From 4480ccb6cb8fd911d5fd20f436a0a84132c9ca7d Mon Sep 17 00:00:00 2001
From: Raimo Niskanen <raimo@erlang.org>
Date: Tue, 7 Feb 2017 18:03:13 +0100
Subject: Remove event timer optimization

Handle the event timer more like other timers and do not optimize
the odd case of combining an event timeout with inserting
custom events, wich by definition cancels the event timeout.
---
 lib/stdlib/src/gen_statem.erl | 86 ++++++++++++++++---------------------------
 1 file changed, 31 insertions(+), 55 deletions(-)

(limited to 'lib')

diff --git a/lib/stdlib/src/gen_statem.erl b/lib/stdlib/src/gen_statem.erl
index 6d9a828319..7a23a2a681 100644
--- a/lib/stdlib/src/gen_statem.erl
+++ b/lib/stdlib/src/gen_statem.erl
@@ -1131,16 +1131,14 @@ loop_event_result(
     %% Place next events last in reversed queue
     Events_2R = lists:reverse(Events_1, NextEventsR),
     %% Enqueue immediate timeout events and start event timer
-    {TimerRefs_3,TimerTypes_3,Events_3R} =
-	process_timeout_events(
-	  TimerRefs_2, TimerTypes_2, TimeoutEvents, Events_2R),
+    Events_3R =	prepend_timeout_events(TimeoutEvents, Events_2R),
     S_1 =
 	S_0#{
 	  state := NextState,
 	  data := NewData,
 	  postponed := P_2,
-	  timer_refs := TimerRefs_3,
-	  timer_types := TimerTypes_3,
+	  timer_refs := TimerRefs_2,
+	  timer_types := TimerTypes_2,
 	  cancel_timers := CancelTimers_2,
 	  hibernate := Hibernate},
     case lists:reverse(Events_3R) of
@@ -1361,7 +1359,7 @@ parse_enter_actions(Debug, S, State, Actions, Hibernate, TimeoutsR) ->
     
 parse_actions(Debug, S, State, Actions) ->
     Hibernate = false,
-    TimeoutsR = [],
+    TimeoutsR = [{timeout,infinity,infinity}], %% Will cancel event timer
     Postpone = false,
     NextEventsR = [],
     parse_actions(
@@ -1413,12 +1411,9 @@ parse_actions(
 	    {error,
 	     {bad_action_from_state_function,Action},
 	     ?STACKTRACE()};
-	{timeout,infinity,_} ->
-	    %% Ignore - timeout will never happen and is already cancelled
-	    parse_actions(
-	      Debug, S, State, Actions,
-	      Hibernate, TimeoutsR, Postpone, NextEventsR);
-	{timeout,Time,_} = Timeout when is_integer(Time), Time >= 0 ->
+	{timeout,Time,_} = Timeout
+	  when is_integer(Time), Time >= 0;
+	       Time =:= infinity ->
 	    parse_actions(
 	      Debug, S, State, Actions,
 	      Hibernate, [Timeout|TimeoutsR], Postpone, NextEventsR);
@@ -1426,11 +1421,9 @@ parse_actions(
 	    {error,
 	     {bad_action_from_state_function,Action},
 	     ?STACKTRACE()};
-	infinity -> % Ignore - timeout will never happen
-	    parse_actions(
-	      Debug, S, State, Actions,
-	      Hibernate, TimeoutsR, Postpone, NextEventsR);
-	Time when is_integer(Time), Time >= 0 ->
+	Time
+	  when is_integer(Time), Time >= 0;
+	       Time =:= infinity ->
 	    Timeout = {timeout,Time,Time},
 	    parse_actions(
 	      Debug, S, State, Actions,
@@ -1493,11 +1486,6 @@ parse_timers(
 	    %% Unseen type - handle
 	    NewSeen = Seen#{TimerType => true},
 	    if
-		TimerType =:= timeout ->
-		    %% Handle event timer later
-		    parse_timers(
-		      TimerRefs, TimerTypes, CancelTimers, TimeoutsR,
-		      NewSeen, [Timeout|TimeoutEvents]);
 		Time =:= infinity ->
 		    %% Cancel any running timer
 		    {NewTimerTypes,NewCancelTimers} =
@@ -1541,39 +1529,27 @@ parse_timers(
 	    end
     end.
 
-%% Enqueue immediate timeout events and start event timer
-process_timeout_events(TimerRefs, TimerTypes, [], EventsR) ->
-    {TimerRefs, TimerTypes, EventsR};
-process_timeout_events(
-  TimerRefs, TimerTypes,
-  [{timeout,0,TimerMsg}|TimeoutEvents], []) ->
-    %% No enqueued events - insert a timeout zero event
-    TimeoutEvent = {timeout,TimerMsg},
-    process_timeout_events(
-      TimerRefs, TimerTypes,
-      TimeoutEvents, [TimeoutEvent]);
-process_timeout_events(
-  TimerRefs, TimerTypes,
-  [{timeout,Time,TimerMsg}], []) ->
-    %% No enqueued events - start event timer
-    TimerRef = erlang:start_timer(Time, self(), TimerMsg),
-    process_timeout_events(
-      TimerRefs#{TimerRef => timeout}, TimerTypes#{timeout => TimerRef},
-      [], []);
-process_timeout_events(
-  TimerRefs, TimerTypes,
-  [{timeout,_Time,_TimerMsg}|TimeoutEvents], EventsR) ->
-    %% There will be some other event so optimize by not starting
-    %% an event timer to just have to cancel it again
-    process_timeout_events(
-      TimerRefs, TimerTypes,
-      TimeoutEvents, EventsR);
-process_timeout_events(
-  TimerRefs, TimerTypes,
-  [{_TimeoutType,_TimeoutMsg} = TimeoutEvent|TimeoutEvents], EventsR) ->
-    process_timeout_events(
-      TimerRefs, TimerTypes,
-      TimeoutEvents, [TimeoutEvent|EventsR]).
+%% Enqueue immediate timeout events (timeout 0 events)
+%%
+%% Event timer timeout 0 events gets special treatment since
+%% an event timer is cancelled by any received event,
+%% so if there are enqueued events before the event timer
+%% timeout 0 event - the event timer is cancelled hence no event.
+%%
+%% Other (state_timeout) timeout 0 events that are after
+%% the event timer timeout 0 events are considered to
+%% belong to timers that were started after the event timer
+%% timeout 0 event fired, so they do not cancel the event timer.
+%%
+prepend_timeout_events([], EventsR) ->
+    EventsR;
+prepend_timeout_events([{timeout,_} = TimeoutEvent|TimeoutEvents], []) ->
+    prepend_timeout_events(TimeoutEvents, [TimeoutEvent]);
+prepend_timeout_events([{timeout,_}|TimeoutEvents], EventsR) ->
+    prepend_timeout_events(TimeoutEvents, EventsR);
+prepend_timeout_events([TimeoutEvent|TimeoutEvents], EventsR) ->
+    %% Just prepend all others
+    prepend_timeout_events(TimeoutEvents, [TimeoutEvent|EventsR]).
 
 
 
-- 
cgit v1.2.3