Prevent duplicate room creation.

src/app/spreed-speakfreely-server/hub.go

@@ -161,6 +161,10 @@ func (h *Hub) GetRoom(id string) *RoomWorker {
 	if !ok {
 		h.mutex.RUnlock()
 		h.mutex.Lock()
+		// need to re-check, another thread might have created the room
+		// while we waited for the lock
+		room, ok = h.roomTable[id]
+		if !ok {
 			room = NewRoomWorker(h, id)
 			h.roomTable[id] = room
 			h.mutex.Unlock()
@@ -173,6 +177,9 @@ func (h *Hub) GetRoom(id string) *RoomWorker {
 				delete(h.roomTable, id)
 				log.Printf("Cleaned up room '%s'\n", id)
 			}()
+		} else {
+			h.mutex.Unlock()
+		}
 	} else {
 		h.mutex.RUnlock()
 	}