Bug in UIKit string drawing method?

Question

In order to replicate a crash I was having in my application, I had to create a sample with a slightly exaggerated repeat rate that might not be practical, but one that demo

Answer 1

This appears to be a regression in iOS 5.x: It happens on the 5.0 and 5.1 simulators and on a 5.1 device, but not on the 4.3 simulator or a 4.3.2 device.

It's also specifically the string drawing that seems to be broken — if all you do is string-drawing (avoiding the overhead of creating/destroying contexts), the crash happens nearly instantly:

-(void)threadFunc:(UIFont *)font {
  @autoreleasepool {
    NSString *string = @" ";
    CGRect r = {{0,0},{50,50}};
    UIGraphicsBeginImageContextWithOptions(r.size, YES, 0);
    for(;;) {
      @autoreleasepool {
        [string drawAtPoint:r.origin withFont:font];
      }
    }
    UIGraphicsEndImageContext();
  }
}

-(void)startThreads
{
  UIFont * font = [UIFont systemFontOfSize:12];
  for (int i = 2; i--;)
  {
    [NSThread detachNewThreadSelector:@selector(threadFunc:) toTarget:self withObject:font];
  }
}

EDIT: It is "nearly instant" only in multi-core environments (i.e. a dual-core device or the simulator, assuming a multi-core Mac). Otherwise, it takes on the order of 10-20 minutes to crash. I don't have a dual-core iOS 4.x device (the only possibility appears to be the iPad 2), but the single-core devices haven't crashed after over an hour.

I've raised a bug with Apple, and encourage you to do the same if it affects you.