refactor: use mneisa:subscribe/1 for rule operations

apps/emqx_rule_engine/src/emqx_rule_registry.erl

@@ -21,6 +21,8 @@
 -include("rule_engine.hrl").
 -include_lib("emqx/include/logger.hrl").
 
+-logger_header("[RuleRegistry] ").
+
 -export([start_link/0]).
 
 %% Rule Management
@@ -242,7 +244,6 @@ remove_rules(Rules) ->
 
 %% @private
 insert_rule(Rule) ->
-    _ = ?CLUSTER_CALL(load_hooks_for_rule, [Rule]),
     mnesia:write(?RULE_TAB, Rule, write).
 
 %% @private
@@ -252,7 +253,6 @@ delete_rule(RuleId) when is_binary(RuleId) ->
         not_found -> ok
     end;
 delete_rule(Rule) ->
-    _ = ?CLUSTER_CALL(unload_hooks_for_rule, [Rule]),
     mnesia:delete_object(?RULE_TAB, Rule, write).
 
 load_hooks_for_rule(#rule{for = Topics}) ->
@@ -261,7 +261,9 @@ load_hooks_for_rule(#rule{for = Topics}) ->
 unload_hooks_for_rule(#rule{id = Id, for = Topics}) ->
     lists:foreach(fun(Topic) ->
             case get_rules_with_same_event(Topic) of
-                [#rule{id = Id}] -> %% we are now deleting the last rule
+                [] -> %% no rules left, we can safely unload the hook
+                    emqx_rule_events:unload(Topic);
+                [#rule{id = Id0}] when Id0 =:= Id-> %% we are now deleting the last rule
                     emqx_rule_events:unload(Topic);
                 _ -> ok
             end
@@ -463,20 +465,29 @@ delete_resource_type(Type) ->
 init([]) ->
     _TableId = ets:new(?KV_TAB, [named_table, set, public, {write_concurrency, true},
                                  {read_concurrency, true}]),
+    {ok, _} = mnesia:subscribe({table, ?RULE_TAB, detailed}),
     {ok, #{}}.
 
-handle_call({add_rules, Rules}, _From, State) ->
+handle_call({add_rules, []}, _From, State) ->
+    {reply, ok, State};
+handle_call({add_rules, Rules}, From, State) ->
     trans(fun lists:foreach/2, [fun insert_rule/1, Rules]),
-    _ = ?CLUSTER_CALL(update_rules_cache, []),
-    {reply, ok, State};
+    %% won't reply until the mnesia_table_event is received.
+    {noreply, State#{
+        callers_create => add_caller(maps:get(callers_create, State, #{}), Rules, From)
+    }};
 
-handle_call({remove_rules, Rules}, _From, State) ->
-    trans(fun lists:foreach/2, [fun delete_rule/1, Rules]),
-    _ = ?CLUSTER_CALL(update_rules_cache, []),
+handle_call({remove_rules, []}, _From, State) ->
     {reply, ok, State};
+handle_call({remove_rules, Rules}, From, State) ->
+    trans(fun lists:foreach/2, [fun delete_rule/1, Rules]),
+    %% won't reply until the mnesia_table_event is received.
+    {noreply, State#{
+        callers_delete => add_caller(maps:get(callers_delete, State, #{}), Rules, From)
+    }};
 
 handle_call(Req, _From, State) ->
-    ?LOG(error, "[RuleRegistry]: unexpected call - ~p", [Req]),
+    ?LOG(error, "unexpected call - ~p", [Req]),
     {reply, ignored, State}.
 
 handle_cast(update_rules_cache, State) ->
@@ -484,11 +495,31 @@ handle_cast(update_rules_cache, State) ->
     {noreply, State};
 
 handle_cast(Msg, State) ->
-    ?LOG(error, "[RuleRegistry]: unexpected cast ~p", [Msg]),
+    ?LOG(error, "unexpected cast ~p", [Msg]),
     {noreply, State}.
 
+handle_info({mnesia_table_event, {write, Tab, NewRule, _OldRules, _Tid} = Event}, State) ->
+    ?LOG(debug, "mnesia_table_event on tab: ~p, event: ~p~n", [Tab, Event]),
+    ok = load_hooks_for_rule(NewRule),
+    ok = update_rules_cache(),
+    {noreply, maybe_reply_callers(callers_create, NewRule#rule.id, State)};
+
+handle_info({mnesia_table_event, {Delete, _Tab, _What, [], _Tid}}, State)
+        when Delete =:= delete; Delete =:= delete_object ->
+    {noreply, State};
+
+handle_info({mnesia_table_event, {Delete, Tab, _What, OldRules, _Tid} = Event}, State)
+        when Delete =:= delete; Delete =:= delete_object ->
+    ?LOG(debug, "mnesia_table_event on tab: ~p, event: ~p~n", [Tab, Event]),
+    ok = lists:foreach(fun unload_hooks_for_rule/1, OldRules),
+    ok = update_rules_cache(),
+    NewState = lists:foldr(fun(R, AccState) ->
+            maybe_reply_callers(callers_delete, R#rule.id, AccState)
+        end, State, OldRules),
+    {noreply, NewState};
+
 handle_info(Info, State) ->
-    ?LOG(error, "[RuleRegistry]: unexpected info ~p", [Info]),
+    ?LOG(error, "unexpected info ~p", [Info]),
     {noreply, State}.
 
 terminate(_Reason, _State) ->
@@ -501,6 +532,22 @@ code_change(_OldVsn, State, _Extra) ->
 %% Private functions
 %%------------------------------------------------------------------------------
 
+add_caller(OldCallers, Rules, From) ->
+    RuleIds = lists:map(fun
+            (#rule{id = Id}) -> Id;
+            (Id) when is_binary(Id) -> Id
+        end, Rules),
+    maps:merge(OldCallers, maps:from_keys(RuleIds, From)).
+
+maybe_reply_callers(OperType, RuleId, State) ->
+    case maps:take(RuleId, maps:get(OperType, State, #{})) of
+        {Caller, NewState} ->
+            gen_server:reply(Caller, ok),
+            NewState;
+        error ->
+            State
+    end.
+
 get_all_records(Tab) ->
     %mnesia:dirty_match_object(Tab, mnesia:table_info(Tab, wild_pattern)).
     ets:tab2list(Tab).