code: public static <T> long addCap(AtomicLongFieldUpdater<T> updater, T instance, long toAdd) {
  		long r, u;
  		for (;;) {
  			r = updater.get(instance);
  			if (r == Long.MAX_VALUE) {
  				return Long.MAX_VALUE;
  			}
  			u = addCap(r, toAdd);
  			if (updater.compareAndSet(instance, r, u)) {
  				return r;
  			}
  		}
  	}
docs: Concurrent addition bound to Long.MAX_VALUE.
  Any concurrent write will "happen before" this operation.
  
  @param <T> the parent instance type
  @param updater  current field updater
  @param instance current instance to update
  @param toAdd    delta to add
  @return value before addition or Long.MAX_VALUE