boolean[] called = new boolean[1];
    f.addCallback(
        new FutureCallback<String>() {
          @Override
          public void onSuccess(String result) {
            called[0] = true;
          }

          @Override
          public void onFailure(Throwable t) {}
        },
        directExecutor());
    assertThat(called[0]).isTrue();
  }

      @Override
      public int read(char[] cbuf, int off, int len) throws IOException {
        // if a buffer isn't being cleared correctly, this method will eventually start being called
        // with a len of 0 forever
        if (len <= 0) {
          fail("read called with a len of " + len);
        }
        // read fewer than the max number of chars to read
        // shouldn't be a problem unless the buffer is shrinking each call

      @Override
      public int read(char[] cbuf, int off, int len) throws IOException {
        // if a buffer isn't being cleared correctly, this method will eventually start being called
        // with a len of 0 forever
        if (len <= 0) {
          fail("read called with a len of " + len);
        }
        // read fewer than the max number of chars to read
        // shouldn't be a problem unless the buffer is shrinking each call

   *
   * <p>If a character has no mapped replacement then it is checked against the safe range. If it
   * lies outside that, then {@link #escapeUnsafe} is called, otherwise no escaping is performed.
   *
   * @param replacementMap a map of characters to their escaped representations
   * @param safeMin the lowest character value in the safe range

     * mirror, its URL and ID will be updated to match the values from the mirror specification. Repositories without a
     * matching mirror will pass through unchanged. Note: This method must be called before
     * {@link #injectAuthentication(List, List)} or the repositories will end up with the wrong credentials.
     *

    CLOSED,

    /**
     * {@link ClosingFuture#finishToValueAndCloser(ValueAndCloserConsumer, Executor)} has been
     * called. The step may not be further subsumed, nor may {@link #finishToFuture()} be called.
     */
    WILL_CREATE_VALUE_AND_CLOSER,
  }

func (s *Singleton[T]) IsSet() bool {
	select {
	case <-s.set:
		return true
	default:
		return false
	}
}

// Set the value and unblock all Get requests.
// This may only be called once, a second call will panic.
func (s *Singleton[T]) Set(v *T) {
	s.v = v
	close(s.set)

      /* TODO: verify that the Collection is also synchronized? */
      return delegate.values();
    }

    @Override
    public Set<Cell<R, C, V>> cellSet() {
      assertTrue(Thread.holdsLock(mutex));
      return delegate.cellSet();
    }

    @Override
    public Map<R, V> column(C columnKey) {
      assertTrue(Thread.holdsLock(mutex));
      return delegate.column(columnKey);
    }

    @Override
    protected Table<R, C, V> delegate() {
      return (Table<R, C, V>) delegate;
    }

    @Override
    public Set<Cell<R, C, V>> cellSet() {
      return Collections.unmodifiableSet(super.cellSet());
    }

    @Override
    public void clear() {
      throw new UnsupportedOperationException();
    }

    @Override

  @J2ktIncompatible
  @GwtIncompatible
    Object writeReplace() {
    Map<C, Integer> columnKeyToIndex = Maps.indexMap(columnKeySet());
    int[] cellColumnIndices = new int[cellSet().size()];
    int i = 0;
    for (Cell<R, C, V> cell : cellSet()) {
      // requireNonNull is safe because the cell exists in the table.
      cellColumnIndices[i++] = requireNonNull(columnKeyToIndex.get(cell.getColumnKey()));
    }