boost::asio::deadline_timer doesn't call handler

Question

I have a tcp client that polls a server for an answer with a deadline so that if the server cannot be reached the client is not blocked. The problem I have encountered is that the async_wait never seems to call its handler, effectively blocking the client when it fails to connect. Every call to tcpPoll will have its own thread (which is why I create a new io_service) but it doesn't seem to work even without multithreading. Also, the NetworkEntity object can call tcpPoll more than once during its lifetime.

My question would be : What is blocking the deadline_timer from calling its handler? (and how to fix it)

Here is some relevant code, which is working as long as nothing fails (connect, write, read) (sorry if it's a bit long) :

void NetworkEntity::stop()
{
    stopped_ = true;
    //close socket
    //cancel timeout
}

void NetworkEntity::check_timeout(const boost::system::error_code& error)
{
    if (stopped_)
        return;
    if (timeout_.expires_at() <= boost::asio::deadline_timer::traits_type::now())
    {
        stop();
        timeout_.expires_at(boost::posix_time::pos_infin);
        std::cout << address_ << " timed out\n";
    }
    timeout_.async_wait(boost::bind(&NetworkEntity::check_timeout, this, boost::asio::placeholders::error));
}

std::vector<std::string> NetworkEntity::tcpPoll(const char* message, const char endOfMessage)
{
    boost::asio::io_service io_service;
    stopped_ = false;
    timeout_.expires_from_now(boost::posix_time::seconds(TIMEOUT_));
    timeout_.async_wait(boost::bind(&NetworkEntity::check_timeout, this, boost::asio::placeholders::error));
    tcp::resolver resolver(io_service);
    start_connect(&io_service, resolver.resolve(tcp::resolver::query(address_, port_)), message, endOfMessage);
    io_service.run();
    //retrieve answer from class
    //return answer
}

void NetworkEntity::start_connect(boost::asio::io_service* io_service, tcp::resolver::iterator endpoint_iterator, const std::string message, const char endOfMessage)
{
    socket_.reset(new tcp::socket(*io_service));
    socket_->async_connect(endpoint_iterator->endpoint(),
        boost::bind(&NetworkEntity::handle_connect, this, io_service, boost::asio::placeholders::error, endpoint_iterator, message, endOfMessage));
}

void NetworkEntity::handle_connect(boost::asio::io_service* io_service, const boost::system::error_code& err, tcp::resolver::iterator endpoint_iterator, const std::string message, const char endOfMessage)
{
    if(stopped_)
        return;
    if (err)
    {
        std::cout << "Connect error: " << err.message() << "\n";
        stop();
    }
    else
    {
        start_write(message, endOfMessage);
    }
}

void NetworkEntity::start_write(const std::string message, const char endOfMessage)
{
    std::ostream request_stream(&request_);
    request_stream << message;
    boost::asio::async_write(*socket_, request_,
        boost::bind(&NetworkEntity::handle_write, this, boost::asio::placeholders::error, endOfMessage));
}

void NetworkEntity::handle_write(const boost::system::error_code& error, const char endOfMessage)
{
    if (stopped_)
        return;
    if (!error)
    {
        //sleep for 500ms to let time for the reciever to process info (had a bug on this one)
        start_read(endOfMessage);
    }
    else
    {
        std::cout << "write error : " << error.message() << "\n";
        stop();
    }
}

void NetworkEntity::start_read(const char endOfMessage)
{
    boost::asio::async_read_until(*socket_, answer_, endOfMessage,
        boost::bind(&NetworkEntity::handle_read, this, boost::asio::placeholders::error));
}

void NetworkEntity::handle_read(const boost::system::error_code& error)
{
    if (stopped_)
        return;
    if (error)
    {
        std::cout << "read error : " << error.message() << "\n";
        stop();
    }
    else
    {
        stop();
    }
}

Answer 1

I think you must be confused with multiple instances of io_service.

