Question

In an ARC project, I’m setting a __weak ivar (declared as id __weak weakLayer;) to a CALayer which is retained by it’s superlayer. Most times this works. Sometimes, the weak ivar tests as nil. I wrote some test code to simplify debugging that demonstrates the problem. I expect this to be an infinite loop but it breaks out, usually in less than 20 iterations. The number of iterations required to break out is not consistent.

array = [NSMutableArray array];
while (1) {
  CALayer *layer = [CALayer layer];
  [array addObject:layer];
  weakLayer = layer;
  if (!weakLayer) {
    NSLog (@"nil");
    break;
  }
  NSLog(@"not nil");
}

If I drop a breakpoint with an action of po weakLayer inside the if, it prints a valid object. I have tested on Xcode 4.3.3 and 4.4 with the Lion and Mountain Lion SDKs.

Answer 1

3 people (including myself) have now confirmed this to work on 10.8, but not on 10.7.4.