hls: improve muxer performance (#5660)

use a mutex instead of a channel to get current instance.

internal/servers/hls/muxer.go

@@ -44,10 +44,6 @@ type muxerGetInstanceRes struct {
 	cumulatedOutboundFramesDiscarded uint64
 }
 
-type muxerGetInstanceReq struct {
-	res chan muxerGetInstanceRes
-}
-
 type muxer struct {
 	parentCtx       context.Context
 	remoteAddr      string
@@ -71,8 +67,9 @@ type muxer struct {
 	lastRequestTime atomic.Int64
 	bytesSent       atomic.Uint64
 
-	// in
-	chGetInstance chan muxerGetInstanceReq
+	instanceMutex                    sync.RWMutex
+	instance                         *muxerInstance
+	cumulatedOutboundFramesDiscarded uint64
 }
 
 func (m *muxer) initialize() {
@@ -83,7 +80,6 @@ func (m *muxer) initialize() {
 	m.created = time.Now()
 	m.lastRequestTime.Store(time.Now().UnixNano())
 	m.bytesSent.Store(0)
-	m.chGetInstance = make(chan muxerGetInstanceReq)
 
 	m.Log(logger.Info, "created %s", func() string {
 		if m.remoteAddr == "" {
@@ -92,6 +88,9 @@ func (m *muxer) initialize() {
 		return "(requested by " + m.remoteAddr + ")"
 	}())
 
+	// block first request to getInstance() until the first instance is available
+	m.instanceMutex.Lock()
+
 	m.wg.Add(1)
 	go m.run()
 }
@@ -132,6 +131,7 @@ func (m *muxer) runInner() error {
 		},
 	})
 	if err != nil {
+		m.instanceMutex.Unlock()
 		return err
 	}
 
@@ -139,27 +139,30 @@ func (m *muxer) runInner() error {
 
 	defer m.path.RemoveReader(defs.PathRemoveReaderReq{Author: m})
 
-	mi, err := m.createInstance(res.Stream)
+	tmp, err := m.createInstance(res.Stream)
 	if err != nil {
 		if m.remoteAddr != "" || errors.Is(err, hls.ErrNoSupportedCodecs) {
+			m.instanceMutex.Unlock()
 			return err
 		}
 
 		m.Log(logger.Error, err.Error())
-		mi = nil
 	}
 
+	m.instance = tmp
+	m.instanceMutex.Unlock()
+
 	defer func() {
-		if mi != nil {
-			mi.close()
+		if m.instance != nil {
+			m.closeInstance()
 		}
 	}()
 
 	var instanceError chan error
 	var recreateTimer *time.Timer
 
-	if mi != nil {
-		instanceError = mi.errorChan()
+	if m.instance != nil {
+		instanceError = m.instance.errorChan()
 		recreateTimer = emptyTimer()
 	} else {
 		instanceError = make(chan error)
@@ -173,36 +176,29 @@ func (m *muxer) runInner() error {
 		activityCheckTimer = emptyTimer()
 	}
 
-	cumulatedOutboundFramesDiscarded := uint64(0)
-
 	for {
 		select {
-		case req := <-m.chGetInstance:
-			req.res <- muxerGetInstanceRes{
-				instance:                         mi,
-				cumulatedOutboundFramesDiscarded: cumulatedOutboundFramesDiscarded,
-			}
-
 		case err = <-instanceError:
 			if m.remoteAddr != "" {
 				return err
 			}
 
 			m.Log(logger.Error, err.Error())
-			mi.close()
-			cumulatedOutboundFramesDiscarded += mi.reader.OutboundFramesDiscarded()
-			mi = nil
+			m.closeInstance()
 			instanceError = make(chan error)
 			recreateTimer = time.NewTimer(recreatePause)
 
 		case <-recreateTimer.C:
-			mi, err = m.createInstance(res.Stream)
+			tmp, err = m.createInstance(res.Stream)
 			if err != nil {
 				m.Log(logger.Error, err.Error())
-				mi = nil
 				recreateTimer = time.NewTimer(recreatePause)
 			} else {
-				instanceError = mi.errorChan()
+				m.instanceMutex.Lock()
+				m.instance = tmp
+				m.instanceMutex.Unlock()
+
+				instanceError = m.instance.errorChan()
 			}
 
 		case <-activityCheckTimer.C:
@@ -218,6 +214,16 @@ func (m *muxer) runInner() error {
 	}
 }
 
+func (m *muxer) closeInstance() {
+	m.instanceMutex.Lock()
+	m.cumulatedOutboundFramesDiscarded += m.instance.reader.OutboundFramesDiscarded()
+	var tmp *muxerInstance
+	tmp, m.instance = m.instance, nil
+	m.instanceMutex.Unlock()
+
+	tmp.close()
+}
+
 func (m *muxer) createInstance(strm *stream.Stream) (*muxerInstance, error) {
 	mi := &muxerInstance{
 		variant:         m.variant,
@@ -235,14 +241,12 @@ func (m *muxer) createInstance(strm *stream.Stream) (*muxerInstance, error) {
 }
 
 func (m *muxer) getInstance() muxerGetInstanceRes {
-	req := muxerGetInstanceReq{res: make(chan muxerGetInstanceRes)}
+	m.instanceMutex.RLock()
+	defer m.instanceMutex.RUnlock()
 
-	select {
-	case m.chGetInstance <- req:
-		return <-req.res
-
-	case <-m.ctx.Done():
-		return muxerGetInstanceRes{}
+	return muxerGetInstanceRes{
+		instance:                         m.instance,
+		cumulatedOutboundFramesDiscarded: m.cumulatedOutboundFramesDiscarded,
 	}
 }