return 0;
              case 1:
                return 1;
              case 2:
                return endOfData();
              default:
                throw new AssertionError("Should not have been invoked again");
            }
          }
        };

    assertTrue(iter.hasNext());
    assertEquals(0, (int) iter.next());

    // verify idempotence of hasNext()
    assertTrue(iter.hasNext());

                return 0;
              case 1:
                return 1;
              case 2:
                return endOfData();
              default:
                throw new AssertionError("Should not have been invoked again");
            }
          }
        };

    assertTrue(iter.hasNext());
    assertEquals(0, (int) iter.next());

    // verify idempotence of hasNext()
    assertTrue(iter.hasNext());

 *
 * @author Anthony Zana
 * @since 10.0
 */
@GwtCompatible
public interface FutureCallback<V extends @Nullable Object> {
  /** Invoked with the result of the {@code Future} computation when it is successful. */
  void onSuccess(@ParametricNullness V result);

  /**
   * Invoked when a {@code Future} computation fails or is canceled.
   *

   *
   * <p>Cancellation does not propagate from the output future to a callable that has begun to
   * execute, but if the output future is cancelled before {@link Callable#call()} is invoked,
   * {@link Callable#call()} will not be invoked.
   */
  public <T extends @Nullable Object> ListenableFuture<T> submit(
      Callable<T> callable, Executor executor) {
    checkNotNull(callable);
    checkNotNull(executor);

  /**
   * The maximum number of requests to execute concurrently. Above this requests queue in memory,
   * waiting for the running calls to complete.
   *
   * If more than [maxRequests] requests are in flight when this is invoked, those requests will
   * remain in flight.
   */
  @get:Synchronized
  var maxRequests = 64
    set(maxRequests) {
      require(maxRequests >= 1) { "max < 1: $maxRequests" }
      synchronized(this) {

                return 0;
              case 1:
                return 1;
              case 2:
                return endOfData();
              default:
                throw new AssertionError("Should not have been invoked again");
            }
          }
        };

    assertTrue(iter.hasNext());
    assertEquals(0, (int) iter.next());

    // verify idempotence of hasNext()
    assertTrue(iter.hasNext());

                return 0;
              case 1:
                return 1;
              case 2:
                return endOfData();
              default:
                throw new AssertionError("Should not have been invoked again");
            }
          }
        };

    assertTrue(iter.hasNext());
    assertEquals(0, (int) iter.next());

    // verify idempotence of hasNext()
    assertTrue(iter.hasNext());

   * {@code next}. Once the implementation either invokes {@code endOfData} or throws an exception,
   * {@code computeNext} is guaranteed to never be called again.
   *
   * <p>If this method throws an exception, it will propagate outward to the {@code hasNext} or
   * {@code next} invocation that invoked this method. Any further attempts to use the iterator will
   * result in an {@link IllegalStateException}.

   * Future} fails with the given {@code exceptionType}, from the result provided by the {@code
   * fallback}. {@link Function#apply} is not invoked until the primary input has failed, so if the
   * primary input succeeds, it is never invoked. If, during the invocation of {@code fallback}, an
   * exception is thrown, this exception is used as the result of the output {@code Future}.
   *
   * <p>Usage example:

   * <p>This method should return promptly; prefer to do work on a different thread where it is
   * convenient. It is invoked exactly once on service shutdown, even when {@link #stopAsync} is
   * called multiple times.
   *
   * <p>If {@link #stopAsync} is called on a {@link State#STARTING} service, this method is not
   * invoked immediately. Instead, it will be deferred until after the service is {@link