From d1d82656e75d9c65bad7127474d4b0774f929b3b Mon Sep 17 00:00:00 2001
From: Neil Alexander <neilalexander@users.noreply.github.com>
Date: Mon, 25 Jan 2021 16:23:49 +0000
Subject: [PATCH] Persist events/state in order

---
 roomserver/internal/input/input.go        | 45 +++--------------------
 roomserver/internal/input/input_events.go | 23 +++++++-----
 2 files changed, 20 insertions(+), 48 deletions(-)

diff --git a/roomserver/internal/input/input.go b/roomserver/internal/input/input.go
index 69cc0ca1..b16f1da5 100644
--- a/roomserver/internal/input/input.go
+++ b/roomserver/internal/input/input.go
@@ -39,13 +39,6 @@ type Inputer struct {
 	latestEventsMutexes sync.Map // room ID -> sync.Mutex
 }
 
-type inputTask struct {
-	ctx   context.Context
-	event *api.InputRoomEvent
-	wg    *sync.WaitGroup
-	err   error // written back by worker, only safe to read when all tasks are done
-}
-
 // WriteOutputEvents implements OutputRoomEventWriter
 func (r *Inputer) WriteOutputEvents(roomID string, updates []api.OutputEvent) error {
 	messages := make([]*sarama.ProducerMessage, len(updates))
@@ -94,40 +87,14 @@ func (r *Inputer) InputRoomEvents(
 	request *api.InputRoomEventsRequest,
 	response *api.InputRoomEventsResponse,
 ) {
-	// Create a wait group. Each task that we dispatch will call Done on
-	// this wait group so that we know when all of our events have been
-	// processed.
-	wg := &sync.WaitGroup{}
-	wg.Add(len(request.InputRoomEvents))
-	tasks := make([]*inputTask, len(request.InputRoomEvents))
-
 	for i := range request.InputRoomEvents {
-		tasks[i] = &inputTask{
-			ctx:   context.Background(),
-			event: &request.InputRoomEvents[i],
-			wg:    wg,
-		}
-		go func(task *inputTask) {
-			hooks.Run(hooks.KindNewEventReceived, task.event.Event)
-			_, task.err = r.processRoomEvent(task.ctx, task.event)
-			if task.err == nil {
-				hooks.Run(hooks.KindNewEventPersisted, task.event.Event)
-			}
-			task.wg.Done()
-		}(tasks[i])
-	}
-
-	// Wait for all of the workers to return results about our tasks.
-	wg.Wait()
-
-	// If any of the tasks returned an error, we should probably report
-	// that back to the caller.
-	for _, task := range tasks {
-		if task.err != nil {
-			response.ErrMsg = task.err.Error()
-			_, rejected := task.err.(*gomatrixserverlib.NotAllowed)
+		hooks.Run(hooks.KindNewEventReceived, &request.InputRoomEvents[i])
+		if _, err := r.processRoomEvent(context.Background(), &request.InputRoomEvents[i]); err == nil {
+			hooks.Run(hooks.KindNewEventPersisted, &request.InputRoomEvents[i])
+		} else {
+			response.ErrMsg = err.Error()
+			_, rejected := err.(*gomatrixserverlib.NotAllowed)
 			response.NotAllowed = rejected
-			return
 		}
 	}
 }
diff --git a/roomserver/internal/input/input_events.go b/roomserver/internal/input/input_events.go
index 2a558c48..ff60ec64 100644
--- a/roomserver/internal/input/input_events.go
+++ b/roomserver/internal/input/input_events.go
@@ -192,15 +192,20 @@ func (r *Inputer) processRoomEvent(
 
 	switch input.Kind {
 	case api.KindNew:
-		if err = r.updateLatestEvents(
-			ctx,                 // context
-			roomInfo,            // room info for the room being updated
-			stateAtEvent,        // state at event (below)
-			event,               // event
-			input.SendAsServer,  // send as server
-			input.TransactionID, // transaction ID
-			input.HasState,      // rewrites state?
-		); err != nil {
+		errch := make(chan error)
+		go func() {
+			errch <- r.updateLatestEvents(
+				ctx,                 // context
+				roomInfo,            // room info for the room being updated
+				stateAtEvent,        // state at event (below)
+				event,               // event
+				input.SendAsServer,  // send as server
+				input.TransactionID, // transaction ID
+				input.HasState,      // rewrites state?
+			)
+			close(errch)
+		}()
+		if err = <-errch; err != nil {
 			return "", fmt.Errorf("r.updateLatestEvents: %w", err)
 		}
 	case api.KindOld: