iOS app sometimes crashes when dereferencing weak reference - ios

Question

I have a very simple class:
#interface WORef : NSObject
#property(nonatomic,weak) NSObject * object;
#end
Instances are stored in an NSArray and from time to time (only on the main thread) this array is iterated and I access the "object" property.
All works fine when testing or debugging, but in the production version of my app on the store I sometimes get crash reports when dereferencing the "object" property (the stack trace actually shows the line number of the property definition).
Here is an example of such a call stack:
Thread : Crashed: com.apple.main-thread
0 libsystem_platform.dylib 0x35180518 _os_lock_recursive_abort + 18446744073709552000
1 libsystem_platform.dylib 0x3518050f _os_lock_handoff_lock_slow + 90
2 libobjc.A.dylib 0x34adac3f objc_object::sidetable_release_slow((anonymous namespace)::SideTable*, bool) + 22
3 libobjc.A.dylib 0x34adad2f objc_object::sidetable_release(bool) + 118
4 Foundation 0x27f56f01 -[NSOperationQueue dealloc] + 72
5 libobjc.A.dylib 0x34adad5f objc_object::sidetable_release(bool) + 166
6 libobjc.A.dylib 0x34ac14d9 _class_initialize + 536
7 libobjc.A.dylib 0x34ac705f lookUpImpOrForward + 254
8 libobjc.A.dylib 0x34ac6f1b lookUpImpOrNil + 26
9 libobjc.A.dylib 0x34abfab3 class_getMethodImplementation + 34
10 libobjc.A.dylib 0x34ada583 weak_read_no_lock + 58
11 libobjc.A.dylib 0x34ada871 objc_loadWeakRetained + 92
12 MyApp 0x000c5983 -[WORef object] (WeakRef.m:12)
Anyone know what might be causing this?

Answer 1

// consider this method
-(void)populateArray {
WORef *ref = [WORef new];
ref.object = [YourObject new];
return #[ref];
// once you get out of this scope, the memory space occupied by [YourObject new]
// can be re-allocate to something else and your ref.object would still point at
// that memory space. You would get random crashes depending on when this memory space get re-allocated.
// The reason being is that ref.object hold a weak reference to [YourObject new]
// so it reference count doesn't get incremented.
// Change your property declaration to (nonatomic,strong) instead
}