Method UnregisterHandlers

cpp/src/arrow/util/cancel.cc:167–174

  }

  void UnregisterHandlers() {
    std::lock_guard<std::mutex> lock(mutex_);
    self_pipe_ptr_.store(nullptr);
    auto handlers = std::move(saved_handlers_);
    for (const auto& h : handlers) {
      ARROW_CHECK_OK(SetSignalHandler(h.signum, h.handler));
    }
  }

  ~SignalStopState() {
    atfork_handler_.reset();