为 boost socket.connect 设置超时

Question

我在tcp::socket 上使用boost::asio::connect。当一切正常时，connect 立即返回，但在网络不佳时，connect 在等待 15 秒的日志后超时。我不能等那么久，所以想减少超时。不幸的是，到目前为止我还没有遇到任何解决方案。

我看到了 async_wait 与deadline_timer 一起使用的解决方案，但所有这些示例都用于接收/发送操作，而不是用于连接。

谁能帮我提供boost::asio::connect(socket, endpoints); 的示例代码。要求是它应该在 5 秒而不是 15 秒内超时。

Answer 1

你看过下面的example吗？它包含一个带有超时的示例代码async_connect。

超时连接方法可以使用以下代码实现：

void connect(const std::string& host, const std::string& service,
  boost::posix_time::time_duration timeout)  {
// Resolve the host name and service to a list of endpoints.
tcp::resolver::query query(host, service);
tcp::resolver::iterator iter = tcp::resolver(io_service_).resolve(query);

// Set a deadline for the asynchronous operation. As a host name may
// resolve to multiple endpoints, this function uses the composed operation
// async_connect. The deadline applies to the entire operation, rather than
// individual connection attempts.
deadline_.expires_from_now(timeout);

// Set up the variable that receives the result of the asynchronous
// operation. The error code is set to would_block to signal that the
// operation is incomplete. Asio guarantees that its asynchronous
// operations will never fail with would_block, so any other value in
// ec indicates completion.
boost::system::error_code ec = boost::asio::error::would_block;

// Start the asynchronous operation itself. The boost::lambda function
// object is used as a callback and will update the ec variable when the
// operation completes. The blocking_udp_client.cpp example shows how you
// can use boost::bind rather than boost::lambda.
boost::asio::async_connect(socket_, iter, var(ec) = _1);

// Block until the asynchronous operation has completed.
do io_service_.run_one(); while (ec == boost::asio::error::would_block);

// Determine whether a connection was successfully established. The
// deadline actor may have had a chance to run and close our socket, even
// though the connect operation notionally succeeded. Therefore we must
// check whether the socket is still open before deciding if we succeeded
// or failed.
if (ec || !socket_.is_open())
  throw boost::system::system_error(
      ec ? ec : boost::asio::error::operation_aborted);
}