dont send duplicate updates

pubsub/pt.go

@@ -15,10 +15,15 @@ const (
 	Done
 )
 
+type subChan struct {
+	c               chan<- string
+	lastUpdateIndex int
+}
+
 type subscriberState struct {
-	step     Step
-	m        sync.Mutex
-	subChans []chan<- string
+	step Step
+	m    sync.Mutex
+	sc   []subChan
 }
 
 type InvalidState struct{ Step Step }
@@ -82,23 +87,25 @@ func (pt *progressTracker) Publish(id string) (chan<- string, error) {
 		prodChanOpen := true
 		ticker := time.NewTicker(100 * time.Millisecond)
 		defer ticker.Stop()
+		lastUpdateIndex := 0
 		for range ticker.C {
-			done := false
-			for !done && prodChanOpen {
+		LoopReader:
+			for prodChanOpen {
 				select {
 				case update, prodChanOpen = <-prodChan:
+					lastUpdateIndex++
 				default:
-					done = true
+					break LoopReader
 				}
 			}
-			var scs []chan<- string
+			var scs []subChan
 			func() {
 				state.m.Lock()
 				defer state.m.Unlock()
-				scs = state.subChans
+				scs = state.sc
 				if !prodChanOpen {
 					for _, subChan := range scs {
-						close(subChan)
+						close(subChan.c)
 					}
 					state.step = Done
 				}
@@ -107,9 +114,12 @@ func (pt *progressTracker) Publish(id string) (chan<- string, error) {
 				return
 			}
 			for _, subChan := range scs {
-				select {
-				case subChan <- update:
-				default:
+				if subChan.lastUpdateIndex != lastUpdateIndex {
+					select {
+					case subChan.c <- update:
+						subChan.lastUpdateIndex = lastUpdateIndex
+					default:
+					}
 				}
 			}
 		}
@@ -119,6 +129,7 @@ func (pt *progressTracker) Publish(id string) (chan<- string, error) {
 
 func (pt *progressTracker) Subscribe(id string) <-chan string {
 	c := make(chan string, 1)
+	sc := subChan{c: c}
 	var state *subscriberState
 	func() {
 		pt.m.Lock()
@@ -126,8 +137,8 @@ func (pt *progressTracker) Subscribe(id string) <-chan string {
 		state = pt.subscribers[id]
 		if state == nil {
 			pt.subscribers[id] = &subscriberState{
-				step:     NotStarted,
-				subChans: []chan<- string{c},
+				step: NotStarted,
+				sc:   []subChan{sc},
 			}
 		}
 	}()
@@ -139,6 +150,6 @@ func (pt *progressTracker) Subscribe(id string) <-chan string {
 	if state.step == Done {
 		return nil
 	}
-	state.subChans = append(state.subChans, c)
+	state.sc = append(state.sc, sc)
 	return c
 }