class ChunkOperation : AsyncOperation
{
      ...

    init(..) {
      .....
    }

    override func cancel() {
        task.cancel()
        super.cancel()
    }

    override func main() {
        guard  !isCancelled else { return  }

        guard  let dependencyID = dependencies .compactMap({ ($0 as? FirstOperation)?.xxx }).first else { return  }

        task = session.uploadTask(with: ., fromFile: ..)
        task.resume()
    }
}