server: Add a mutex to kill a very small, bad race

irc/server.go

@@ -68,6 +68,7 @@ type Server struct {
 	store                 buntdb.DB
 	idle                  chan *Client
 	limits                Limits
+	listenerEventActMutex sync.Mutex
 	listenerUpdateMutex   sync.Mutex
 	listeners             map[string]ListenerInterface
 	monitoring            map[string][]Client
@@ -341,6 +342,11 @@ func (s *Server) createListener(addr string, tlsMap map[string]*tls.Config) {
 
 			select {
 			case event := <-s.listeners[addr].Events:
+				// this is used to confirm that whoever passed us this event has closed the existing listener correctly (in an attempt to get us to notice the event).
+				// this is required to keep REHASH from having a very small race possibility of killing the primary listener
+				s.listenerEventActMutex.Lock()
+				s.listenerEventActMutex.Unlock()
+
 				if event.Type == DestroyListener {
 					// listener should already be closed, this is just for safety
 					listener.Close()
@@ -922,6 +928,7 @@ func rehashHandler(server *Server, client *Client, msg ircmsg.IrcMessage) bool {
 			}
 		}
 
+		server.listenerEventActMutex.Lock()
 		if exists {
 			// update old listener
 			fmt.Println("refreshing", addr)
@@ -938,6 +945,8 @@ func rehashHandler(server *Server, client *Client, msg ircmsg.IrcMessage) bool {
 		}
 		// force listener to apply the event right away
 		server.listeners[addr].Listener.Close()
+
+		server.listenerEventActMutex.Unlock()
 	}
 
 	for _, newaddr := range config.Server.Listen {