final FileEntry itm = results[this.ridx];
            this.ridx++;
            if (filter(itm)) {
                return itm;
            }
        }

        if (!last && !isDone()) {
            if (!fetchMore()) {
                doClose();
                return null;
            }
            this.ridx = 0;
            return advance(true);
        }
        return null;

 *
 * @since 20.0
 */
@GwtCompatible
public interface AsyncCallable<V extends @Nullable Object> {
  /**
   * Computes a result {@code Future}. The output {@code Future} need not be {@linkplain
   * Future#isDone done}, making {@code AsyncCallable} suitable for asynchronous derivations.
   *
   * <p>Throwing an exception from this method is equivalent to returning a failing {@link
   * ListenableFuture}.
   */

   * does not include "was cancelled." To be explicit: If this method returns a non-null value,
   * then:
   *
   * <ul>
   *   <li>{@code isDone()} must return {@code true}
   *   <li>{@code isCancelled()} must return {@code false}
   *   <li>{@code get()} must not block, and it must throw an {@code ExecutionException} with the

import org.jspecify.annotations.Nullable;

/**
 * A {@link Future} that accepts completion listeners. Each listener has an associated executor, and
 * it is invoked using this executor once the future's computation is {@linkplain Future#isDone()
 * complete}. If the computation has already completed when the listener is added, the listener will
 * execute immediately.
 *
 * <p>See the Guava User Guide article on <a

import org.jspecify.annotations.Nullable;

/**
 * A {@link Future} that accepts completion listeners. Each listener has an associated executor, and
 * it is invoked using this executor once the future's computation is {@linkplain Future#isDone()
 * complete}. If the computation has already completed when the listener is added, the listener will
 * execute immediately.
 *
 * <p>See the Guava User Guide article on <a

   * TimeUnit)} overload in order to test that method.
   */
  static <V extends @Nullable Object> V getDoneFromTimeoutOverload(Future<V> future)
      throws ExecutionException {
    checkState(future.isDone(), "Future was expected to be done: %s", future);
    try {
      return getUninterruptibly(future, 0, SECONDS);
    } catch (TimeoutException e) {
      throw new AssertionError(e);
    }
  }

    // There is no thread interruption in GWT, so there's nothing to do.
  }

  static <V extends @Nullable Object> V getDoneFromTimeoutOverload(Future<V> future)
      throws ExecutionException {
    checkState(future.isDone(), "Future was expected to be done: %s", future);
    try {
      return future.get(0, SECONDS);
    } catch (InterruptedException e) {
      throw new AssertionError();
    } catch (TimeoutException e) {

   * does not include "was cancelled." To be explicit: If this method returns a non-null value,
   * then:
   *
   * <ul>
   *   <li>{@code isDone()} must return {@code true}
   *   <li>{@code isCancelled()} must return {@code false}
   *   <li>{@code get()} must not block, and it must throw an {@code ExecutionException} with the

   * TimeUnit)} overload in order to test that method.
   */
  static <V extends @Nullable Object> V getDoneFromTimeoutOverload(Future<V> future)
      throws ExecutionException {
    checkState(future.isDone(), "Future was expected to be done: %s", future);
    try {
      return getUninterruptibly(future, 0, SECONDS);
    } catch (TimeoutException e) {
      throw new AssertionError(e);
    }
  }

    // stop it.
    blockingCallable.waitForStart();

    // Give the second task a chance to (incorrectly) start up while the first task is running.
    assertThat(future2.isDone()).isFalse();

    // Stop the first task. The second task should then run.
    blockingCallable.stop();
    executor.shutdown();
    assertThat(executor.awaitTermination(10, SECONDS)).isTrue();