C++ boost::asio::ip::tcp::acceptor sometimes doesn't accept connector?

Question

I currently have a very weird problem. Sometimes my ::acceptor (using async_accept) doesn't accept a socket (there is no call of the accept function specified in async_accept) but the connector returns true on the connect function (both boost::asio:: classes). Sometimes all works but sometimes I don't get an acceptor socket.... I really don't know why anymore. I tested everything under Win10 64bit with different listen_ports.
My server structure is the following:
io_service:

_io_thread = std::make_unique<std::thread>([this]() {
            while (1)
            {
                try
                {
                    _io_service->run();
                    break;
                }
                catch (const boost::exception& e)
                {
                    spdlog::error("IO_SERVICE_EXCEPTION: ", boost::diagnostic_information(e));
                }
            }
        });

acceptor:

void Server::initialize(uint16_t listen_port)
    {
        // at this point the io_thread is running already

        auto endpoint = ip::tcp::endpoint(ip::tcp::v4(), listen_port);

        _acceptor = std::make_unique<boost::asio::ip::tcp::acceptor>(*_io_service, endpoint.protocol());
        _acceptor->set_option(boost::asio::ip::tcp::acceptor::reuse_address(false));
        _acceptor->bind(endpoint);
        _acceptor->listen();

        _listen_port = listen_port;

        __accept();
    }

__accept():

void Server::__accept()
    {
        // create socket for next connection
        _acceptor_socket = std::make_unique<ip::tcp::socket>(*_io_service);

        _acceptor->async_accept(*_acceptor_socket, [this](const boost::system::error_code& err)
            {
                spdlog::info("Accept new socket..."); // this sometimes doesn't get called :(

                if (err.failed())
                {
                    // acceptor closed
                    if (err == boost::asio::error::operation_aborted)
                    {
                        spdlog::info("network server stopped accepting sockets");
                        return;
                    }

                    // unknown error
                    spdlog::error("network server accepting socket failed {} message {} num {}", err.failed(), err.message(), err.value());

                    // accept next connection
                    __accept();
                    return;
                }

                // accept new socket
                _new_connections_mutex.lock();

                auto con = __create_new_connection();
                con->initialize(++_connection_id_counter, std::move(_acceptor_socket));
                con->set_handler(_input_handler);
                con->goto_phase(_initial_phase);
                spdlog::info("new connection from {} with id {}", con->get_host_name(), con->get_unique_id());

                _new_connections[con->get_unique_id()] = std::move(con);

                _new_connections_mutex.unlock();

                // wait for next connection
                __accept();
            }
        );
    }

My client connector is simple like that:

        auto socket = std::make_unique<boost::asio::ip::tcp::socket>(*_io_service);

        spdlog::info("try to connect to {}:{}", endpoint.address().to_string(), endpoint.port());
        try
        {
            socket->connect(endpoint);
        }
        catch (const boost::system::system_error & e)
        {
            spdlog::error("cannot connect to {}:{}", endpoint.address().to_string(), endpoint.port());
            return false;
        }

        // this succeeds everytime...
        [...]

So... shouldn't everytime when the connector socket succeeds to connect the acceptor socket be created as well? I hope somebody knows what's going wrong here :/

Answer 1

Okay I found the answer.... the io_service::run function doesn't work as I expected. I thought it will just block forever if io_service::stop is not called. Seems like that is wrong. Because I break after one ::run call out of my while loop and then the thread is finished the io_service sometimes didn't run anymore when the connector socket connected. Have changed the io_service::run -> run_one() and removed the break. Will now add a loop-cancel variable so it's no infinite loop...
Thanks for your answers !