Reject renderer work after audio shutdown

fix.txt

@@ -85,7 +85,7 @@ Priority 1: transport, lifecycle, and correctness
    a cancellation context plus WaitGroup/done channel; serialize Start, Stop,
    reopen, and Destroy; wait before CaptureCloseDevice.
 
-10. Renderer can be used after it is closed
+[x] 10. Renderer can be used after it is closed
     Files: gumble/gumbleopenal/stream.go, gumble/gumble/audiolisteners.go
     Existing OnAudioStream goroutines can run cleanup after Destroy closes
     renderCh. Their final render call then panics sending on a closed channel.

gumble/gumbleopenal/stream.go

@@ -61,10 +61,12 @@ type Stream struct {
 	micVolume       atomic.Uint32 // float32 stored as bits
 	sourceStop      chan bool
 
-	deviceSink  *openal.Device
-	contextSink *openal.Context
-	renderCh    chan renderCommand
-	renderDone  chan struct{}
+	deviceSink   *openal.Device
+	contextSink  *openal.Context
+	renderMu     sync.RWMutex
+	renderCh     chan renderCommand
+	renderDone   chan struct{}
+	renderClosed bool
 
 	noiseProcessor      NoiseProcessor
 	noiseProcessorRight NoiseProcessor
@@ -159,8 +161,11 @@ func New(client *gumble.Client, inputDevice *string, outputDevice *string, test
 }
 
 func (s *Stream) startRenderer() {
+	s.renderMu.Lock()
+	s.renderClosed = false
 	s.renderCh = make(chan renderCommand)
 	s.renderDone = make(chan struct{})
+	s.renderMu.Unlock()
 	ready := make(chan struct{})
 	go func() {
 		runtime.LockOSThread()
@@ -177,11 +182,18 @@ func (s *Stream) startRenderer() {
 	<-ready
 }
 
-// render executes fn on the sole OS thread that owns the OpenAL context.
-func (s *Stream) render(fn func()) {
+// render executes fn on the sole OS thread that owns the OpenAL context. It
+// returns false after shutdown instead of sending to a closed renderer channel.
+func (s *Stream) render(fn func()) bool {
+	s.renderMu.RLock()
+	defer s.renderMu.RUnlock()
+	if s.renderClosed || s.renderCh == nil {
+		return false
+	}
 	command := renderCommand{fn: fn, done: make(chan struct{})}
 	s.renderCh <- command
 	<-command.done
+	return true
 }
 
 func (s *Stream) AttachStream(client *gumble.Client) {
@@ -296,7 +308,12 @@ func (s *Stream) Destroy() {
 				openal.NullContext.Activate()
 				s.contextSink.Destroy()
 			})
-			close(s.renderCh)
+			s.renderMu.Lock()
+			if !s.renderClosed {
+				close(s.renderCh)
+				s.renderClosed = true
+			}
+			s.renderMu.Unlock()
 			<-s.renderDone
 			s.contextSink = nil
 		}

gumble/gumbleopenal/stream_regression_test.go

@@ -0,0 +1,16 @@
+package gumbleopenal
+
+import "testing"
+
+// Regression: audio cleanup could send a final render command after Destroy
+// had closed renderCh, panicking instead of safely discarding that work.
+func TestRenderRejectsWorkAfterShutdown(t *testing.T) {
+	s := &Stream{renderClosed: true}
+	called := false
+	if s.render(func() { called = true }) {
+		t.Fatal("closed renderer accepted work")
+	}
+	if called {
+		t.Fatal("closed renderer executed work")
+	}
+}