} catch (ExecutionException e) {
      builder.append("FAILURE, cause=[").append(e.getCause()).append("]");
    } catch (CancellationException e) {
      builder.append("CANCELLED");
    } catch (RuntimeException e) {
      builder.append("UNKNOWN, cause=[").append(e.getClass()).append(" thrown from get()]");
    }
  }

  private enum State {
    PENDING {

      }
    }

    final boolean wasInterrupted;
    @CheckForNull final Throwable cause;

    Cancellation(boolean wasInterrupted, @CheckForNull Throwable cause) {
      this.wasInterrupted = wasInterrupted;
      this.cause = cause;
    }
  }

  /** A special value that encodes the 'setFuture' state. */