From cd52961b4b625d2aa1c135303845d91bcb8fc66b Mon Sep 17 00:00:00 2001
From: Tristan Sloughter <t@crashfast.com>
Date: Thu, 21 May 2020 09:19:21 -0600
Subject: [PATCH] efficient event execution on prefix lookup

---
 src/telemetry_handler_table.erl |  8 ++++----
 test/telemetry_SUITE.erl        | 24 ++++++++++++++----------
 2 files changed, 18 insertions(+), 14 deletions(-)

diff --git a/src/telemetry_handler_table.erl b/src/telemetry_handler_table.erl
index 8fd1eab..d8b16c6 100644
--- a/src/telemetry_handler_table.erl
+++ b/src/telemetry_handler_table.erl
@@ -45,7 +45,7 @@ delete(HandlerId) ->
 -spec list_for_event(telemetry:event_name()) -> [#handler{}].
 list_for_event(EventName) ->
     try
-        ets:lookup(?MODULE, EventName)
+        ets:match_object(?MODULE, match_pattern_for_prefix(EventName))
     catch
         error:badarg ->
             ?LOG_WARNING("Failed to lookup telemetry handlers. "
@@ -67,7 +67,7 @@ handle_call({insert, HandlerId, EventNames, Function, Config}, _From, State) ->
                                      _='_'}) of
         [] ->
             Objects = [#handler{id=HandlerId,
-                                event_name=EventName,
+                                event_name=EventName ++ [HandlerId],
                                 function=Function,
                                 config=Config} || EventName <- EventNames],
             ets:insert(?MODULE, Objects),
@@ -77,7 +77,7 @@ handle_call({insert, HandlerId, EventNames, Function, Config}, _From, State) ->
     end;
 handle_call({delete, HandlerId}, _From, State) ->
     case ets:select_delete(?MODULE, [{#handler{id=HandlerId,
-                                              _='_'}, [], [true]}]) of
+                                               _='_'}, [], [true]}]) of
         0 ->
             {reply, {error, not_found}, State};
         _ ->
@@ -99,7 +99,7 @@ terminate(_Reason, _State) ->
 %%
 
 create_table() ->
-    ets:new(?MODULE, [duplicate_bag, protected, named_table,
+    ets:new(?MODULE, [ordered_set, protected, named_table,
                       {keypos, 3}, {read_concurrency, true}]).
 
 match_pattern_for_prefix(EventPrefix) ->
diff --git a/test/telemetry_SUITE.erl b/test/telemetry_SUITE.erl
index 6c1b878..d093fae 100644
--- a/test/telemetry_SUITE.erl
+++ b/test/telemetry_SUITE.erl
@@ -69,8 +69,9 @@ list_handlers(Config) ->
     HandlerFun = fun ?MODULE:echo_event/4,
     telemetry:attach(HandlerId, Event, HandlerFun, HandlerConfig),
 
+    EventName = Event  ++ [HandlerId],
     ?assertMatch([#{id := HandlerId,
-                    event_name := Event,
+                    event_name := EventName,
                     function := HandlerFun,
                     config := HandlerConfig}],
                  telemetry:list_handlers(Event)).
@@ -86,8 +87,9 @@ list_for_prefix(Config) ->
     HandlerFun = fun ?MODULE:echo_event/4,
     telemetry:attach(HandlerId, Event, HandlerFun, HandlerConfig),
 
+    EventName = Event ++ [HandlerId],
     [?assertMatch([#{id := HandlerId,
-                     event_name := Event,
+                     event_name := EventName,
                      function := HandlerFun,
                      config := HandlerConfig}],
                   telemetry:list_handlers(Prefix)) || Prefix <- [Prefix1, Prefix2, Prefix3]],
@@ -101,8 +103,9 @@ detach_on_exception(Config) ->
     HandlerFun = fun ?MODULE:raise_on_event/4,
     telemetry:attach(HandlerId, Event, HandlerFun, []),
 
+    EventName = Event ++ [HandlerId],
     ?assertMatch([#{id := HandlerId,
-                    event_name := Event,
+                    event_name := EventName,
                     function := HandlerFun,
                     config := []}],
                  telemetry:list_handlers(Event)),
@@ -148,11 +151,11 @@ no_execute_on_prefix(Config) ->
     telemetry:execute(Prefix, Measurements, Metadata),
 
     receive
-        {event, Event, Measurements, Metadata, HandlerConfig} ->
-            ct:fail(prefix_executed)
-    after
-        300 ->
+        {event, Prefix, Measurements, Metadata, HandlerConfig} ->
             ok
+    after
+        1000 ->
+            ct:fail(timeout)
     end.
 
 %% handler is not invoked when event more specific than the one it's attached to is emitted
@@ -233,10 +236,11 @@ list_handler_on_many(Config) ->
     telemetry:attach_many(HandlerId, [Event1, Event2, Event3], HandlerFun, HandlerConfig),
 
     lists:foreach(fun(Event) ->
+                          EventName = Event ++ [HandlerId],
                           ?assertMatch([#{id := HandlerId,
-                                          event_name := Event,
+                                          event_name := EventName,
                                           function := HandlerFun,
-                                          config := EventConfig}],
+                                          config := _EventConfig}],
                                        telemetry:list_handlers(Event))
     end, [Event1, Event2, Event3]).
 
@@ -295,7 +299,7 @@ default_metadata(Config) ->
     end.
 
 % Ensure calling execute is safe when the telemetry application is off
-off_execute(Config) ->
+off_execute(_Config) ->
     application:stop(telemetry),
     telemetry:execute([event, name], #{}, #{}),
     application:ensure_all_started(telemetry).