EventPublisher: docstrings and getTopicBuffer

also rename commitCh -> publishCh

agent/consul/state/event_publisher.go

@@ -28,7 +28,7 @@ type EventPublisher struct {
 	// not that expensive, but having a cache for a few seconds can help
 	// de-duplicate building the same snapshot over and over again when a
 	// thundering herd of watchers all subscribe to the same topic within a few
-	// seconds. TODO
+	// seconds.
 	snapCacheTTL time.Duration
 
 	// This lock protects the topicBuffers, snapCache and subsByToken maps.
@@ -38,8 +38,8 @@ type EventPublisher struct {
 	// for a topic.
 	topicBuffers map[stream.Topic]*stream.EventBuffer
 
-	// snapCache stores the head of any snapshot buffers still in cache if caching
-	// is enabled.
+	// snapCache if a cache of EventSnapshots indexed by topic and key.
+	// TODO: new struct for snapCache and snapFns and snapCacheTTL
 	snapCache map[stream.Topic]map[string]*stream.EventSnapshot
 
 	// snapFns is the set of snapshot functions that were registered bound to the
@@ -51,9 +51,10 @@ type EventPublisher struct {
 	// ACL permissions change.
 	subsByToken map[string]map[*stream.SubscribeRequest]*stream.Subscription
 
-	// commitCh decouples the Commit call in the FSM hot path from distributing
-	// the resulting events.
-	commitCh chan commitUpdate
+	// publishCh is used to send messages from an active txn to a goroutine which
+	// publishes events, so that publishing can happen asynchronously from
+	// the Commit call in the FSM hot path.
+	publishCh chan commitUpdate
 }
 
 type commitUpdate struct {
@@ -70,7 +71,7 @@ func NewEventPublisher(store *Store, topicBufferSize int, snapCacheTTL time.Dura
 		snapCache:       make(map[stream.Topic]map[string]*stream.EventSnapshot),
 		snapFns:         make(map[stream.Topic]stream.SnapFn),
 		subsByToken:     make(map[string]map[*stream.SubscribeRequest]*stream.Subscription),
-		commitCh:        make(chan commitUpdate, 64),
+		publishCh:       make(chan commitUpdate, 64),
 	}
 
 	// create a local handler table
@@ -98,7 +99,7 @@ func (e *EventPublisher) publishChanges(tx *txn, changes memdb.Changes) error {
 			events = append(events, es...)
 		}
 	}
-	e.commitCh <- commitUpdate{
+	e.publishCh <- commitUpdate{
 		// TODO: document why it must be created here, and not in the new thread
 		//
 		// Create a new transaction since it's going to be used from a different
@@ -113,7 +114,7 @@ func (e *EventPublisher) publishChanges(tx *txn, changes memdb.Changes) error {
 
 func (e *EventPublisher) handleUpdates() {
 	for {
-		update := <-e.commitCh
+		update := <-e.publishCh
 		e.sendEvents(update)
 	}
 }
@@ -158,15 +159,22 @@ func (e *EventPublisher) sendEvents(update commitUpdate) {
 		eventsByTopic[event.Topic] = append(eventsByTopic[event.Topic], event)
 	}
 
-	// Deliver events
 	for topic, events := range eventsByTopic {
-		buf, ok := e.topicBuffers[topic]
-		if !ok {
-			buf = stream.NewEventBuffer()
-			e.topicBuffers[topic] = buf
-		}
-		buf.Append(events)
+		e.getTopicBuffer(topic).Append(events)
+	}
+}
+
+// getTopicBuffer for the topic. Creates a new event buffer if one does not
+// already exist.
+//
+// EventPublisher.lock must be held to call this method.
+func (e *EventPublisher) getTopicBuffer(topic stream.Topic) *stream.EventBuffer {
+	buf, ok := e.topicBuffers[topic]
+	if !ok {
+		buf = stream.NewEventBuffer()
+		e.topicBuffers[topic] = buf
 	}
+	return buf
 }
 
 // handleACLUpdate handles an ACL token/policy/role update. This method assumes
@@ -250,11 +258,7 @@ func (e *EventPublisher) Subscribe(
 
 	// Ensure there is a topic buffer for that topic so we start capturing any
 	// future published events.
-	buf, ok := e.topicBuffers[req.Topic]
-	if !ok {
-		buf = stream.NewEventBuffer()
-		e.topicBuffers[req.Topic] = buf
-	}
+	buf := e.getTopicBuffer(req.Topic)
 
 	// See if we need a snapshot
 	topicHead := buf.Head()