Is it possible to unlisten on a socket?

Question

Is it possible to unlisten on a socket after you have called listen(fd, backlog)?

Edit: My mistake for not making myself clear. I'd like to be able to temporarily unlisten on the socket. Calling close() will leave the socket in the M2LS state and prevent me from reopening it (or worse, some nefarious program could bind to that socket)

Temporarily unlistening would be a way (maybe not the best way) to signal to an upstream load balancer that this app couldn't accept any more requests for the moment

Answer 1

After closing the socket, your programs may still tell you that the socket is "in use", this is because of some weirdiness I don't know exactly about. But the manpage about sockets shows you there is a flag to re-use the same socket, lazily called: "SO_REUSEADDR". Set it using "setsockopt()".

Answer 2

Some socket libraries allow you to specifically reject incoming connections. For example: GNU's CommonC++: TCPsocket Class has a reject method.

BSD Sockets doesn't have this functionality. You can accept the connection and then immediately close it, while leaving the socket open:

while (running) {

  int i32ConnectFD = accept(i32SocketFD, NULL, NULL);
  while (noConnectionsPlease) {
    shutdown(i32ConnectFD, 2);
    close(i32ConnectFD);
    break;
  }

}