* common bugs: The {@code wait()} must be inside a {@code while} instead of an {@code if}, and
 * {@code notifyAll()} must be used instead of {@code notify()} because there are two different
 * logical conditions being awaited.
 *
 * <pre>{@code
 * public class SafeBox<V> {
 *   private V value;
 *
 *   public synchronized V get() throws InterruptedException {

     * <p>{@code value} may be null only for a loading reference.
     */
    ValueReference<K, V> copyFor(
        ReferenceQueue<V> queue, @CheckForNull V value, ReferenceEntry<K, V> entry);

    /**
     * Notify pending loads that a new value was set. This is only relevant to loading value
     * references.
     */
    void notifyNewValue(@CheckForNull V newValue);

    /**

    if (ticker != null) {
      return ticker;
    }
    return recordsTime ? Ticker.systemTicker() : NULL_TICKER;
  }

  /**
   * Specifies a listener instance that caches should notify each time an entry is removed for any
   * {@linkplain RemovalCause reason}. Each cache created by this builder will invoke this listener
   * as part of the routine maintenance described in the class documentation above.
   *

 *           // Services have been initialized and are healthy, start accepting requests...
 *         }
 *         public void failure(Service service) {
 *           // Something failed, at this point we could log it, notify a load balancer, or take
 *           // some other action.  For now we will just exit.
 *           System.exit(1);
 *         }
 *       },
 *       MoreExecutors.directExecutor());
 *

    if (ticker != null) {
      return ticker;
    }
    return recordsTime ? Ticker.systemTicker() : NULL_TICKER;
  }

  /**
   * Specifies a listener instance that caches should notify each time an entry is removed for any
   * {@linkplain RemovalCause reason}. Each cache created by this builder will invoke this listener
   * as part of the routine maintenance described in the class documentation above.
   *

     * <p>{@code value} may be null only for a loading reference.
     */
    ValueReference<K, V> copyFor(
        ReferenceQueue<V> queue, @CheckForNull V value, ReferenceEntry<K, V> entry);

    /**
     * Notify pending loads that a new value was set. This is only relevant to loading value
     * references.
     */
    void notifyNewValue(@CheckForNull V newValue);

    /**