/**
   * Returns a view of the entries stored in this cache as a thread-safe map. Modifications made to
   * the map directly affect the cache.
   *
   * <p>Iterators from the returned map are at least <i>weakly consistent</i>: they are safe for
   * concurrent use, but if the cache is modified (including by eviction) after the iterator is
   * created, it is undefined which of the changes (if any) will be reflected in that iterator.
   *

     * However, serialization does not preserve that property, though it does maintain the key and
     * value ordering.
     *
     * @since 8.0
     */
    // TODO: Make serialization behavior consistent.
    @CanIgnoreReturnValue
    @Override
    public Builder<K, V> orderValuesBy(Comparator<? super V> valueComparator) {
      super.orderValuesBy(valueComparator);
      return this;
    }

  /**
   * Returns an immutable bimap containing the same entries as {@code map}. If {@code map} somehow
   * contains entries with duplicate keys (for example, if it is a {@code SortedMap} whose
   * comparator is not <i>consistent with equals</i>), the results of this method are undefined.
   *
   * <p>The returned {@code BiMap} iterates over entries in the same order as the {@code entrySet}
   * of the original map.
   *

     * an int.
     */
    checkNonNegative("a", a);
    checkNonNegative("b", b);
    if (a == 0) {
      // 0 % b == 0, so b divides a, but the converse doesn't hold.
      // BigInteger.gcd is consistent with this decision.
      return b;
    } else if (b == 0) {
      return a; // similar logic
    }
    /*
     * Uses the binary GCD algorithm; see http://en.wikipedia.org/wiki/Binary_GCD_algorithm. This is

   *
   * <p><b>Warning:</b> contrary to the typical assumptions about predicates (as documented at
   * {@link Predicate#apply}), the returned predicate may not be <i>consistent with equals</i>. For
   * example, {@code instanceOf(ArrayList.class)} will yield different results for the two equal
   * instances {@code Lists.newArrayList(1)} and {@code Arrays.asList(1)}.
   */

   *
   * <p><b>Warning:</b> {@code keyPredicate} must be <i>consistent with equals</i>, as documented at
   * {@link Predicate#apply}. Do not provide a predicate such as {@code
   * Predicates.instanceOf(ArrayList.class)}, which is inconsistent with equals.
   */
  public static <K extends @Nullable Object, V extends @Nullable Object> Map<K, V> filterKeys(

 * equality for both keys and values. This may not be the desired behavior for map implementations
 * that use non-standard notions of key equality, such as a {@code SortedMap} whose comparator is
 * not consistent with {@code equals}.
 *
 * <p>The {@code standard} methods and the collection views they return are not guaranteed to be
 * thread-safe, even when all of the methods that they depend on are thread-safe.
 *

   * without grabbing the lock.
   *
   * <p>To update this field correctly the lock must be held to guarantee that the state is
   * consistent.
   */
  private volatile StateSnapshot snapshot = new StateSnapshot(NEW);

  /** Constructor for use by subclasses. */
  protected AbstractService() {}

  /**

          !item.equals(NotAnInstance.EQUAL_TO_NOTHING));
      assertTrue(item + " must be Object#equals to itself", item.equals(item));
      assertEquals(
          "the Object#hashCode of " + item + " must be consistent",
          item.hashCode(),
          item.hashCode());
      if (!(item instanceof String)) {
        assertTrue(
            item + " must not be Object#equals to its Object#toString representation",

  /**
   * Returns an immutable map containing the same entries as {@code map}. If {@code map} somehow
   * contains entries with duplicate keys (for example, if it is a {@code SortedMap} whose
   * comparator is not <i>consistent with equals</i>), the results of this method are undefined.
   *
   * <p><b>Note:</b> Despite what the method name suggests, if {@code map} is an {@code
   * ImmutableClassToInstanceMap}, no copy will actually be performed.