audio: Bug fix: Callback (audioprocess) can't treat goroutines (#119)

exp/audio/internal/audio.go

@@ -14,10 +14,6 @@
 
 package internal
 
-import (
-	"sync"
-)
-
 var audioEnabled = false
 
 const SampleRate = 44100
@@ -34,9 +30,6 @@ var MaxChannel = 32
 
 var channels = make([]*channel, MaxChannel)
 
-// NOTE: In GopherJS, sync.Mutex blocks a function and requires gopherjs:blocking comments.
-var channelsLock sync.Mutex
-
 func init() {
 	for i, _ := range channels {
 		channels[i] = &channel{
@@ -72,41 +65,42 @@ func channelAt(i int) *channel {
 }
 
 func Play(channel int, l []int16, r []int16) bool {
-	channelsLock.Lock()
-	defer channelsLock.Unlock()
+	result := false
+	withChannels(func() {
+		if !audioEnabled {
+			return
+		}
 
-	if !audioEnabled {
-		return false
-	}
-
-	if len(l) != len(r) {
-		panic("len(l) must equal to len(r)")
-	}
-	ch := channelAt(channel)
-	if ch == nil {
-		return false
-	}
-	ch.l = append(ch.l, make([]int16, ch.nextInsertionPosition-len(ch.l))...)
-	ch.r = append(ch.r, make([]int16, ch.nextInsertionPosition-len(ch.r))...)
-	ch.l = append(ch.l, l...)
-	ch.r = append(ch.r, r...)
-	return true
+		if len(l) != len(r) {
+			panic("len(l) must equal to len(r)")
+		}
+		ch := channelAt(channel)
+		if ch == nil {
+			return
+		}
+		ch.l = append(ch.l, make([]int16, ch.nextInsertionPosition-len(ch.l))...)
+		ch.r = append(ch.r, make([]int16, ch.nextInsertionPosition-len(ch.r))...)
+		ch.l = append(ch.l, l...)
+		ch.r = append(ch.r, r...)
+		result = true
+		return
+	})
+	return result
 }
 
 func Queue(channel int, l []int16, r []int16) {
-	channelsLock.Lock()
-	defer channelsLock.Unlock()
+	withChannels(func() {
+		if !audioEnabled {
+			return
+		}
 
-	if !audioEnabled {
-		return
-	}
-
-	if len(l) != len(r) {
-		panic("len(l) must equal to len(r)")
-	}
-	ch := channels[channel]
-	ch.l = append(ch.l, l...)
-	ch.r = append(ch.r, r...)
+		if len(l) != len(r) {
+			panic("len(l) must equal to len(r)")
+		}
+		ch := channels[channel]
+		ch.l = append(ch.l, l...)
+		ch.r = append(ch.r, r...)
+	})
 }
 
 func Tick() {
@@ -123,48 +117,51 @@ func min(a, b int) int {
 }
 
 func isChannelsEmpty() bool {
-	channelsLock.Lock()
-	defer channelsLock.Unlock()
-
-	if !audioEnabled {
-		return true
-	}
-
-	for _, ch := range channels {
-		if 0 < len(ch.l) {
-			return false
+	result := false
+	withChannels(func() {
+		if !audioEnabled {
+			result = true
+			return
 		}
-	}
-	return true
+
+		for _, ch := range channels {
+			if 0 < len(ch.l) {
+				return
+			}
+		}
+		result = true
+		return
+	})
+	return result
 }
 
 func loadChannelBuffer(channel int, bufferSize int) (l, r []int16) {
-	channelsLock.Lock()
-	defer channelsLock.Unlock()
+	withChannels(func() {
+		if !audioEnabled {
+			return
+		}
 
