+After retrieving the board, the function adds a new waiter to the
+current list of waiters and returns without sending a reply.
+
+Before returning, it increases the reference count of the
+request **req** using the function **afb_req_addref**.
+
+> When the implentation of a verb returns without sending a reply,
+> it **MUST** increment the reference count of the request
+> using **afb_req_addref**. If it doesn't bad things can happen.
+
+Later, when the board changes, it calls the function **changed**
+of *tic-tac-toe* with the reason of the change.
+
+Here is the full listing of the function **changed**:
+
+ /*
+ * signals a change of the board
+ */
+ static void changed(struct board *board, const char *reason)
+ {
+ struct waiter *waiter, *next;
+ struct json_object *description;
+
+ /* get the description */
+ description = describe(board);
+
+ waiter = board->waiters;
+ board->waiters = NULL;
+ while (waiter != NULL) {
+ next = waiter->next;
+ afb_req_success(waiter->req, json_object_get(description), reason);
+ afb_req_unref(waiter->req);
+ free(waiter);
+ waiter = next;
+ }
+
+ afb_event_sender_push(afb_daemon_get_event_sender(afbitf->daemon), reason, description);
+ }
+
+The list of waiters is walked and a reply is sent to each waiter.
+After the sending the reply, the reference count of the request
+is decremented using **afb_req_unref** to allow its resources to be freed.
+
+> The reference count **MUST** be decremented using **afb_req_unref** because,
+> otherwise, there is a leak of resources.
+> It must be decremented **AFTER** the sending of the reply, because, otherwise,
+> bad things may happen.