feat: Use ets for last-known server-time. (#136)

Addresses main bottleneck of #132.

Author: kinyoklion

src/ldclient_event_process_server.erl

@@ -27,10 +27,11 @@
     global_private_attributes := ldclient_config:private_attributes(),
     events_uri := string(),
     tag := atom(),
-    dispatcher_state := any(),
-    last_server_time := integer()
+    dispatcher_state := any()
 }.
 
+-define(TABLE_PREFIX, "event_process_state").
+
 %%===================================================================
 %% API
 %%===================================================================
@@ -46,8 +47,17 @@ send_events(Tag, Events, SummaryEvent) ->
 
 -spec get_last_server_time(Tag :: atom()) -> integer().
 get_last_server_time(Tag) ->
-    ServerName = get_local_reg_name(Tag),
-    gen_server:call(ServerName, {get_last_server_time}).
+    TableName = ets_table_name(Tag),
+    case ets:info(TableName) of
+        undefined ->
+            0;
+        _ ->
+            case ets:lookup(TableName, last_known_server_time) of
+                [] -> 0;
+                [{last_known_server_time, LastKnownServerTime}] -> LastKnownServerTime
+            end
+    end.
+
 
 %%===================================================================
 %% Supervision
@@ -67,6 +77,7 @@ start_link(Tag) ->
     {ok, State :: state()} | {ok, State :: state(), timeout() | hibernate} |
     {stop, Reason :: term()} | ignore.
 init([Tag]) ->
+    _Tid = ets:new(ets_table_name(Tag), [set, named_table, {read_concurrency, true}]),
     SdkKey = ldclient_config:get_value(Tag, sdk_key),
     Dispatcher = ldclient_config:get_value(Tag, events_dispatcher),
     GlobalPrivateAttributes = ldclient_config:get_value(Tag, private_attributes),
@@ -77,8 +88,7 @@ init([Tag]) ->
         global_private_attributes => GlobalPrivateAttributes,
         events_uri => EventsUri,
         tag => Tag,
-        dispatcher_state =>  Dispatcher:init(Tag, SdkKey),
-        last_server_time => 0
+        dispatcher_state =>  Dispatcher:init(Tag, SdkKey)
     },
     {ok, State}.
 
@@ -90,8 +100,6 @@ init([Tag]) ->
 -spec handle_call(Request :: term(), From :: from(), State :: state()) ->
     {reply, Reply :: term(), NewState :: state()} |
     {stop, normal, {error, atom(), term()}, state()}.
-handle_call({get_last_server_time}, _From, #{last_server_time := LastServerTime} = State) ->
-    {reply, LastServerTime, State};
 handle_call(_Request, _From, State) ->
     {reply, ok, State}.
 
@@ -101,7 +109,8 @@ handle_cast({send_events, Events, SummaryEvent},
         dispatcher := Dispatcher,
         global_private_attributes := GlobalPrivateAttributes,
         events_uri := Uri,
-        dispatcher_state := DispatcherState
+        dispatcher_state := DispatcherState,
+        tag := Tag
     } = State) ->
     FormattedSummaryEvent = format_summary_event(SummaryEvent),
     FormattedEvents = format_events(Events, GlobalPrivateAttributes),
@@ -111,7 +120,8 @@ handle_cast({send_events, Events, SummaryEvent},
        ok ->
            State;
        {ok, Date} ->
-           State#{last_server_time => Date};
+           ets:insert(ets_table_name(Tag), {last_known_server_time, Date}),
+           State;
        {error, temporary, _Reason} ->
            erlang:send_after(1000, self(), {send, OutputEvents, PayloadId}),
            State;
@@ -321,3 +331,6 @@ send(Dispatcher, DispatcherState, OutputEvents, PayloadId, Uri) ->
 -spec get_local_reg_name(Tag :: atom()) -> atom().
 get_local_reg_name(Tag) ->
     list_to_atom("ldclient_event_process_server_" ++ atom_to_list(Tag)).
+
+-spec ets_table_name(Tag :: atom()) -> atom().
+ets_table_name(Tag) -> list_to_atom(?TABLE_PREFIX ++ atom_to_list(Tag)).