the memory at `pict.data[0]`. This probably isn't what you want. — tsnorri, Aug 08 '14 at 19:58
I think I would use CGDataProviderCreateWithData() to create the data provider, and retain the AVPicture. In the release callback, I would release the AVPicture. (This assumes that AVPicture is reference counted.) — Ian Ollmann, Aug 08 '14 at 20:17
Looks like it's from FFmpeg. https://www.ffmpeg.org/doxygen/trunk/structAVPicture.html — tsnorri, Aug 08 '14 at 21:32
Oh well. Whatever owns the AVPicture will have to defer deleting it until after that callback fires. — Ian Ollmann, Aug 08 '14 at 23:28

score 2 · Accepted Answer · answered Aug 08 '14 at 16:04

It means your app is crashing because it touched unmapped memory.

This commonly can happen if you create a CGImageRef using a CGDataProviderRef which was initialized with no copy, and then release the pixels before the CGImageRef dies. This leaves a CGImageRef pointing to garbage, which will crash if you try to draw it. If you are pretty sure that you aren't doing that and you can come up with a reproducible sample case, then I recommend filing a bug with Apple: http://bugreporter.apple.com

xcode incomprehensible exception

1 Answers1