gstreamer: Fix concurrent access issues to CameraManager

It's not allowed to have multiple instances of CameraManager. This
requirement is not easy for GStreamer were the device monitor and
the camerasrc, or two camerasrc instances don't usually have any
interaction between each other. Fix this by implementing a minimalist
singleton around CameraManager constructor and start()/stop()
operations.

Signed-off-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Tested-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

src/gstreamer/gstlibcamera-utils.cpp

@@ -178,3 +178,27 @@ gst_libcamera_resume_task(GstTask *task)
 		GST_TASK_SIGNAL(task);
 	}
 }
+
+G_LOCK_DEFINE_STATIC(cm_singleton_lock);
+std::weak_ptr<CameraManager> cm_singleton_ptr;
+
+std::shared_ptr<CameraManager>
+gst_libcamera_get_camera_mananger(int &ret)
+{
+	std::shared_ptr<CameraManager> cm;
+
+	G_LOCK(cm_singleton_lock);
+
+	cm = cm_singleton_ptr.lock();
+	if (!cm) {
+		cm = std::make_shared<CameraManager>();
+		cm_singleton_ptr = cm;
+		ret = cm->start();
+	} else {
+		ret = 0;
+	}
+
+	G_UNLOCK(cm_singleton_lock);
+
+	return cm;
+}

src/gstreamer/gstlibcamera-utils.h

@@ -9,16 +9,18 @@
 #ifndef __GST_LIBCAMERA_UTILS_H__
 #define __GST_LIBCAMERA_UTILS_H__
 
+#include <libcamera/camera_manager.h>
+#include <libcamera/stream.h>
+
 #include <gst/gst.h>
 #include <gst/video/video.h>
 
-#include <libcamera/stream.h>
-
 GstCaps *gst_libcamera_stream_formats_to_caps(const libcamera::StreamFormats &formats);
 GstCaps *gst_libcamera_stream_configuration_to_caps(const libcamera::StreamConfiguration &stream_cfg);
 void gst_libcamera_configure_stream_from_caps(libcamera::StreamConfiguration &stream_cfg,
 					      GstCaps *caps);
 void gst_libcamera_resume_task(GstTask *task);
+std::shared_ptr<libcamera::CameraManager> gst_libcamera_get_camera_mananger(int &ret);
 
 /**
  * \class GLibLocker

src/gstreamer/gstlibcameraprovider.cpp

@@ -158,7 +158,6 @@ gst_libcamera_device_new(const std::shared_ptr<Camera> &camera)
 
 struct _GstLibcameraProvider {
 	GstDeviceProvider parent;
-	CameraManager *cm;
 };
 
 G_DEFINE_TYPE_WITH_CODE(GstLibcameraProvider, gst_libcamera_provider,
@@ -170,7 +169,7 @@ static GList *
 gst_libcamera_provider_probe(GstDeviceProvider *provider)
 {
 	GstLibcameraProvider *self = GST_LIBCAMERA_PROVIDER(provider);
-	CameraManager *cm = self->cm;
+	std::shared_ptr<CameraManager> cm;
 	GList *devices = nullptr;
 	gint ret;
 
@@ -181,7 +180,7 @@ gst_libcamera_provider_probe(GstDeviceProvider *provider)
 	 * gains monitoring support. Meanwhile we need to cycle start()/stop()
 	 * to ensure every probe() calls return the latest list.
 	 */
-	ret = cm->start();
+	cm = gst_libcamera_get_camera_mananger(ret);
 	if (ret) {
 		GST_ERROR_OBJECT(self, "Failed to retrieve device list: %s",
 				 g_strerror(-ret));
@@ -194,8 +193,6 @@ gst_libcamera_provider_probe(GstDeviceProvider *provider)
 					g_object_ref_sink(gst_libcamera_device_new(camera)));
 	}
 
-	cm->stop();
-
 	return devices;
 }
 
@@ -204,31 +201,16 @@ gst_libcamera_provider_init(GstLibcameraProvider *self)
 {
 	GstDeviceProvider *provider = GST_DEVICE_PROVIDER(self);
 
-	self->cm = new CameraManager();
-
 	/* Avoid devices being duplicated. */
 	gst_device_provider_hide_provider(provider, "v4l2deviceprovider");
 }
 
-static void
-gst_libcamera_provider_finalize(GObject *object)
-{
-	GstLibcameraProvider *self = GST_LIBCAMERA_PROVIDER(object);
-	gpointer klass = gst_libcamera_provider_parent_class;
-
-	delete self->cm;
-
-	return G_OBJECT_CLASS(klass)->finalize(object);
-}
-
 static void
 gst_libcamera_provider_class_init(GstLibcameraProviderClass *klass)
 {
 	GstDeviceProviderClass *provider_class = GST_DEVICE_PROVIDER_CLASS(klass);
-	GObjectClass *object_class = G_OBJECT_CLASS(klass);
 
 	provider_class->probe = gst_libcamera_provider_probe;
-	object_class->finalize = gst_libcamera_provider_finalize;
 
 	gst_device_provider_class_set_metadata(provider_class,
 					       "libcamera Device Provider",

src/gstreamer/gstlibcamerasrc.cpp

@@ -108,7 +108,7 @@ GstBuffer *RequestWrap::detachBuffer(Stream *stream)
 struct GstLibcameraSrcState {
 	GstLibcameraSrc *src_;
 
-	std::unique_ptr<CameraManager> cm_;
+	std::shared_ptr<CameraManager> cm_;
 	std::shared_ptr<Camera> cam_;
 	std::unique_ptr<CameraConfiguration> config_;
 	std::vector<GstPad *> srcpads_;
@@ -202,13 +202,13 @@ GstLibcameraSrcState::requestCompleted(Request *request)
 static bool
 gst_libcamera_src_open(GstLibcameraSrc *self)
 {
-	std::unique_ptr<CameraManager> cm = std::make_unique<CameraManager>();
+	std::shared_ptr<CameraManager> cm;
 	std::shared_ptr<Camera> cam;
-	gint ret = 0;
+	gint ret;
 
 	GST_DEBUG_OBJECT(self, "Opening camera device ...");
 
-	ret = cm->start();
+	cm = gst_libcamera_get_camera_mananger(ret);
 	if (ret) {
 		GST_ELEMENT_ERROR(self, LIBRARY, INIT,
 				  ("Failed listing cameras."),
@@ -254,7 +254,7 @@ gst_libcamera_src_open(GstLibcameraSrc *self)
 	cam->requestCompleted.connect(self->state, &GstLibcameraSrcState::requestCompleted);
 
 	/* No need to lock here, we didn't start our threads yet. */
-	self->state->cm_ = std::move(cm);
+	self->state->cm_ = cm;
 	self->state->cam_ = cam;
 
 	return true;
@@ -521,7 +521,6 @@ gst_libcamera_src_close(GstLibcameraSrc *self)
 	}
 
 	state->cam_.reset();
-	state->cm_->stop();
 	state->cm_.reset();
 }