[libcamera-devel] [PATCH v2 10/27] gst: libcamerasrc: Add a task for the streaming thread

[Nicolas Dufresne]

Use a GstTask as our internal streaming thread. Unlike GstBaseSrc, we
will be running a streaming thread at the element level rather than
per pad. This is needed to combine buffer request for multiple pads.

Signed-off-by: Nicolas Dufresne <nicolas.dufresne at collabora.com>
---
 src/gstreamer/gstlibcamerasrc.cpp | 49 +++++++++++++++++++++++++++++++
 1 file changed, 49 insertions(+)

diff --git a/src/gstreamer/gstlibcamerasrc.cpp b/src/gstreamer/gstlibcamerasrc.cpp
index 0c60478..53ece26 100644
--- a/src/gstreamer/gstlibcamerasrc.cpp
+++ b/src/gstreamer/gstlibcamerasrc.cpp
@@ -26,7 +26,11 @@ struct GstLibcameraSrcState {
 
 struct _GstLibcameraSrc {
 	GstElement parent;
+
+	GRecMutex stream_lock;
+	GstTask *task;
 	GstPad *srcpad;
+
 	gchar *camera_name;
 
 	GstLibcameraSrcState *state;
@@ -112,6 +116,30 @@ gst_libcamera_src_open(GstLibcameraSrc *self)
 	return true;
 }
 
+static void
+gst_libcamera_src_task_run(gpointer user_data)
+{
+	GstLibcameraSrc *self = GST_LIBCAMERA_SRC(user_data);
+
+	GST_DEBUG_OBJECT(self, "Streaming thread is now capturing");
+}
+
+static void
+gst_libcamera_src_task_enter(GstTask *task, GThread *thread, gpointer user_data)
+{
+	GstLibcameraSrc *self = GST_LIBCAMERA_SRC(user_data);
+
+	GST_DEBUG_OBJECT(self, "Streaming thread has started");
+}
+
+static void
+gst_libcamera_src_task_leave(GstTask *task, GThread *thread, gpointer user_data)
+{
+	GstLibcameraSrc *self = GST_LIBCAMERA_SRC(user_data);
+
+	GST_DEBUG_OBJECT(self, "Streaming thread is about to stop");
+}
+
 static void
 gst_libcamera_src_close(GstLibcameraSrc *self)
 {
@@ -182,9 +210,22 @@ gst_libcamera_src_change_state(GstElement *element, GstStateChange transition)
 			return GST_STATE_CHANGE_FAILURE;
 		break;
 	case GST_STATE_CHANGE_READY_TO_PAUSED:
+		/* This needs to be called after pads activation.*/
+		if (!gst_task_pause(self->task))
+			return GST_STATE_CHANGE_FAILURE;
+		ret = GST_STATE_CHANGE_NO_PREROLL;
+		break;
 	case GST_STATE_CHANGE_PLAYING_TO_PAUSED:
 		ret = GST_STATE_CHANGE_NO_PREROLL;
 		break;
+	case GST_STATE_CHANGE_PAUSED_TO_READY:
+		/* \todo this might requires some thread unblocking in the future
+		 * if the streaming thread starts doing any kind of blocking
+		 * operations. If this was the case, we would need to do so
+		 * before pad deactivation, so before chaining to the parent
+		 * change_state function. */
+		gst_task_join(self->task);
+		break;
 	case GST_STATE_CHANGE_READY_TO_NULL:
 		gst_libcamera_src_close(self);
 		break;
@@ -201,6 +242,8 @@ gst_libcamera_src_finalize(GObject *object)
 	GObjectClass *klass = G_OBJECT_CLASS(gst_libcamera_src_parent_class);
 	GstLibcameraSrc *self = GST_LIBCAMERA_SRC(object);
 
+	g_rec_mutex_clear(&self->stream_lock);
+	g_clear_object(&self->task);
 	g_free(self->camera_name);
 	delete self->state;
 
@@ -213,6 +256,12 @@ gst_libcamera_src_init(GstLibcameraSrc *self)
 	GstLibcameraSrcState *state = new GstLibcameraSrcState();
 	GstPadTemplate *templ = gst_element_get_pad_template(GST_ELEMENT(self), "src");
 
+	g_rec_mutex_init(&self->stream_lock);
+	self->task = gst_task_new(gst_libcamera_src_task_run, self, nullptr);
+	gst_task_set_enter_callback(self->task, gst_libcamera_src_task_enter, self, nullptr);
+	gst_task_set_leave_callback(self->task, gst_libcamera_src_task_leave, self, nullptr);
+	gst_task_set_lock(self->task, &self->stream_lock);
+
 	self->srcpad = gst_pad_new_from_template(templ, "src");
 	gst_element_add_pad(GST_ELEMENT(self), self->srcpad);
 	self->state = state;
-- 
2.24.1