* 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

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");

  static <V extends @Nullable Object> V get(AbstractFuture<V> future)
      throws InterruptedException, ExecutionException {
    return future.getFromAlreadyDoneTrustedFuture();
  }

  static <V extends @Nullable Object> V get(AbstractFuture<V> future, long timeout, TimeUnit unit)
      throws InterruptedException, ExecutionException, TimeoutException {
    checkNotNull(unit);
    return future.getFromAlreadyDoneTrustedFuture();
  }

          }
        };

    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();

          }

          @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;

  }

  /**
   * 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;
    }

  static final OtherThrowable OTHER_THROWABLE = new OtherThrowable();
  static final Future<String> FAILED_FUTURE_OTHER_THROWABLE =
      immediateFailedFuture(OTHER_THROWABLE);
  static final Error ERROR = new Error("mymessage");
  static final Future<String> FAILED_FUTURE_ERROR = immediateFailedFuture(ERROR);
  static final Future<String> RUNTIME_EXCEPTION_FUTURE =
      UncheckedThrowingFuture.throwingRuntimeException(RUNTIME_EXCEPTION);

@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>If the future's {@link Future#get() get} method throws an {@link ExecutionException}, then