asio::async_write 和链-C/C++问题

asio::async_write and strand(asio::async_write 和链)

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问题描述

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

这段代码是否保证async_write内部的所有异步操作处理程序(调用async_write_some)都通过strand调用?(或者它只是为了 my_handler?)

Does this code guarantee that all asynchronous operation handlers(calls to async_write_some) inside async_write are called through strand? (or it's just for my_handler?)

推荐答案

使用以下代码:

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

对于这个组合操作，如果以下所有条件都为真，所有对 stream.async_write_some() 的调用都将在 m_strand 内调用:

For this composed operation, all calls to stream.async_write_some() will be invoked within m_strand if all of the following conditions are true:

发起的 async_write(...) 调用在 m_strand() 中运行:

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

custom_alloc 的返回类型是:

从 strand::wrap()

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

一个自定义处理程序，用于适当链接 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};
}

请参阅此答案以了解有关链的更多详细信息，以及this 回答有关 asio_handler_invoke 的详细信息.

See this answer for more details on strands, and this answer for details on asio_handler_invoke.

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