// longer than necessary.
        submitting = null;
      }
    }

    @SuppressWarnings("ShortCircuitBoolean")
    @Override
    public void run() {
      Thread currentThread = Thread.currentThread();
      if (currentThread != submitting) {
        /*
         * requireNonNull is safe because we set `task` before submitting this Runnable to an

   * functionality.
   *
   * <p><b>Warning:</b> If the input future does not already implement {@code ListenableFuture}, the
   * returned future will emulate {@link ListenableFuture#addListener} by submitting a task to the
   * given executor at the first call to {@code addListener}. The task must be started by the
   * executor promptly, or else the returned {@code ListenableFuture} may fail to work. The task's

    /** Accepts a {@link ValueAndCloser} for the last step in a {@link ClosingFuture} pipeline. */
    void accept(ValueAndCloser<V> valueAndCloser);
  }

  /**
   * Starts a {@link ClosingFuture} pipeline by submitting a callable block to an executor.
   *
   * @throws java.util.concurrent.RejectedExecutionException if the task cannot be scheduled for
   *     execution
   */

    /** Accepts a {@link ValueAndCloser} for the last step in a {@link ClosingFuture} pipeline. */
    void accept(ValueAndCloser<V> valueAndCloser);
  }

  /**
   * Starts a {@link ClosingFuture} pipeline by submitting a callable block to an executor.
   *
   * @throws java.util.concurrent.RejectedExecutionException if the task cannot be scheduled for
   *     execution
   */