The reason I think this is because in your code you never show how you initialize timeout_. And the io_service instance you are using for the connection is only instantiated inside your tcpPoll function... This leads me to believe that you are accidentally registering the deadline timer on a separate io_service that you don't even run?

Here's a version that actually works, notes:

1. it has done away with the stopped_ boolean, as it's unnecessary and bound to confuse
2. see new implementation of check_timeout and stop on how to detect the various program flows
3. the full code, self-contained, is exactly only few more lines of code than what you posted in the question

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

using tcp = boost::asio::ip::tcp;

struct NetworkEntity {

    boost::asio::io_service io_service;
    boost::asio::deadline_timer timeout_{io_service};
    std::string address_ = "localhost";
    std::string port_    = "6767";
    int TIMEOUT_         = 3;
    boost::shared_ptr<tcp::socket> socket_;
    boost::asio::streambuf request_, answer_;

    void stop()
    {
        if (socket_)
        {
            socket_->cancel();
            socket_->close();
        }
        timeout_.cancel();
        io_service.stop();
    }

    void check_timeout(const boost::system::error_code& error)
    {
        if (error != boost::asio::error::operation_aborted)
        {
            stop();
            std::cout << address_ << " timed out\n";
        }
        timeout_.async_wait(boost::bind(&NetworkEntity::check_timeout, this, boost::asio::placeholders::error));
    }

    std::vector<std::string> tcpPoll(const char* message, const char endOfMessage)
    {
        timeout_.expires_from_now(boost::posix_time::seconds(TIMEOUT_));
        timeout_.async_wait(boost::bind(&NetworkEntity::check_timeout, this, boost::asio::placeholders::error));

        tcp::resolver resolver(io_service);
        start_connect(&io_service, resolver.resolve(tcp::resolver::query(address_, port_)), message, endOfMessage);

        io_service.run();
        //retrieve answer from class
        //return answer
        std::ostringstream oss;
        oss << &answer_;
        return { oss.str() };
    }

    void start_connect(boost::asio::io_service* io_service, tcp::resolver::iterator endpoint_iterator, const std::string message, const char endOfMessage)
    {
        socket_.reset(new tcp::socket(*io_service));
        socket_->async_connect(endpoint_iterator->endpoint(),
                boost::bind(&NetworkEntity::handle_connect, this, io_service, boost::asio::placeholders::error, endpoint_iterator, message, endOfMessage));
    }

    void handle_connect(boost::asio::io_service* io_service,
            const boost::system::error_code& err,
            tcp::resolver::iterator endpoint_iterator,
            const std::string message,
            const char endOfMessage)
    {
        if (err)
        {
            std::cout << "Connect error: " << err.message() << "\n";
            stop();
        }
        else
        {
            start_write(message, endOfMessage);
        }
    }

    void start_write(const std::string message, const char endOfMessage)
    {
        std::ostream request_stream(&request_);
        request_stream << message;
        boost::asio::async_write(*socket_, request_,
                boost::bind(&NetworkEntity::handle_write, this, boost::asio::placeholders::error, endOfMessage));
    }

    void handle_write(const boost::system::error_code& error, const char endOfMessage)
    {
        if (!error)
        {
            //sleep for 500ms to let time for the reciever to process info (had a bug on this one)
            start_read(endOfMessage);
        }
        else
        {
            std::cout << "write error : " << error.message() << "\n";
            stop();
        }
    }

    void start_read(const char endOfMessage)
    {
        boost::asio::async_read_until(*socket_, answer_, endOfMessage,
                boost::bind(&NetworkEntity::handle_read, this, boost::asio::placeholders::error));
    }

    void handle_read(const boost::system::error_code& error)
    {
        if (error)
        {
            std::cout << "read error : " << error.message() << "\n";
        }
        stop();
    }
};

int main()
{
    NetworkEntity ne;
    for (auto& s : ne.tcpPoll("this is my request", '\n'))
    {
        std::cout << "Line: '" << s << "'\n";
    }
}