服务器关闭并重新启动后，客户端无法连接

Question

I have a problem with my C++ networking code(a test server that receives strings and displays it). Occasionally, when I turn off my server(Ctrl C) and then restart it, clients fail to connect to it. If I wait for around a minute and try connecting with a client again, it works perfect. Doing a ps -A | grep my_server ps -A | grep my_server I don't find the process running. However, if I'd try to connect in about 2 minutes it would work just fine.

I find this rather strange.

I'm used to a slightly similar problem in Python, where I have trouble connecting to a port after pressing Ctrl+C. In that case, the process might still be running and I'd have to manually kill the process and try connecting again(and it would work just fine then).

Is there any code that you'd like me to paste in particular? I'm accepting the connections as follows :-

NetworkManager* start_listening(char* host, int port) {
  keep_running = true;
  signal(SIGINT, signal_handler);
  int listenfd, connfd, n;
  struct sockaddr_in servaddr, cliaddr;
  socklen_t clilen;
  pid_t pid;

  listenfd = socket(AF_INET, SOCK_STREAM, 0);

  bzero(&servaddr, sizeof(servaddr));
  servaddr.sin_family = AF_INET;
  servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
  servaddr.sin_port = htons(port);
#ifdef DEBUG
  std::cout << "[+] Starting to listen at port " << port << std::endl;
#endif
#ifdef DEBUG
  std::cout << "[+] Binding to port" << std::endl;
#endif
  bind(listenfd, (struct sockaddr *)&servaddr, sizeof(servaddr));

#ifdef DEBUG
  std::cout << "[+] Starting to listen" << std::endl;
#endif
  listen(listenfd, 1024);
  clilen = sizeof(cliaddr);

  while ( keep_running ) {
    connfd = accept(listenfd, (struct sockaddr *)&cliaddr, &clilen);
#ifdef DEBUG
    if ( connfd == -1 ) {
      std::cout << "Yikes got an error with errno = " << errno << std::endl;
    }
    sockaddr_in* pV4Addr = (struct sockaddr_in*)&cliaddr;
    int ipAddr = pV4Addr->sin_addr.s_addr;
    char str[20];
    inet_ntop(AF_INET, &ipAddr, str, 20);
    std::cout << "[+] Incoming connection from " << str << std::endl;
    std::cout << "[+] Using socket " << connfd << std::endl;
#endif

    if ( (pid=fork()) == 0 ) {
      close(listenfd);
      NetworkManager *nm = new NetworkManager(connfd);
      return nm;
    } else {
      close(connfd);
    }
  }

  if (!keep_running) {
    // #TODO kill all children
#ifdef DEBUG
    std::cout << "[+] Killing server" << std::endl;
#endif
    exit(0);
  }
  return 0;
}

Answer 1

The problem is that you're not checking your return values. For example, to bind. Which could be failing. For example, because you aren't using REUSEADDR to allow binding to a port which was recently in use. There's a timeout on these things, and that was a dead giveaway when you mentioned that it works again after two minutes. But really, check your return values--this is C after all!