* elements from each bin must either stay at same index, or move with a power of two offset.
       * We eliminate unnecessary node creation by catching cases where old nodes can be reused
       * because their next fields won't change. Statistically, at the default threshold, only
       * about one-sixth of them need cloning when a table doubles. The nodes they replace will be

    @Override
    Listener gasListeners(AbstractFuture<?> future, Listener update) {
      synchronized (future) {
        Listener old = future.listeners;
        if (old != update) {
          future.listeners = update;
        }
        return old;
      }
    }

    /** Performs a GAS operation on the {@link #waiters} field. */
    @Override

    @Override
    Listener gasListeners(AbstractFuture<?> future, Listener update) {
      synchronized (future) {
        Listener old = future.listeners;
        if (old != update) {
          future.listeners = update;
        }
        return old;
      }
    }

    /** Performs a GAS operation on the {@link #waiters} field. */
    @Override

   * possible pair of these futures in {@link FuturesTest#runExtensiveMergerTest}.
   *
   * <p>Each test requires a new {@link TestFutureBatch} because we need new delayed futures each
   * time, as the old delayed futures were completed as part of the old test.
   */
  @J2ktIncompatible
  @GwtIncompatible // used only in GwtIncompatible tests
  private static final class TestFutureBatch {

   * possible pair of these futures in {@link FuturesTest#runExtensiveMergerTest}.
   *
   * <p>Each test requires a new {@link TestFutureBatch} because we need new delayed futures each
   * time, as the old delayed futures were completed as part of the old test.
   */
  @J2ktIncompatible
  @GwtIncompatible // used only in GwtIncompatible tests
  private static final class TestFutureBatch {

              // if checkTime, we want to check *after* acquiring the lock if refresh still needs
              // to be scheduled
              return null;
            }

            // continue returning old value while loading
            ++modCount;
            LoadingValueReference<K, V> loadingValueReference =
                new LoadingValueReference<>(valueReference);

      if (lastKnownIndex == -1) {
        put(key, value);
        return unsafeNull(); // See discussion in getValue().
      } else {
        V old = value(lastKnownIndex);
        CompactHashMap.this.setValue(lastKnownIndex, value);
        return old;
      }
    }
  }

  @Override
  public int size() {
    Map<K, V> delegate = delegateOrNull();

    @J2ktIncompatible // serialization
    @GwtIncompatible // serialization
    Object writeReplace() {
      return super.writeReplace();
    }

    // No longer used for new writes, but kept so that old data can still be read.
    @GwtIncompatible // serialization
    @J2ktIncompatible
    @SuppressWarnings("unused")
    private static class SerializedForm<K> implements Serializable {
      final ImmutableMap<K, ?> map;

    }

    moveLastEntry(index, mask);
    size--;
    incrementModCount();

    return true;
  }

  /**
   * Moves the last entry in the entry array into {@code dstIndex}, and nulls out its old position.
   */
  void moveLastEntry(int dstIndex, int mask) {
    Object table = requireTable();
    int[] entries = requireEntries();
    @Nullable Object[] elements = requireElements();

   * normally derive from {@code Map<Object, Object>}, but they typically contain strings, which is
   * awkward. This method lets you get a plain-old-{@code Map} out of a {@code Properties}.
   *
   * @param properties a {@code Properties} object to be converted
   * @return an immutable map containing all the entries in {@code properties}