}

  /**
   * Waits until the given future {@linkplain Future#isDone is done}, invoking the garbage collector
   * as necessary to try to ensure that this will happen.
   *
   * @throws RuntimeException if timed out or interrupted while waiting
   */
  @SuppressWarnings("removal") // b/260137033
  public static void awaitDone(Future<?> future) {
    if (future.isDone()) {
      return;
    }

import java.util.concurrent.Executor;
import java.util.concurrent.Future;
import java.util.concurrent.RejectedExecutionException;
import org.jspecify.annotations.NullMarked;
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()

      MockExecutor mock = new MockExecutor();
      TestExecutor testExecutor = new TestExecutor(mock);
      Future<?> f = testExecutor.submit(doNothing());
      mock.assertLastMethodCalled("submit");
      f.get();
    }
    {
      MockExecutor mock = new MockExecutor();
      TestExecutor testExecutor = new TestExecutor(mock);
      Future<String> f = testExecutor.submit(doNothing(), RESULT_VALUE);
      mock.assertLastMethodCalled("submit");

     * Future, then a call setException() would likely also overflow.
     *
     * - If the stack overflowed after set()/setValue() stored its result, then a call to
     * setException() will be a no-op because the Future is already done.
     *
     * Both scenarios are bad: The output Future might never complete, or, if it does complete, it

    delegate().execute(command);
  }

  @Override
  public <T extends @Nullable Object> Future<T> submit(Callable<T> task) {
    return delegate().submit(task);
  }

  @Override
  public Future<?> submit(Runnable task) {
    return delegate().submit(task);
  }

  @Override
  public <T extends @Nullable Object> Future<T> submit(
      Runnable task, @ParametricNullness T result) {

          }
        };

    AsyncCallable<String> asyncCallable =
        Callables.asAsyncCallable(callable, newDirectExecutorService());

    ListenableFuture<String> future = asyncCallable.call();
    assertSame(expected, future.get());
  }

  @J2ktIncompatible
  @GwtIncompatible
  public void testAsAsyncCallable_exception() throws Exception {
    Exception expected = new IllegalArgumentException();

 * result.
 *
 * @since 20.0
 */
@FunctionalInterface
@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

    Listener old = listeners;
    listeners = update;
    return old;
  }

  static boolean casValue(AbstractFutureState<?> future, @Nullable Object expect, Object update) {
    if (future.value == expect) {
      future.value = update;
      return true;
    }
    return false;
  }

  final @Nullable Object value() {
    return value;
  }

          }

          @Override
          public void onFailure(Throwable t) {
            failureCalls[0]++;
          }
        };
    addCallback(future, callback, directExecutor());
    future.set(result);
    assertEquals(result, future.get());
    assertThat(successCalls[0]).isEqualTo(1);
    assertThat(failureCalls[0]).isEqualTo(0);
  }

  public void testOnSuccessThrowsError() throws Exception {

    /**
     * Contains the most recently submitted {@code Future}, which may be cancelled or updated,
     * always under a lock.
     */
    private static final class SupplantableFuture implements Cancellable {
      private final ReentrantLock lock;

      @GuardedBy("lock")
      private Future<@Nullable Void> currentFuture;

      SupplantableFuture(ReentrantLock lock, Future<@Nullable Void> currentFuture) {
        this.lock = lock;