An example of how to track / count live instances of a particular class.

LiveInstanceTracking.m

@implementation LiveInstanceTracking

static NSHashTable *instances;

- (instancetype)init {
    self = [super init];
    if (self) {
        if (!instances) {
            instances = [[NSHashTable alloc] initWithOptions:NSHashTableWeakMemory capacity:1000];
        }
        [instances addObject:self];
    }
    return self;
}

- (void)dealloc {
    [instances removeObject:self];
}

@end

Note: This is slightly simplified: use dispatch_onceto create the NSHashTable if in a threaded environment.