how to handle control-c in a boost tcp/udp server

Question

How do I handle the control-C event or stop my boost::asio server. I have a tcp & udp combined server and would like to be able to exit cleanly when I press ctrl-c. I get a first chance exception for unhandled control-C. Here is my code

void startTCP()
{
  http::syncServer::server serv( 2);

 // Set console control handler to allow server to be stopped.
 // console_ctrl_function = boost::bind(&http::syncServer::server::stop, &serv);
 //SetConsoleCtrlHandler(console_ctrl_handler, TRUE);
 // Run the server until stopped.
 serv.run();
}


void startUDP()
{
  boost::asio::io_service io_service;
  http::syncServer::udp_server server(io_service);
 // console_ctrl_function = boost::bind(&http::syncServer::udp_server::stop, &server);
 // SetConsoleCtrlHandler(console_ctrl_handler, TRUE);
 io_service.run();
}

int main(int argc, char* argv[])
{
  try
  {
     boost::shared_ptr<boost::thread> tcpThread( new boost::thread(startTCP));
     boost::shared_ptr<boost::thread> udpThread (new boost::thread(startUDP));

     /*console_ctrl_function = boost::bind(&http::syncServer::udp_server::stop, &server);
     SetConsoleCtrlHandler(console_ctrl_handler, FALSE);*/

    tcpThread->join();
    udpThread->join();
}
catch (std::exception& e)
{
   std::cerr << "exception: " << e.what() << "\n";
}

return 0;
}

Answer 1

As of boost 1.47 you can use signal_set from asio:

class Server {
public:
  Server(...) {
    _signals.add(SIGINT);
    _signals.add(SIGTERM);
    _signals.async_wait(bind(&Server::handle_stop, this));

  }
  void handle_stop() {
    // do what you need to kill the Server - usually you just have to cancel all waits (incl deadline_timers), which will make the io_service exit gracefully
  }
private:
  boost::asio::signal_set _signals;
};

Beware, boost versions of e.g. latest Ubuntu is 1.46 - so this is bleeding edge (primo 2012).

Cheers,

Michael

Answer 2

The C standard library contains <signal.h> (e.g. see here), with which you can register a signal handler for SIGINT (Ctrl-C). That should do the trick, supposing your platform supports signals.

You might also want to register a handler for SIGTERM to respond gracefully to being kill(1)ed.

#include <signal.h> // or <csignal> in C++

void ctrlchandler(int) { /*...*/ WE_MUST_STOP = 1; }
void killhandler(int) { /*...*/ WE_MUST_STOP = 2; }

int WE_MUST_STOP = 0;

int main() {
  signal(SIGINT, ctrlchandler);
  signal(SIGTERM, killhandler);
  /* ... */

  // e.g. main loop like this:
  while(pump_loop() && 0 == WE_MUST_STOP) { }

}

---

As suggested by Sam Miller, suppose your main loop is a single-threaded boost.asio loop with some m_io_service.run(). Then instead of the global flags you could (assuming m_io_service is visible) post a stop handler to the io service from within the signal handlers.