fix deadlocks in track subscription

pkg/rtc/mediatrack.go

@@ -212,8 +212,11 @@ func (t *MediaTrack) AddSubscriber(sub types.Participant) error {
 	t.subscribedTracks[sub.ID()] = subTrack
 
 	t.receiver.AddDownTrack(downTrack, true)
-	sub.AddSubscribedTrack(t.params.ParticipantID, subTrack)
-	sub.Negotiate()
+	// since sub will lock, run it in a gorountine to avoid deadlocks
+	go func() {
+		sub.AddSubscribedTrack(t.params.ParticipantID, subTrack)
+		sub.Negotiate()
+	}()
 
 	t.params.Stats.AddSubscribedTrack(t.kind.String())
 	return nil

pkg/rtc/room.go

@@ -318,14 +318,12 @@ func (r *Room) OnParticipantChanged(f func(participant types.Participant)) {
 	r.onParticipantChanged = f
 }
 
+// checks if participant should be autosubscribed to new tracks, assumes lock is already acquired
 func (r *Room) autoSubscribe(participant types.Participant) bool {
 	if !participant.CanSubscribe() {
 		return false
 	}
 
-	r.lock.RLock()
-	defer r.lock.RUnlock()
-
 	opts := r.participantOpts[participant.Identity()]
 	// default to true if no options are set
 	if opts != nil && !opts.AutoSubscribe {
@@ -402,7 +400,10 @@ func (r *Room) onDataPacket(source types.Participant, dp *livekit.DataPacket) {
 }
 
 func (r *Room) subscribeToExistingTracks(p types.Participant) {
-	if !r.autoSubscribe(p) {
+	r.lock.RLock()
+	shouldSubscribe := r.autoSubscribe(p)
+	r.lock.RUnlock()
+	if !shouldSubscribe {
 		return
 	}