-	if !audioEnabled {
-		return nil, nil
-	}
-
-	ch := channels[channel]
-	length := min(len(ch.l), bufferSize)
-	inputL := make([]int16, length)
-	inputR := make([]int16, length)
-	copy(inputL, ch.l[:length])
-	copy(inputR, ch.r[:length])
-	ch.l = ch.l[length:]
-	ch.r = ch.r[length:]
-	ch.nextInsertionPosition -= min(bufferSize, ch.nextInsertionPosition)
-	return inputL, inputR
+		ch := channels[channel]
+		length := min(len(ch.l), bufferSize)
+		inputL := make([]int16, length)
+		inputR := make([]int16, length)
+		copy(inputL, ch.l[:length])
+		copy(inputR, ch.r[:length])
+		ch.l = ch.l[length:]
+		ch.r = ch.r[length:]
+		ch.nextInsertionPosition -= min(bufferSize, ch.nextInsertionPosition)
+		l, r = inputL, inputR
+	})
+	return
 }
 
 func IsPlaying(channel int) bool {
-	channelsLock.Lock()
-	defer channelsLock.Unlock()
-
-	if !audioEnabled {
-		return false
-	}
-
-	return isPlaying(channel)
+	result := false
+	withChannels(func() {
+		if !audioEnabled {
+			return
+		}
+		result = isPlaying(channel)
+	})
+	return result
 }

exp/audio/internal/audio_js.go

@@ -20,35 +20,41 @@ import (
 	"github.com/gopherjs/gopherjs/js"
 )
 
+func withChannels(f func()) {
+	f()
+}
+
 // Keep this so as not to be destroyed by GC.
-var nodes = []js.Object{}
-var context js.Object
+var (
+	nodes   = []js.Object{}
+	dummies = []js.Object{} // Dummy source nodes for iOS.
+	context js.Object
+)
 
 const bufferSize = 1024
 
 func audioProcess(channel int) func(e js.Object) {
 	return func(e js.Object) {
-		go func() {
-			defer func() {
-				currentPosition += bufferSize
-			}()
-
-			b := e.Get("outputBuffer")
-			l := b.Call("getChannelData", 0)
-			r := b.Call("getChannelData", 1)
-			inputL, inputR := loadChannelBuffer(channel, bufferSize)
-			const max = 1 << 15
-			for i := 0; i < len(inputL); i++ {
-				// TODO: Use copyToChannel?
-				if len(inputL) <= i {
-					l.SetIndex(i, 0)
-					r.SetIndex(i, 0)
-					continue
-				}
-				l.SetIndex(i, float64(inputL[i])/max)
-				r.SetIndex(i, float64(inputR[i])/max)
-			}
+		// Can't use 'go' here. Probably it may cause race conditions.
+		defer func() {
+			currentPosition += bufferSize
 		}()
+
+		b := e.Get("outputBuffer")
+		l := b.Call("getChannelData", 0)
+		r := b.Call("getChannelData", 1)
+		inputL, inputR := loadChannelBuffer(channel, bufferSize)
+		const max = 1 << 15
+		for i := 0; i < bufferSize; i++ {
+			// TODO: Use copyToChannel?
+			if len(inputL) <= i {
+				l.SetIndex(i, 0)
+				r.SetIndex(i, 0)
+				continue
+			}
+			l.SetIndex(i, float64(inputL[i])/max)
+			r.SetIndex(i, float64(inputR[i])/max)
+		}
 	}
 }
 
@@ -65,13 +71,18 @@ func initialize() {
 		node := context.Call("createScriptProcessor", bufferSize, 0, 2)
 		node.Call("addEventListener", "audioprocess", audioProcess(i))
 		nodes = append(nodes, node)
+
+		dummy := context.Call("createBufferSource")
+		dummies = append(dummies, dummy)
 	}
 	audioEnabled = true
 }
 
 func start() {
-	// TODO: For iOS, node should be connected with a buffer node.
-	for _, node := range nodes {
-		node.Call("connect", context.Get("destination"))
+	destination := context.Get("destination")
+	for i, node := range nodes {
+		dummy := dummies[i]
+		dummy.Call("connect", node)
+		node.Call("connect", destination)
 	}
 }

exp/audio/internal/audio_openal.go

@@ -23,9 +23,18 @@ import (
 	"github.com/timshannon/go-openal/openal"
 	"log"
 	"runtime"
+	"sync"
 	"time"
 )
 
+var channelsMutex = sync.Mutex{}
+
+func withChannels(f func()) {
+	channelsMutex.Lock()
+	defer channelsMutex.Unlock()
+	f()
+}
+
 func toBytesWithPadding(l, r []int16, size int) []byte {
 	if len(l) != len(r) {
 		panic("len(l) must equal to len(r)")