用asio的定时器实现带超时的connect，备忘

// test.cpp : 定义控制台应用程序的入口点。
//

#include "stdafx.h"
#include <boost/asio.hpp>
#include <boost/bind.hpp>
#include <boost/date_time/posix_time/posix_time_types.hpp>
#include <iostream>

using namespace boost::asio;
using boost::asio::ip::tcp;

class connect_handler
{
public:
    connect_handler(io_service& ios)
        : io_service_(ios),
        timer_(ios),
        socket_(ios)
    {
        socket_.async_connect(
            tcp::endpoint(boost::asio::ip::address_v4::loopback(), 3212),
            boost::bind(&connect_handler::handle_connect, this,
            boost::asio::placeholders::error));

        timer_.expires_from_now(boost::posix_time::seconds(5));
        timer_.async_wait(boost::bind(&connect_handler::close, this));
    }

    void handle_connect(const boost::system::error_code& err)
    {
        if (err)
        {
            std::cout << "Connect error: " << err.message() << "\n";
        }
        else
        {
            std::cout << "Successful connection\n";
        }
    }

    void close()
    {
        socket_.close();
    }

private:
    io_service& io_service_;
    deadline_timer timer_;
    tcp::socket socket_;
};

int main()
{
    try
    {
        io_service ios;
        tcp::acceptor a(ios, tcp::endpoint(tcp::v4(), 32123), 1);

        // Make lots of connections so that at least some of them will block.
        connect_handler ch1(ios);
        //connect_handler ch2(ios);
        //connect_handler ch3(ios);
        //connect_handler ch4(ios);
        //connect_handler ch5(ios);
        //connect_handler ch6(ios);
        //connect_handler ch7(ios);
        //connect_handler ch8(ios);
        //connect_handler ch9(ios);

        ios.run();
    }
    catch (std::exception& e)
    {
        std::cerr << "Exception: " << e.what() << "\n";
    }

    return 0;
}