设置boost socket.connect的超时时间

Question

我在tcp::socket上使用boost::asio::connect。当一切正常时，connect立即返回，但在不良网络上，connect在日志等待15秒后超时。我不能等那么长时间，所以想减少超时时间。不幸的是，到目前为止我还没有找到任何解决方案。

我看到async_wait与deadline_timer一起使用的解决方案，但所有这些例子都是用于接收/发送操作，而不是用于连接。

谁能帮助我与boost::asio::connect(socket, endpoints);的样本代码。要求是它应该在5秒内超时，而不是15秒。

Answer 1

看了下面的例子吗?它包含一个示例代码async_connect与超时。

连接超时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);
}

Answer 2

我知道已经有一个公认的答案了。我发现了另一个解决方案，可能对其他人有用:

boost::asio::io_service ios;
boost::asio::ip::tcp::endpoint endpoint(remoteAddress);
boost::asio::ip::tcp::socket socket(ios);
boost::system::error_code ec;
auto connectFuture=std::async(std::launch::async,
        [this, &socket, &endpoint]() {
            boost::system::error_code connectEc;
            socket.connect(endpoint, connectEc);
    });
auto timeoutResult=connectFuture.wait_for(std::chrono::milliseconds{timeout});
if( timeoutResult==std::future_status::timeout ) {
 // timeout occured
}