Set layer state to stopped on pause. (#818)

* Set layer state to `stopped` on pause.

Previously, on pause, the worker was let run and declare
layer gone 1/2 a second (or whatever the stream tracker window
is set for) later.

But, when rapidly changing mute/unmute, the following cuold happen
and layer changes may be missed
- Available layers - 0, 1, 2
- Mute
- Before layer gone detected, unumute. Because of this layer gone
  is not reported and available layers stay at 0, 1, 2.
- Stream tracker is reset on unmute to enable quick detection of layer
  start.
- If all layers start back up, no issues.
- But, if the layers do not start back up, there is no layer start
  firing and the available layers are still 0, 1, 2 which is incorrect.

* exempt handling when paused

pkg/sfu/streamtracker.go

@@ -165,13 +165,22 @@ func (s *StreamTracker) resetLocked() {
 
 func (s *StreamTracker) SetPaused(paused bool) {
 	s.lock.Lock()
-	defer s.lock.Unlock()
 
 	s.paused = paused
 
+	status := s.status
+	changed := false
 	if !paused {
 		s.resetLocked()
+	} else {
+		// bump generation to trigger exit of current worker
+		s.generation.Inc()
+
+		status, changed = s.maybeSetStatus(StreamStatusStopped)
 	}
+	s.lock.Unlock()
+
+	s.maybeNotifyStatus(status, changed)
 }
 
 // Observe a packet that's received

pkg/sfu/streamtrackermanager.go

@@ -72,6 +72,7 @@ type StreamTrackerManager struct {
 
 	availableLayers  []int32
 	maxExpectedLayer int32
+	paused           bool
 
 	onAvailableLayersChanged     func(availableLayers []int32)
 	onBitrateAvailabilityChanged func()
@@ -137,11 +138,15 @@ func (s *StreamTrackerManager) AddTracker(layer int32) *StreamTracker {
 				}
 			}
 
-			s.lock.RLock()
-			maxExpectedLayer := s.maxExpectedLayer
-			s.lock.RUnlock()
+			if exempt {
+				s.lock.RLock()
+				if layer > s.maxExpectedLayer || s.paused {
+					exempt = false
+				}
+				s.lock.RUnlock()
+			}
 
-			if !exempt || layer > maxExpectedLayer {
+			if !exempt {
 				s.removeAvailableLayer(layer)
 			} else {
 				s.logger.Debugw("not removing exempt layer", "layer", layer)
@@ -183,6 +188,7 @@ func (s *StreamTrackerManager) RemoveAllTrackers() {
 	}
 	s.availableLayers = make([]int32, 0)
 	s.maxExpectedLayer = DefaultMaxLayerSpatial
+	s.paused = false
 	s.lock.Unlock()
 
 	for _, tracker := range trackers {
@@ -200,9 +206,10 @@ func (s *StreamTrackerManager) GetTracker(layer int32) *StreamTracker {
 }
 
 func (s *StreamTrackerManager) SetPaused(paused bool) {
-	s.lock.RLock()
+	s.lock.Lock()
+	s.paused = paused
 	trackers := s.trackers
-	s.lock.RUnlock()
+	s.lock.Unlock()
 
 	for _, tracker := range trackers {
 		if tracker != nil {