* CacheBuilder#refreshAfterWrite}, or through a call to {@link LoadingCache#refresh}.
   *
   * <p>This implementation synchronously delegates to {@link #load}. It is recommended that it be
   * overridden with an asynchronous implementation when using {@link
   * CacheBuilder#refreshAfterWrite}.
   *
   * <p><b>Note:</b> <i>all exceptions thrown by this method will be logged and then swallowed</i>.

   * CacheBuilder#refreshAfterWrite}, or through a call to {@link LoadingCache#refresh}.
   *
   * <p>This implementation synchronously delegates to {@link #load}. It is recommended that it be
   * overridden with an asynchronous implementation when using {@link
   * CacheBuilder#refreshAfterWrite}.
   *
   * <p><b>Note:</b> <i>all exceptions thrown by this method will be logged and then swallowed</i>.

   * response to the sender.
   *
   * @since 8.0
   */
  public static final byte NAK = 21;

  /**
   * Synchronous Idle: A communication control character used by a synchronous transmission system
   * in the absence of any other character to provide a signal from which synchronism may be
   * achieved or retained.
   *
   * @since 8.0
   */

   * CacheLoader#reload}.
   *
   * <p>As the default implementation of {@link CacheLoader#reload} is synchronous, it is
   * recommended that users of this method override {@link CacheLoader#reload} with an asynchronous
   * implementation; otherwise refreshes will be performed during unrelated cache read and write
   * operations.
   *

   * response to the sender.
   *
   * @since 8.0
   */
  public static final byte NAK = 21;

  /**
   * Synchronous Idle: A communication control character used by a synchronous transmission system
   * in the absence of any other character to provide a signal from which synchronism may be
   * achieved or retained.
   *
   * @since 8.0
   */

   * CacheLoader#reload}.
   *
   * <p>As the default implementation of {@link CacheLoader#reload} is synchronous, it is
   * recommended that users of this method override {@link CacheLoader#reload} with an asynchronous
   * implementation; otherwise refreshes will be performed during unrelated cache read and write
   * operations.
   *

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}.
   */
  ListenableFuture<V> call() throws Exception;

  /**
   * Returns an output {@code Future} to use in place of the given {@code input}. The output {@code
   * Future} need not be {@linkplain Future#isDone done}, making {@code AsyncFunction} suitable for
   * asynchronous derivations.
   *
   * <p>Throwing an exception from this method is equivalent to returning a failing {@code Future}.
   */
  ListenableFuture<O> apply(@ParametricNullness I input) throws Exception;

   * currently contains a value for {@code key}, and {@link CacheLoader#load} otherwise. Loading is
   * asynchronous only if {@link CacheLoader#reload} was overridden with an asynchronous
   * implementation.
   *
   * <p>Returns without doing anything if another thread is currently loading the value for {@code

     * another thread or the worker task has cleared the count and set the state.
     *
     * <p>When {@link #executor} is a directExecutor(), the value written to
     * {@code workerRunningState} will be available synchronously, and behaviour will be
     * deterministic.
     */
    @SuppressWarnings("GuardedBy")
    boolean alreadyMarkedQueued = workerRunningState != QUEUING;
    if (alreadyMarkedQueued) {
      return;
    }