}
    }

    void addListener(Listener listener, Executor executor) {
      listeners.addListener(listener, executor);
    }

    void awaitHealthy() {
      monitor.enterWhenUninterruptibly(awaitHealthGuard);
      try {
        checkHealthy();
      } finally {
        monitor.leave();
      }
    }

    void awaitHealthy(long timeout, TimeUnit unit) throws TimeoutException {

   * @return whether the monitor was entered, which guarantees that the guard is now satisfied
   * @since 28.0 (but only since 33.4.0 in the Android flavor)
   */
  public boolean enterWhenUninterruptibly(Guard guard, Duration time) {
    return enterWhenUninterruptibly(guard, toNanosSaturated(time), TimeUnit.NANOSECONDS);
  }

  /**
   * Enters this monitor when the guard is satisfied. Blocks at most the given time, including both