asio :: async_write和strand

Question

asio::async_write(m_socket, asio::buffer(buf, bytes),
                custom_alloc(m_strand.wrap(custom_alloc(_OnSend))));

此代码是否保证async_write中的所有异步操作处理程序(对async_write_some的调用)都是通过strand调用的？(或者只是为了my_handler？)

Answer 1

使用以下代码:

asio::async_write(stream, ..., custom_alloc(m_strand.wrap(...)));

对于此组合操作,如果满足以下所有条件,stream.async_write_some()则将调用所有调用m_strand:

• 发起async_write(...)呼叫在m_strand()以下内容中运行:

  assert(m_strand.running_in_this_thread());
  asio::async_write(stream, ..., custom_alloc(m_strand.wrap(...)));
  

• 返回类型custom_alloc是:

  • 返回的确切类型 strand::wrap()

    template <typename Handler> 
    Handler custom_alloc(Handler) { ... }
    

  • 适合链调用的自定义处理程序asio_handler_invoke():

    template <class Handler>
    class custom_handler
    {
    public:
      custom_handler(Handler handler)
        : handler_(handler)
      {}
    
      template <class... Args>
      void operator()(Args&&... args)
      {
        handler_(std::forward<Args>(args)...);
      }
    
      template <typename Function>
      friend void asio_handler_invoke(
        Function intermediate_handler,
        custom_handler* my_handler)
      {
        // Support chaining custom strategies incase the wrapped handler
        // has a custom strategy of its own.
        using boost::asio::asio_handler_invoke;
        asio_handler_invoke(intermediate_handler, &my_handler->handler_);
      }
    
    private:
      Handler handler_;
    };
    
    template <typename Handler>
    custom_handler<Handler> custom_alloc(Handler handler)
    {
      return {handler};
    }
    

见这个答案对绞线的详细信息,以及这个答案的详细信息asio_handler_invoke.