Is dealloc guaranteed to be called on the same thread that created the object?

Question

Is dealloc guaranteed to be called on the same thread that created a NSObject instance? For example, if I call [[MyFluffyBunny alloc] init]

Answer 1

There is no such guarantee and, in fact, it makes for some subtle bugs when using KVO (and bindings on OS X).

You can see it in action fairly easily by creating an object that logs [NSThread currentThread] during init and dealloc, then running code such as:

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    Testing *testing = [[Testing alloc] init];
    dispatch_async(dispatch_get_global_queue(QOS_CLASS_BACKGROUND, 0), ^{
        NSLog(@"Use testing in background: %@", testing);
    });
    testing = nil;
    return YES;
}