Introducing OpsQueue (#463)

* Introducing OpsQueue

Creating a PR to get feedback on standardizing on this concept.

Can be used for callbacks.
Already a couple of places use this construct. Wondering if we
should standardize on this across the board.
Just changing one place to use the new struct. Another place
that I know of which uses this pattern is the telemetry package.

* atomic flag -> bool

pkg/sfu/buffer/buffer.go

@@ -10,6 +10,7 @@ import (
 	"time"
 
 	"github.com/gammazero/deque"
+	"github.com/livekit/livekit-server/pkg/utils"
 	"github.com/livekit/protocol/logger"
 	"github.com/pion/rtcp"
 	"github.com/pion/rtp"
@@ -89,7 +90,8 @@ type Buffer struct {
 	onAudioLevel func(level uint8, durationMs uint32)
 	feedbackCB   func([]rtcp.Packet)
 	feedbackTWCC func(sn uint16, timeNS int64, marker bool)
-	callbackOps  chan func()
+
+	callbacksQueue *utils.OpsQueue
 
 	// logger
 	logger logger.Logger
@@ -109,12 +111,12 @@ type Options struct {
 // NewBuffer constructs a new Buffer
 func NewBuffer(ssrc uint32, vp, ap *sync.Pool) *Buffer {
 	b := &Buffer{
-		mediaSSRC:   ssrc,
-		videoPool:   vp,
-		audioPool:   ap,
-		pliThrottle: int64(500 * time.Millisecond),
-		logger:      logger.Logger(logger.GetLogger()), // will be reset with correct context via SetLogger
-		callbackOps: make(chan func(), 50),
+		mediaSSRC:      ssrc,
+		videoPool:      vp,
+		audioPool:      ap,
+		pliThrottle:    int64(500 * time.Millisecond),
+		logger:         logger.Logger(logger.GetLogger()), // will be reset with correct context via SetLogger
+		callbacksQueue: utils.NewOpsQueue(),
 	}
 	b.bitrate.Store(make([]int64, len(b.bitrateHelper)))
 	b.extPackets.SetMinCapacity(7)
@@ -132,7 +134,7 @@ func (b *Buffer) Bind(params webrtc.RTPParameters, codec webrtc.RTPCodecCapabili
 		return
 	}
 
-	go b.doCallbacks()
+	b.callbacksQueue.Start()
 
 	b.clockRate = codec.ClockRate
 	b.maxBitrate = int64(o.MaxBitRate)
@@ -190,12 +192,6 @@ func (b *Buffer) Bind(params webrtc.RTPParameters, codec webrtc.RTPCodecCapabili
 	b.logger.Debugw("NewBuffer", "MaxBitRate", o.MaxBitRate)
 }
 
-func (b *Buffer) doCallbacks() {
-	for op := range b.callbackOps {
-		op()
-	}
-}
-
 // Write adds an RTP Packet, out of order, new packet may be arrived later
 func (b *Buffer) Write(pkt []byte) (n int, err error) {
 	b.Lock()
@@ -273,7 +269,7 @@ func (b *Buffer) Close() error {
 		}
 		b.closed.set(true)
 		b.onClose()
-		close(b.callbackOps)
+		b.callbacksQueue.Stop()
 	})
 	return nil
 }
@@ -307,9 +303,9 @@ func (b *Buffer) SendPLI() {
 		&rtcp.PictureLossIndication{SenderSSRC: rand.Uint32(), MediaSSRC: b.mediaSSRC},
 	}
 
-	b.callbackOps <- func() {
+	b.callbacksQueue.Enqueue(func() {
 		b.feedbackCB(pli)
-	}
+	})
 }
 
 func (b *Buffer) SetRTT(rtt uint32) {
@@ -457,9 +453,9 @@ func (b *Buffer) processHeaderExtensions(p *rtp.Packet, arrivalTime int64) {
 		if ext := p.GetExtension(b.twccExt); len(ext) > 1 {
 			sn := binary.BigEndian.Uint16(ext[0:2])
 			marker := p.Marker
-			b.callbackOps <- func() {
+			b.callbacksQueue.Enqueue(func() {
 				b.feedbackTWCC(sn, arrivalTime, marker)
-			}
+			})
 		}
 	}
 
@@ -474,9 +470,9 @@ func (b *Buffer) processHeaderExtensions(p *rtp.Packet, arrivalTime int64) {
 				if (p.Timestamp - b.latestTSForAudioLevel) < (1 << 31) {
 					duration := (int64(p.Timestamp) - int64(b.latestTSForAudioLevel)) * 1e3 / int64(b.clockRate)
 					if duration > 0 {
-						b.callbackOps <- func() {
+						b.callbacksQueue.Enqueue(func() {
 							b.onAudioLevel(ext.Level, uint32(duration))
-						}
+						})
 					}
 
 					b.latestTSForAudioLevel = p.Timestamp
@@ -523,9 +519,9 @@ func (b *Buffer) doNACKs() {
 	}
 
 	if r, numSeqNumsNacked := b.buildNACKPacket(); r != nil {
-		b.callbackOps <- func() {
+		b.callbacksQueue.Enqueue(func() {
 			b.feedbackCB(r)
-		}
+		})
 		b.stats.TotalNACKs += uint32(numSeqNumsNacked)
 	}
 }
@@ -557,9 +553,9 @@ func (b *Buffer) doReports(arrivalTime int64) {
 
 	// RTCP reports
 	pkts := b.getRTCP()
-	b.callbackOps <- func() {
+	b.callbacksQueue.Enqueue(func() {
 		b.feedbackCB(pkts)
-	}
+	})
 }
 
 func (b *Buffer) buildNACKPacket() ([]rtcp.Packet, int) {