fix: restart emqx_statsd with the updated configuration

emqx_config_handler:post_config_update/5 cb is called before an updated config is saved.
Thus, a process being restarted in that callback cannot get the latest config by calling
emqx_conf:get/2, because that update is not saved yet.

Relates to EMQX-9055

apps/emqx_statsd/src/emqx_statsd.erl

@@ -38,7 +38,7 @@
 ]).
 
 %% Interface
--export([start_link/0]).
+-export([start_link/1]).
 
 %% Internal Exports
 -export([
@@ -68,17 +68,17 @@ do_restart() ->
     ok = do_start(),
     ok.
 
-start_link() ->
+start_link(Conf) ->
-    gen_server:start_link({local, ?MODULE}, ?MODULE, [], []).
+    gen_server:start_link({local, ?MODULE}, ?MODULE, Conf, []).
 
-init([]) ->
+init(Conf) ->
     process_flag(trap_exit, true),
     #{
         tags := TagsRaw,
         server := Server,
         sample_time_interval := SampleTimeInterval,
         flush_time_interval := FlushTimeInterval
-    } = emqx_conf:get([statsd]),
+    } = Conf,
     {Host, Port} = emqx_schema:parse_server(Server, ?SERVER_PARSE_OPTS),
     Tags = maps:fold(fun(K, V, Acc) -> [{to_bin(K), to_bin(V)} | Acc] end, [], TagsRaw),
     Opts = [{tags, Tags}, {host, Host}, {port, Port}, {prefix, <<"emqx">>}],

apps/emqx_statsd/src/emqx_statsd_config.erl

@@ -45,9 +45,9 @@ remove_handler() ->
     ok = emqx_config_handler:remove_handler(?STATSD),
     ok.
 
-post_config_update(?STATSD, _Req, #{enable := true}, _Old, _AppEnvs) ->
+post_config_update(?STATSD, _Req, #{enable := true} = New, _Old, _AppEnvs) ->
     emqx_statsd_sup:ensure_child_stopped(?APP),
-    emqx_statsd_sup:ensure_child_started(?APP);
+    emqx_statsd_sup:ensure_child_started(?APP, New);
 post_config_update(?STATSD, _Req, #{enable := false}, _Old, _AppEnvs) ->
     emqx_statsd_sup:ensure_child_stopped(?APP);
 post_config_update(_ConfPath, _Req, _NewConf, _OldConf, _AppEnvs) ->

apps/emqx_statsd/src/emqx_statsd_sup.erl

@@ -25,6 +25,7 @@
 -export([
     start_link/0,
     ensure_child_started/1,
+    ensure_child_started/2,
     ensure_child_stopped/1
 ]).
 
@@ -45,7 +46,11 @@ start_link() ->
 
 -spec ensure_child_started(atom()) -> ok.
 ensure_child_started(Mod) when is_atom(Mod) ->
-    assert_started(supervisor:start_child(?MODULE, ?CHILD(Mod, []))).
+    ensure_child_started(Mod, emqx_conf:get([statsd], #{})).
+
+-spec ensure_child_started(atom(), map()) -> ok.
+ensure_child_started(Mod, Conf) when is_atom(Mod) ->
+    assert_started(supervisor:start_child(?MODULE, ?CHILD(Mod, [Conf]))).
 
 %% @doc Stop the child worker process.
 -spec ensure_child_stopped(any()) -> ok.
@@ -61,9 +66,9 @@ ensure_child_stopped(ChildId) ->
 
 init([]) ->
     Children =
-        case emqx_conf:get([statsd, enable], false) of
+        case emqx_conf:get([statsd], #{}) of
-            true -> [?CHILD(emqx_statsd, [])];
+            #{enable := true} = Conf -> [?CHILD(emqx_statsd, [Conf])];
-            false -> []
+            _ -> []
         end,
     {ok, {{one_for_one, 100, 3600}, Children}}.
 

apps/emqx_statsd/test/emqx_statsd_SUITE.erl

@@ -113,6 +113,32 @@ t_kill_exit(_) ->
     ?assertNotEqual(Estatsd, Estatsd1),
     ok.
 
+t_config_update(_) ->
+    OldRawConf = emqx_conf:get_raw([statsd]),
+    {ok, _} = emqx_statsd_config:update(OldRawConf#{<<"enable">> => true}),
+    CommonKeys = [flush_time_interval, sample_time_interval],
+    OldConf = emqx_conf:get([statsd]),
+    OldStatsDState = sys:get_state(emqx_statsd),
+    OldPid = erlang:whereis(emqx_statsd),
+    ?assertEqual(maps:with(CommonKeys, OldConf), maps:with(CommonKeys, OldStatsDState)),
+    NewRawConfExpect = OldRawConf#{
+        <<"flush_time_interval">> := <<"42s">>,
+        <<"sample_time_interval">> := <<"42s">>
+    },
+    try
+        {ok, _} = emqx_statsd_config:update(NewRawConfExpect),
+        NewRawConf = emqx_conf:get_raw([statsd]),
+        NewConf = emqx_conf:get([statsd]),
+        NewStatsDState = sys:get_state(emqx_statsd),
+        NewPid = erlang:whereis(emqx_statsd),
+        ?assertNotEqual(OldRawConf, NewRawConf),
+        ?assertEqual(NewRawConfExpect, NewRawConf),
+        ?assertEqual(maps:with(CommonKeys, NewConf), maps:with(CommonKeys, NewStatsDState)),
+        ?assertNotEqual(OldPid, NewPid)
+    after
+        {ok, _} = emqx_statsd_config:update(OldRawConf)
+    end.
+
 request(Method) -> request(Method, []).
 
 request(Method, Body) ->