}

      while (true) {
        int oldValue = existingCounter.get();
        if (oldValue != 0) {
          try {
            int newValue = IntMath.checkedAdd(oldValue, occurrences);
            if (existingCounter.compareAndSet(oldValue, newValue)) {
              // newValue can't == 0, so no need to check & remove
              return oldValue;
            }