snapshot of https://github.com/livekit/livekit.git @ 08c5433449c106943231037d0b892895f6e92d3b (2026-09-15)

pkg/sfu/utils/downtrackspreader.go

@@ -0,0 +1,129 @@
+// Copyright 2023 LiveKit, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package utils
+
+import (
+	"sync"
+
+	"github.com/livekit/protocol/livekit"
+	"github.com/livekit/protocol/logger"
+	"github.com/livekit/protocol/utils"
+)
+
+type sender interface {
+	SubscriberID() livekit.ParticipantID
+}
+
+type DownTrackSpreaderParams struct {
+	Threshold int
+	Logger    logger.Logger
+}
+
+type DownTrackSpreader[T sender] struct {
+	params DownTrackSpreaderParams
+
+	downTrackMu      sync.RWMutex
+	downTracks       map[livekit.ParticipantID]T
+	downTracksShadow []T
+}
+
+func NewDownTrackSpreader[T sender](params DownTrackSpreaderParams) *DownTrackSpreader[T] {
+	d := &DownTrackSpreader[T]{
+		params:     params,
+		downTracks: make(map[livekit.ParticipantID]T),
+	}
+
+	return d
+}
+
+func (d *DownTrackSpreader[T]) GetDownTracks() []T {
+	d.downTrackMu.RLock()
+	defer d.downTrackMu.RUnlock()
+	return d.downTracksShadow
+}
+
+func (d *DownTrackSpreader[T]) ResetAndGetDownTracks() []T {
+	d.downTrackMu.Lock()
+	defer d.downTrackMu.Unlock()
+
+	downTracks := d.downTracksShadow
+
+	d.downTracks = make(map[livekit.ParticipantID]T)
+	d.downTracksShadow = nil
+
+	return downTracks
+}
+
+func (d *DownTrackSpreader[T]) Store(sender T) {
+	d.downTrackMu.Lock()
+	defer d.downTrackMu.Unlock()
+
+	d.downTracks[sender.SubscriberID()] = sender
+	d.shadowDownTracks()
+}
+
+func (d *DownTrackSpreader[T]) Free(subscriberID livekit.ParticipantID) {
+	d.downTrackMu.Lock()
+	defer d.downTrackMu.Unlock()
+
+	delete(d.downTracks, subscriberID)
+	d.shadowDownTracks()
+}
+
+func (d *DownTrackSpreader[T]) HasDownTrack(subscriberID livekit.ParticipantID) bool {
+	d.downTrackMu.RLock()
+	defer d.downTrackMu.RUnlock()
+
+	_, ok := d.downTracks[subscriberID]
+	return ok
+}
+
+func (d *DownTrackSpreader[T]) Broadcast(writer func(T)) {
+	d.downTrackMu.RLock()
+	downTracks := d.downTracksShadow
+	threshold := uint64(d.params.Threshold)
+	d.downTrackMu.RUnlock()
+
+	if len(downTracks) == 0 {
+		return
+	}
+	if threshold == 0 {
+		threshold = 1000000
+	}
+
+	// 100µs is enough to amortize the overhead and provide sufficient load balancing.
+	// WriteRTP takes about 50µs on average, so we write to 2 down tracks per loop.
+	step := uint64(2)
+	utils.ParallelExec(downTracks, threshold, step, writer)
+}
+
+func (d *DownTrackSpreader[T]) DownTrackCount() int {
+	d.downTrackMu.RLock()
+	defer d.downTrackMu.RUnlock()
+	return len(d.downTracksShadow)
+}
+
+func (d *DownTrackSpreader[T]) shadowDownTracks() {
+	d.downTracksShadow = make([]T, 0, len(d.downTracks))
+	for _, dt := range d.downTracks {
+		d.downTracksShadow = append(d.downTracksShadow, dt)
+	}
+}
+
+func (d *DownTrackSpreader[T]) SetThreshold(threshold int) {
+	d.downTrackMu.Lock()
+	d.params.Threshold = threshold
+	d.downTrackMu.Unlock()
+}