Boost Asio，異步UDP客戶端-關機時崩潰

Question

我在應用程序中將UDP客戶端服務器用於IPC

它工作正常，但是當嘗試關閉客戶端時，會發生一些競爭情況，這會導致應用程序崩潰或死鎖。

UDP客戶端：

// IOServiceBase class contain boost::asio::io_service instance
// it is accessible by service() protected method
class AsyncUDPClient : public IOServiceBase
{
public:

    /// @brief Create a network client
    AsyncUDPClient(const std::string& host, const std::string port)
        : _host(host)
        , _port(port)
        , _reply()
        , _work(service())
        , _sock(service(), ba_ip::udp::endpoint(ba_ip::udp::v4(), 0)) {

        run();
    }

    /// @brief Start async packets processing
    void run(){
        std::thread t([&]{ service().run(); });
        t.detach();
    }

    /// @brief Async request to server
    void send(uint8_t* message, size_t length) {
        std::vector<uint8_t> packet(message, message + length);
        service().post(boost::bind(&AsyncUDPClient::do_send, this, packet));
    }

    /// @brief Cleanup io_service to dismiss already putted tasks
    ~AsyncUDPClient() {
        close();

        // trying to wait until service is stopped, but it does not help
        while (!service().stopped()){
            std::this_thread::sleep_for(std::chrono::milliseconds(100));
        }
    }

    /// @brief Cleanup io_service to dismiss already putted tasks
    void close(){
        std::thread t([&]{ service().stop(); });
        t.join();
    }
protected:

// send-response methods are pretty standard

private:

    std::string _host;
    std::string _port;
    std::array<uint8_t, max_length> _reply;
    ba::io_service::work _work;
    ba_ip::udp::socket _sock;
};

用法示例：

{
    AsyncUDPClient ipc(addr, port);
    ipc.send(&archive_data[0], archive_data.size());
    // it seems client is destroyed before some internal processing is finished?
}

行為不是確定性的，有時工作正常，有時崩潰，有時凍結。 Stacktrace在boost.asio內部的某個地方顯示崩潰點

Answer 1

銷毀AsyncUDPClient無法與運行io_service的線程正確同步。 當處理io_service的線程在其生命周期結束后嘗試與AsyncUDPClient及其io_service進行交互時，這可能導致調用未定義的行為。

要解決此問題，請不要與處理io_service的線程分離，並在io_service停止后顯式加入線程。

class AsyncUDPClient
 : public IOServiceBase
{
public:

  // ...

  void run()
  {
    _threads.emplace_back([&]{ service().run(); })
  }

  // ...

  ~AsyncUDPClient()
  {
    close();
  }

  void close()
  {
    // Stop the io_service.  This changes its state and return immediately.
    service().stop();

    // Explicitly synchronize with threads running the io_service.
    for (auto& thread: _threads)
    {
      thread.join();
    }
  }

private:

  // ...
  std::vector<std::thread> _threads;
};

如以上注釋所暗示， io_service::stop()不會阻止。 它將io_service的狀態更改為已停止，立即返回，並使run()和run_one()所有調用盡快返回。 調用io_service::stopped()立即返回io_service的狀態。 這些調用均未指示在run()或run_one()的調用中是否存在線程。