(3/3) Fix concurrency webcam windows (#684)

* Import wmcodecdsp and try to use their nv12 const

* Remove ifndef

* Enhance getCameraName function to retrieve friendly name from IPropertyBag, with fallback to display name. Update LDFLAGS in camera_windows.go to include oleaut32 library.

* Don't mistake label for friendly name

* Initialize COM for thread safety in Open and VideoRecord methods of camera_windows.go

* Refactor camera handling in camera_windows.go and camera_windows.cpp

- Introduced mutex for thread safety in camera struct to protect shared resources.
- Updated Open method to initialize done channel and manage camera state.
- Enhanced Close method to ensure proper cleanup and prevent double closing.
- Improved resolution listing logic in camera_windows.cpp by ensuring media types are freed correctly.
- Changed memory deletion from single to array deletion for camera properties.

* Fix issues post-rebase

* Refactor Close method

* Transfer golang buffer management to c to avoid gc

* Fix race condition in imageCallback by fixing unlock code location

pkg/driver/camera/camera_windows.cpp

@@ -253,7 +253,6 @@ int listResolution(camera* cam, const char** errstr)
   ICaptureGraphBuilder2* captureGraph = nullptr;
   IAMStreamConfig* config = nullptr;
   IPin* src = nullptr;
-  LPOLESTR name;
 
   if (!selectCamera(cam, &moniker, errstr))
   {
@@ -623,7 +622,7 @@ void freeCamera(camera* cam)
 
   if (cam->props)
   {
-    delete cam->props;
+    delete[] cam->props;
     cam->props = nullptr;
   }
 }

pkg/driver/camera/camera_windows.go

@@ -25,11 +25,17 @@ var (
 )
 
 type camera struct {
-	name  string
+	name string
-	cam   *C.camera
+	// mu protects the fields under as per the mutex hat convention.
-	ch    chan []byte
+	mu     sync.Mutex
-	buf   []byte
+	cam    *C.camera
-	bufGo []byte
+	closed bool
+	ch     chan []byte
+	done   chan struct{}
+
+	cbuf   unsafe.Pointer // C.malloc'd buffer for DirectShow writes
+	bufLen int            // byte length of cbuf
+	bufGo  []byte
 }
 
 func init() {
@@ -83,7 +89,20 @@ func DestroyObserver() error {
 }
 
 func (c *camera) Open() error {
+	// COM is per-thread on Windows. Go goroutines can run on any OS thread,
+	// so ensure COM is initialized on the current one before making COM calls.
+	C.CoInitializeEx(nil, C.COINIT_MULTITHREADED)
+
+	c.mu.Lock()
+	defer c.mu.Unlock()
+
+	if c.cam != nil {
+		return fmt.Errorf("camera already open")
+	}
+
 	c.ch = make(chan []byte)
+	c.done = make(chan struct{})
+	c.closed = false
 	c.cam = &C.camera{
 		name: C.CString(c.name),
 	}
@@ -91,6 +110,7 @@ func (c *camera) Open() error {
 	var errStr *C.char
 	if C.listResolution(c.cam, &errStr) != 0 {
 		C.free(unsafe.Pointer(c.cam.name))
+		c.cam = nil
 		return fmt.Errorf("failed to open device: %s", C.GoString(errStr))
 	}
 
@@ -101,36 +121,74 @@ func (c *camera) Open() error {
 func imageCallback(cam uintptr) {
 	callbacksMu.RLock()
 	cb, ok := callbacks[uintptr(unsafe.Pointer(cam))]
-	callbacksMu.RUnlock()
 	if !ok {
+		callbacksMu.RUnlock()
 		return
 	}
+	copy(cb.bufGo, unsafe.Slice((*byte)(cb.cbuf), cb.bufLen))
+	callbacksMu.RUnlock()
 
-	copy(cb.bufGo, cb.buf)
+	select {
-	cb.ch <- cb.bufGo
+	case cb.ch <- cb.bufGo:
+	case <-cb.done:
+	}
 }
 
 func (c *camera) Close() error {
-	callbacksMu.Lock()
+	c.mu.Lock()
-	key := uintptr(unsafe.Pointer(c.cam))
+	if c.closed {
-	if _, ok := callbacks[key]; ok {
+		c.mu.Unlock()
-		delete(callbacks, key)
+		return nil
 	}
-	callbacksMu.Unlock()
+	c.closed = true
-	close(c.ch)
+	cam := c.cam
+	c.cam = nil
+	cbuf := c.cbuf
+	c.cbuf = nil
+	done := c.done
+	ch := c.ch
+	c.mu.Unlock()
 
-	if c.cam != nil {
+	// Remove from callbacks map so no new imageCallback calls find this cam
-		C.free(unsafe.Pointer(c.cam.name))
+	callbacksMu.Lock()
-		C.freeCamera(c.cam)
+	delete(callbacks, uintptr(unsafe.Pointer(cam)))
-		c.cam = nil
+	callbacksMu.Unlock()
+
+	if done != nil {
+		close(done)
+	}
+
+	if cam != nil {
+		C.free(unsafe.Pointer(cam.name))
+		C.freeCamera(cam)
+	}
+
+	C.free(cbuf)
+
+	if ch != nil {
+		close(ch)
 	}
 	return nil
 }
 
 func (c *camera) VideoRecord(p prop.Media) (video.Reader, error) {
+	C.CoInitializeEx(nil, C.COINIT_MULTITHREADED)
+
+	c.mu.Lock()
+	defer c.mu.Unlock()
+
+	if c.cam == nil {
+		return nil, fmt.Errorf("camera not open")
+	}
+
 	nPix := p.Width * p.Height
-	c.buf = make([]byte, nPix*2)
+	bufSize := nPix * 2
-	c.bufGo = make([]byte, nPix*2)
+	c.cbuf = C.malloc(C.size_t(bufSize))
+	if c.cbuf == nil {
+		return nil, fmt.Errorf("failed to allocate frame buffer")
+	}
+	c.bufLen = bufSize
+	c.bufGo = make([]byte, bufSize)
 	c.cam.width = C.int(p.Width)
 	c.cam.height = C.int(p.Height)
 
@@ -141,10 +199,12 @@ func (c *camera) VideoRecord(p prop.Media) (video.Reader, error) {
 		c.cam.fcc = fourccYUY2
 	}
 
-	c.cam.buf = C.size_t(uintptr(unsafe.Pointer(&c.buf[0])))
+	c.cam.buf = C.size_t(uintptr(c.cbuf))
 
 	var errStr *C.char
 	if C.openCamera(c.cam, &errStr) != 0 {
+		C.free(c.cbuf)
+		c.cbuf = nil
 		return nil, fmt.Errorf("failed to open device: %s", C.GoString(errStr))
 	}
 
@@ -184,6 +244,11 @@ func (c *camera) VideoRecord(p prop.Media) (video.Reader, error) {
 }
 
 func (c *camera) Properties() []prop.Media {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	if c.cam == nil {
+		return nil
+	}
 	properties := []prop.Media{}
 	for i := 0; i < int(c.cam.numProps); i++ {
 		p := C.getProp(c.cam, C.int(i))