diff --git a/src/emqttd_cm.erl b/src/emqttd_cm.erl
index 34a130508..f78db2ad0 100644
--- a/src/emqttd_cm.erl
+++ b/src/emqttd_cm.erl
@@ -70,14 +70,14 @@ lookup_proc(ClientId) when is_binary(ClientId) ->
 %% @doc Register ClientId with Pid.
 -spec(register(Client :: mqtt_client()) -> ok).
 register(Client = #mqtt_client{client_id = ClientId}) ->
-    CmPid = gproc_pool:pick_worker(?POOL, ClientId),
-    gen_server2:cast(CmPid, {register, Client}).
+    gen_server2:call(pick(ClientId), {register, Client}, 120000).
 
 %% @doc Unregister clientId with pid.
 -spec(unregister(ClientId :: binary()) -> ok).
 unregister(ClientId) when is_binary(ClientId) ->
-    CmPid = gproc_pool:pick_worker(?POOL, ClientId),
-    gen_server2:cast(CmPid, {unregister, ClientId, self()}).
+    gen_server2:cast(pick(ClientId), {unregister, ClientId, self()}).
+
+pick(ClientId) -> gproc_pool:pick_worker(?POOL, ClientId).
 
 %%--------------------------------------------------------------------
 %% gen_server callbacks
@@ -85,16 +85,16 @@ unregister(ClientId) when is_binary(ClientId) ->
 
 init([Pool, Id, StatsFun]) ->
     ?GPROC_POOL(join, Pool, Id),
-    {ok, #state{pool = Pool, id = Id,
-                statsfun = StatsFun,
-                monitors = dict:new()}}.
+    {ok, #state{pool = Pool, id = Id, statsfun = StatsFun, monitors = dict:new()}}.
 
-prioritise_call(_Req, _From, _Len, _State) ->
-    1.
+prioritise_call(Req, _From, _Len, _State) ->
+    case Req of
+        {register,   _Client} -> 2;
+        _                     -> 1
+    end.
 
 prioritise_cast(Msg, _Len, _State) ->
     case Msg of
-        {register,   _Client}         -> 2;
         {unregister, _ClientId, _Pid} -> 9;
         _                             -> 1
     end.
@@ -102,19 +102,19 @@ prioritise_cast(Msg, _Len, _State) ->
 prioritise_info(_Msg, _Len, _State) ->
     3.
 
-handle_call(Req, _From, State) ->
-    ?UNEXPECTED_REQ(Req, State).
-
-handle_cast({register, Client = #mqtt_client{client_id  = ClientId,
-                                             client_pid = Pid}}, State) ->
+handle_call({register, Client = #mqtt_client{client_id  = ClientId,
+                                             client_pid = Pid}}, _From, State) ->
     case lookup_proc(ClientId) of
         Pid ->
-            {noreply, State};
+            {reply, ok, State};
         _ ->
             ets:insert(mqtt_client, Client),
-            {noreply, setstats(monitor_client(ClientId, Pid, State))}
+            {reply, ok, setstats(monitor_client(ClientId, Pid, State))}
     end;
 
+handle_call(Req, _From, State) ->
+    ?UNEXPECTED_REQ(Req, State).
+
 handle_cast({unregister, ClientId, Pid}, State) ->
     case lookup_proc(ClientId) of
         Pid ->