*
   * @since 10.0
   */
  public abstract static class Guard {

    @Weak final Monitor monitor;
    final Condition condition;

    @GuardedBy("monitor.lock")
    int waiterCount = 0;

    /** The next active guard */
    @GuardedBy("monitor.lock")
    @Nullable Guard next;

    protected Guard(Monitor monitor) {
      this.monitor = checkNotNull(monitor, "monitor");