test(emqx_broker_SUITE): fix flaky test case

apps/emqx/src/emqx_cm.erl

@@ -721,8 +721,8 @@ do_get_chann_conn_mod(ClientId, ChanPid) ->
     end.
 
 mark_channel_connected(ChanPid) ->
-    ?tp(emqx_cm_connected_client_count_inc, #{chan_pid => ChanPid}),
     ets:insert_new(?CHAN_LIVE_TAB, {ChanPid, true}),
+    ?tp(emqx_cm_connected_client_count_inc, #{chan_pid => ChanPid}),
     ok.
 
 mark_channel_disconnected(ChanPid) ->

apps/emqx/test/emqx_broker_SUITE.erl

@@ -559,45 +559,70 @@ t_connected_client_count_transient_takeover(Config) when is_list(Config) ->
     %% we spawn several clients simultaneously to cause the race
     %% condition for the client id lock
     NumClients = 20,
+    ConnectSuccessCntr = counters:new(1, []),
+    ConnectFailCntr = counters:new(1, []),
+    ConnectFun =
+        fun() ->
+            process_flag(trap_exit, true),
+            try
+                {ok, ConnPid} =
+                    emqtt:start_link([
+                        {clean_start, true},
+                        {clientid, ClientID}
+                        | Config
+                    ]),
+                {ok, _} = emqtt:ConnFun(ConnPid),
+                counters:add(ConnectSuccessCntr, 1, 1)
+            catch
+                _:_ ->
+                    counters:add(ConnectFailCntr, 1, 1)
+            end
+        end,
     {ok, {ok, [_, _]}} =
         wait_for_events(
             fun() ->
                 lists:foreach(
                     fun(_) ->
-                        spawn(
-                            fun() ->
-                                {ok, ConnPid} =
-                                    emqtt:start_link([
-                                        {clean_start, true},
-                                        {clientid, ClientID}
-                                        | Config
-                                    ]),
-                                %% don't assert the result: most of them fail
-                                %% during the race
-                                emqtt:ConnFun(ConnPid),
-                                ok
-                            end
-                        ),
-                        ok
+                        spawn(ConnectFun)
                     end,
                     lists:seq(1, NumClients)
-                )
+                ),
+                ok
             end,
-            %% there can be only one channel that wins the race for the
-            %% lock for this client id.  we also expect a decrement
-            %% event because the client dies along with the ephemeral
-            %% process.
+            %% At least one channel acquires the lock for this client id.  We
+            %% also expect a decrement event because the client dies along with
+            %% the ephemeral process.
             [
                 emqx_cm_connected_client_count_inc,
-                emqx_cm_connected_client_count_dec
+                emqx_cm_connected_client_count_dec_done
             ],
-            1000
+            _Timeout = 10000
         ),
     %% Since more than one pair of inc/dec may be emitted, we need to
     %% wait for full stabilization
-    timer:sleep(100),
-    %% It must be 0 again because we spawn-linked the clients in
-    %% ephemeral processes above, and all should be dead now.
+    ?retry(
+        _Sleep = 100,
+        _Retries = 100,
+        begin
+            ConnectSuccessCnt = counters:get(ConnectSuccessCntr, 1),
+            ConnectFailCnt = counters:get(ConnectFailCntr, 1),
+            NumClients = ConnectSuccessCnt + ConnectFailCnt
+        end
+    ),
+    ConnectSuccessCnt = counters:get(ConnectSuccessCntr, 1),
+    ?assert(ConnectSuccessCnt > 0),
+    EventsThatShouldHaveHappened = lists:flatten(
+        lists:duplicate(
+            ConnectSuccessCnt,
+            [
+                emqx_cm_connected_client_count_inc,
+                emqx_cm_connected_client_count_dec_done
+            ]
+        )
+    ),
+    wait_for_events(fun() -> ok end, EventsThatShouldHaveHappened, 10000, infinity),
+    %% It must be 0 again because we got enough
+    %% emqx_cm_connected_client_count_dec_done events
     ?assertEqual(0, emqx_cm:get_connected_client_count()),
     %% connecting again
     {ok, ConnPid1} = emqtt:start_link([
@@ -608,7 +633,8 @@ t_connected_client_count_transient_takeover(Config) when is_list(Config) ->
     {{ok, _}, {ok, [_]}} =
         wait_for_events(
             fun() -> emqtt:ConnFun(ConnPid1) end,
-            [emqx_cm_connected_client_count_inc]
+            [emqx_cm_connected_client_count_inc],
+            _Timeout = 10000
         ),
     ?assertEqual(1, emqx_cm:get_connected_client_count()),
     %% abnormal exit of channel process
@@ -620,9 +646,10 @@ t_connected_client_count_transient_takeover(Config) when is_list(Config) ->
                 ok
             end,
             [
-                emqx_cm_connected_client_count_dec,
+                emqx_cm_connected_client_count_dec_done,
                 emqx_cm_process_down
-            ]
+            ],
+            _Timeout = 10000
         ),
     ?assertEqual(0, emqx_cm:get_connected_client_count()),
     ok;
@@ -735,11 +762,14 @@ wait_for_events(Action, Kinds) ->
     wait_for_events(Action, Kinds, 500).
 
 wait_for_events(Action, Kinds, Timeout) ->
+    wait_for_events(Action, Kinds, Timeout, 0).
+
+wait_for_events(Action, Kinds, Timeout, BackInTime) ->
     Predicate = fun(#{?snk_kind := K}) ->
         lists:member(K, Kinds)
     end,
     N = length(Kinds),
-    {ok, Sub} = snabbkaffe_collector:subscribe(Predicate, N, Timeout, 0),
+    {ok, Sub} = snabbkaffe_collector:subscribe(Predicate, N, Timeout, BackInTime),
     Res = Action(),
     case snabbkaffe_collector:receive_events(Sub) of
         {timeout, _} ->