boost::acceptor::cancel doesn't work as expected

Question

I've implemented a SocketServer using boost. This SocketServer is intended to work as follow:

• accept connections for a certain amount of time
• stop handling sockets after timeout is reached

Here is my code:

ServerSocket::ServerSocket(unsigned int port)
{
    _io_service.reset(new boost::asio::io_service()) ;
    _endpoint.reset(new boost::asio::ip::tcp::endpoint(boost::asio::ip::tcp::v4(), port));
    _acceptor.reset(new boost::asio::ip::tcp::acceptor(*_io_service, *_endpoint)) ;
    _newConnection = false; 
}

bool ServerSocket::accept(boost::asio::ip::tcp::socket& socket, int timeout)
{
    _newConnection = false;
    _acceptor->async_accept(socket, boost::bind(&ServerSocket::handleAccept, this, &socket));
    _io_service->reset();

    if (timeout > 0)
    {
        int incrementation = 1;
        int time_spent = 0;
        while (time_spent < timeout && !_io_service->poll_one())
        {
            time_spent += incrementation;
            sleep(incrementation);
        }
    }
    else
    {
        _io_service->run_one();
    }

    if (!_newConnection)
    {
        _acceptor->cancel();
    }

    return _newConnection;

}

void ServerSocket::handleAccept(boost::asio::ip::tcp::socket* pSocket)
{
    _newConnection = true;
};

My problem is the following: when I call accept() with a timeout and a socket A. If the timeout is reached and I call it again with a new socket B, if then the accept() works, I handle A instead of B.

Tell me if there are information missing.

Answer 1

You can simply use the io_service's task loop, and use a deadline timer to cancel the operation on the acceptor.

Live On Coliru

#include <boost/asio.hpp>
#include <boost/bind.hpp>

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

struct ServerSocket
{
    asio::io_service _io_service;
    tcp::endpoint _endpoint;
    tcp::acceptor _acceptor;
    asio::deadline_timer _timer;
    bool _newConnection;

    ServerSocket(unsigned int port)
        : _io_service(),
          _endpoint(tcp::v4(), port),
          _acceptor(_io_service, _endpoint),
          _timer(_io_service),
          _newConnection(false)
    {
    }

    void timer_expired(boost::system::error_code ec)
    {
        if (!ec)
        {
            _acceptor.cancel();
        }
    }

    bool accept(boost::asio::ip::tcp::socket& socket, int timeout)
    {
        _newConnection = false;
        _io_service.reset();
        _timer.expires_from_now(boost::posix_time::seconds(timeout));
        _timer.async_wait(boost::bind(&ServerSocket::timer_expired, this, asio::placeholders::error));
        _acceptor.async_accept(socket, boost::bind(&ServerSocket::handleAccept, this, &socket, asio::placeholders::error));

        _io_service.run();

        return _newConnection;
    }

    void handleAccept(boost::asio::ip::tcp::socket* pSocket, boost::system::error_code ec)
    {
        if (!ec)
        {
            _timer.cancel();
            _newConnection = true;
        }
    };
};

int main()
{
    ServerSocket s(6767);

    tcp::socket socket(s._io_service);

    if (s.accept(socket, 3))
        std::cout << "Accepted connection from " << socket.remote_endpoint() << "\n";
    else
        std::cout << "Timeout expired\n";
}

You should probably explicitly check the operation_canceled error code instead if just doing !ec but I'll leave that as an exercise for the reader.