store participant res sink in interface typed field (#1567)

pkg/rtc/participant.go

@@ -93,12 +93,12 @@ type ParticipantParams struct {
 type ParticipantImpl struct {
 	params ParticipantParams
 
-	isClosed     atomic.Bool
-	state        atomic.Value // livekit.ParticipantInfo_State
-	resSink      atomic.Value // routing.MessageSink
-	resSinkValid atomic.Bool
-	grants       *auth.ClaimGrants
-	isPublisher  atomic.Bool
+	isClosed    atomic.Bool
+	state       atomic.Value // livekit.ParticipantInfo_State
+	resSinkMu   sync.Mutex
+	resSink     routing.MessageSink
+	grants      *auth.ClaimGrants
+	isPublisher atomic.Bool
 
 	// when first connected
 	connectedAt time.Time

pkg/rtc/participant_signal.go

@@ -12,22 +12,15 @@ import (
 )
 
 func (p *ParticipantImpl) getResponseSink() routing.MessageSink {
-	if !p.resSinkValid.Load() {
-		return nil
-	}
-	sink := p.resSink.Load()
-	if s, ok := sink.(routing.MessageSink); ok {
-		return s
-	}
-	return nil
+	p.resSinkMu.Lock()
+	defer p.resSinkMu.Unlock()
+	return p.resSink
 }
 
 func (p *ParticipantImpl) SetResponseSink(sink routing.MessageSink) {
-	p.resSinkValid.Store(sink != nil)
-	if sink != nil {
-		// cannot store nil into atomic.Value
-		p.resSink.Store(sink)
-	}
+	p.resSinkMu.Lock()
+	defer p.resSinkMu.Unlock()
+	p.resSink = sink
 }
 
 func (p *ParticipantImpl) SendJoinResponse(joinResponse *livekit.JoinResponse) error {