code: public boolean cancel(T task) {
      CancellableTask<K, T> cancellableTask = this.cancellableTaskMap.getIfPresent(task.getKey());
      if (cancellableTask != null && cancellableTask.getScheduledTask() == task && cancellableTask.cancel()) {
        this.cancellableTaskMap.invalidate(task.getKey());
        return true;
      }
      return false;
    }
docs: Attempts to cancel the specified {@link ScheduledTask}.
  
  @param task the {@link ScheduledTask} to cancel
  @return true if the {@link ScheduledTask} was canceled; otherwise, false