*/
    Waiter(boolean unused) {}

    Waiter() {
      // avoid volatile write, write is made visible by subsequent CAS on waiters field
      ATOMIC_HELPER.putThread(this, Thread.currentThread());
    }

    // non-volatile write to the next field. Should be made visible by subsequent CAS on waiters
    // field.
    void setNext(@CheckForNull Waiter next) {