Question

我的程序总是使用依赖于平台的同步接收，它会阻止执行直到超时或接收事件，如：

recv(buf, size, timeout);

现在我想用boost替换这个代码以使其跨平台。我找到了解决方案，但我觉得这很难看（与单一函数调用相比）。我写了这个：

void IPV4_HOST::recv_timer_handler(const boost::system::error_code & e)
{
    if (e.value() == boost::system::errc::success) {
        f_recv_timeout = true;
        asio_socket.cancel();
    }
}

void IPV4_HOST::recv_handler(const boost::system::error_code & , size_t bytes)
{
    recv_timer.cancel();
    bytes_received = bytes;
}

int IPV4_HOST::receive(void * buf, size_t buf_size, TIME::INTERVAL timeout)
{
    f_recv_timeout = false;
    bytes_received = 0;

    recv_timer.expires_from_now(timeout.get_boost_milli());
    recv_timer.async_wait(boost::bind(&IPV4_HOST::recv_timer_handler, this, boost::asio::placeholders::error));

    asio_socket.async_read_some(boost::asio::buffer(buf, buf_size),
                                boost::bind(&IPV4_HOST::recv_handler, this, boost::asio::placeholders::error, boost::asio::placeholders::bytes_transferred));

    io_service.run();

    if (f_recv_timeout)
        throw IO::TimeoutReceiveException();

    return bytes_received;
}

你能告诉我，我做得对吗？有更简单的方法吗？

Answer 1

这是正确的方向，但有一些微妙的要点需要考虑：

如果将任何其他作品发布到io_service，则IPV4_HOST::receive()将开始处理该作品。
当io_service::run()在正常情况下返回时，暗示io_service已停止。除非io_service为reset()，否则对run()，run_one()，poll()或poll_one()的后续调用将立即返回。
两个异步操作可以同时完成，使两个完成处理程序都可以成功运行。 deadline_timer::cancel()的备注部分强调了这种行为;但是，所有异步操作都显示此behavior。在现有代码中，当IO::TimeoutReceiveException大于零时，这会导致bytes_received被抛出。

处理io_service详细信息的一种解决方案，以及使用完成处理程序执行的非确定性顺序，可能如下所示：

void IPV4_HOST::recv_timer_handler(const boost::system::error_code & e)
{
  timer_handled = true;
  if (!e) {
    f_recv_timeout = true;
    asio_socket.cancel();
  }
}

void IPV4_HOST::recv_handler(const boost::system::error_code &,
                             size_t bytes)
{
  recv_handled = true;
  recv_timer.cancel();
  bytes_received = bytes;
}

int IPV4_HOST::receive(void * buf, size_t buf_size, TIME::INTERVAL timeout)
{
  timer_handled  = false;
  recv_handled   = false;
  f_recv_timeout = false;
  bytes_received = 0;

  recv_timer.expires_from_now(timeout.get_boost_milli());
  recv_timer.async_wait(
    boost::bind(&IPV4_HOST::recv_timer_handler, this,
                boost::asio::placeholders::error));

  asio_socket.async_read_some(
    boost::asio::buffer(buf, buf_size),
    boost::bind(&IPV4_HOST::recv_handler, this, 
                boost::asio::placeholders::error,
                boost::asio::placeholders::bytes_transferred));

  // If a handler has not ran, then keep processing work on the io_service.
  // We need to consume both handlers so that old handlers are not in the
  // io_service the next time receive is called.
  while (!timer_handled || !recv_handled)
  {
    io_service.run_one();
  }

  // If the io_service has stopped (due to running out of work), then reset
  // it so that it can be run on next call to receive.
  if (io_service.stopped())
    io_service.reset();

  // If no bytes were received and the timeout occurred, then throw.  This
  // handles the case where both a timeout and receive occurred at the 
  // same time.
  if (!bytes_received && f_recv_timeout)
    throw IO::TimeoutReceiveException();

  return bytes_received;
}

此外，在尝试获取跨平台行为时，请阅读basic_stream_socket::cancel()的注释。有一些平台特定的行为需要注意。

async_read_some模拟同步超时接收

1 个答案: