protected void interruptTask() {
    CombinedFutureInterruptibleTask<?> localTask = task;
    if (localTask != null) {
      localTask.interruptTask();
    }
  }

  @WeakOuter
  private abstract class CombinedFutureInterruptibleTask<T extends @Nullable Object>
      extends InterruptibleTask<T> {
    private final Executor listenerExecutor;

    CombinedFutureInterruptibleTask(Executor listenerExecutor) {