Optimize the emqx_zone module using persistent_term

- Don't reload the zone options for updating persistent_term is
expensive
- Use '{?MODULE, Zone, Key}' as the key to avoid name collision

src/emqx_zone.erl

@@ -41,8 +41,12 @@
         , code_change/3
         ]).
 
+%% dummy state
+-record(state, {}).
+
 -define(TAB, ?MODULE).
 -define(SERVER, ?MODULE).
+-define(KEY(Zone, Key), {?MODULE, Zone, Key}).
 
 %%------------------------------------------------------------------------------
 %% APIs
@@ -62,7 +66,7 @@ get_env(Zone, Key) ->
 get_env(undefined, Key, Def) ->
     emqx_config:get_env(Key, Def);
 get_env(Zone, Key, Def) ->
-    try persistent_term:get({Zone, Key})
+    try persistent_term:get(?KEY(Zone, Key))
     catch error:badarg ->
         emqx_config:get_env(Key, Def)
     end.
@@ -84,7 +88,8 @@ stop() ->
 %%------------------------------------------------------------------------------
 
 init([]) ->
-    {ok, element(2, handle_info(reload, #{timer => undefined}))}.
+    _ = do_reload(),
+    {ok, #state{}}.
 
 handle_call(force_reload, _From, State) ->
     _ = do_reload(),
@@ -95,17 +100,13 @@ handle_call(Req, _From, State) ->
     {reply, ignored, State}.
 
 handle_cast({set_env, Zone, Key, Val}, State) ->
-    persistent_term:put({Zone, Key}, Val),
+    ok = persistent_term:put(?KEY(Zone, Key), Val),
     {noreply, State};
 
 handle_cast(Msg, State) ->
     ?LOG(error, "[Zone] Unexpected cast: ~p", [Msg]),
     {noreply, State}.
 
-handle_info(reload, State) ->
-    _ = do_reload(),
-    {noreply, ensure_reload_timer(State#{timer := undefined}), hibernate};
-
 handle_info(Info, State) ->
     ?LOG(error, "[Zone] Unexpected info: ~p", [Info]),
     {noreply, State}.
@@ -121,11 +122,6 @@ code_change(_OldVsn, State, _Extra) ->
 %%------------------------------------------------------------------------------
 
 do_reload() ->
-    [[persistent_term:put({Zone, Key}, Val)
-      || {Key, Val} <- Opts]
-     || {Zone, Opts} <- emqx_config:get_env(zones, [])].
+    [ persistent_term:put(?KEY(Zone, Key), Val)
+      || {Zone, Opts} <- emqx_config:get_env(zones, []), {Key, Val} <- Opts ].
 
-ensure_reload_timer(State = #{timer := undefined}) ->
-    State#{timer := erlang:send_after(timer:minutes(5), self(), reload)};
-ensure_reload_timer(State) ->
-    State.