用asio的定時器實現帶超時的connect，備忘

// test.cpp : 定義控制檯應用程序的入口點。
//

#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;
}