Simple CoreGraphics drawing crashes occasionally, but only on iOS 7

Question

I have a piece of code that draws a curve and has been in the app for at least a year without any problems. Over the last three days I am suddenly getting about 10 crash reports per day, all from iOS 7 users. The reports says that the line "for(int i=1 etc" crashes, but I can't begin to understand the problem with that. The crash log refers to CoreGraphics so it is probably the line before that causes the problem. Here is the code:

CGContextBeginPath(cctx);
int step=220/lookupCount;
acx = 0;
acy = hf*100-bestResults[0]*hf*100/top;
CGContextMoveToPoint(cctx, acx, acy);
for(int i=1;i<lookupCount;i++){              //line 2005
    acx = hf*i*step;
    acy = hf*100-bestResults[i]*hf*100/top;
    CGContextAddLineToPoint(cctx, acx , acy);
}
CGContextStrokePath(cctx);

And a piece of the crash log:

Thread 0 Crashed:
0   libsystem_kernel.dylib              0x395311fc ___pthread_kill + 8
1   libsystem_c.dylib                   0x394e202d _abort + 77
2   libsystem_c.dylib                   0x394c1c6b ___assert_rtn + 183
3   CoreGraphics                        0x2ed0da09 CG::Path::is_empty() const + 1
4   racquetTune                         0x000942d5 -[tension autoCorr] (tension.m:2005)

I have been trying to recreate the crash by setting the different variables to zero or make them infinite, but with any "success". Is anyone aware of changes in CoreGraphics in iOS7 that could cause this?

The crashes comes different types of hardware and represent a small number of the users, but are still too frequent to ignore. An interesting detail is that there were no crash reports from the two first days when iOS 7 was available but a steady stream after that.

It turns out that a NaN crashes CGContextAddLineToPoint on iOS7, but not on 5 or 6 (I had only tested an inf number), so this is probably the cause. — Sten, Sep 24 '13 at 05:45
I can reproduce the same crash on iOS7 / iOS8 using [NaN](https://en.wikipedia.org/wiki/NaN#Floating_point) on `CGContextMoveToPoint()` or `CGContextAddLineToPoint()`. To test, use [`NAN`](http://stackoverflow.com/q/16691207/1402846). To workaround, use [`isnan()`](http://stackoverflow.com/q/16691207/1402846). — Pang, Jul 27 '15 at 04:25

score 0 · Answer 1 · answered Oct 13 '13 at 08:47

0

Don't use CGContextMoveToPoint and CGContextAddLineToPoint. Use CGPathMoveToPoint and CGPathAddLineToPoint methods for work with strokePath. In your case :

CGMutablePathRef path= CGPathCreateMutable();
int step=220/lookupCount;
acx = 0;
acy = hf*100-bestResults[0]*hf*100/top;
CGContextMoveToPoint(cctx, acx, acy);
for(int i=1;i<lookupCount;i++){              //line 2005
    acx = hf*i*step;
    acy = hf*100-bestResults[i]*hf*100/top;
    CGContextAddLineToPoint(cctx, acx , acy);
}

    CGContextAddPath(cctx, path);
    CGContextClosePath(cctx);
    CGContextFillPath(cctx);

answered Oct 13 '13 at 08:47

Oleg Sobolev

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For what reason would you avoid `CGContextMoveToPoint` and `CGContextAddLineToPoint`? – Clafou Jul 18 '14 at 15:11
I am interested too why should one avoid CGContextMoveToPoint and CGContextAddLineToPoint ? – sabiland Oct 15 '15 at 11:20

Simple CoreGraphics drawing crashes occasionally, but only on iOS 7

1 Answers1