[libcamera-devel] [PATCH v2] gstreamer: Implement element EOS handling

[Nicolas Dufresne]

Le vendredi 10 novembre 2023 à 18:29 +0200, Laurent Pinchart via libcamera-devel
a écrit :
> Hi Jaslo,
> 
> Thank you for the patch.
> 
> On Fri, Nov 10, 2023 at 01:07:29PM +0100, Jaslo Ziska via libcamera-devel wrote:
> > Add a function for the send_event method which handles the GST_EVENT_EOS
> > event. This function will set an atomic to the received event and push
> > this EOS event to all source pads in the running task.
> > 
> > Also set the GST_ELEMENT_FLAG_SOURCE flag to identify libcamerasrc as a
> > source element which enables it to receive EOS events sent to the
> > (pipeline) bin containing it.
> > This in turn enables libcamerasrc to for example receive EOS events from
> > gst-launch-1.0 when using the -e flag.
> 
> You should reference https://bugs.libcamera.org/show_bug.cgi?id=91 with
> 
> Bug: https://bugs.libcamera.org/show_bug.cgi?id=91
> 
> Does this patch fix the bug completely or partially ? Nicolas mentioned
> in the review of v1 that there are two different EOS cases to consider,
> one related to stopping the pipeline with Ctrl-C, and the other one to
> downstream elements sending EOS. The commit message should explain that
> only the first case is addressed.
> 
> > Signed-off-by: Jaslo Ziska <jaslo at ziska.de>
> > Acked-by: Nicolas Dufresne <nicolas.dufresne at collabora.com>
> > ---
> > Use std::atomic<GstEvent *> instead of glib_atomic_int_* plus a seperate GstEvent pointer and add a commit message.
> > 
> >  src/gstreamer/gstlibcamerasrc.cpp | 37 ++++++++++++++++++++++++++++++-
> >  1 file changed, 36 insertions(+), 1 deletion(-)
> > 
> > diff --git a/src/gstreamer/gstlibcamerasrc.cpp b/src/gstreamer/gstlibcamerasrc.cpp
> > index 63d99571..8e197956 100644
> > --- a/src/gstreamer/gstlibcamerasrc.cpp
> > +++ b/src/gstreamer/gstlibcamerasrc.cpp
> > @@ -9,7 +9,6 @@
> >  /**
> >   * \todo The following is a list of items that needs implementation in the GStreamer plugin
> >   *  - Implement GstElement::send_event
> > - *    + Allowing application to send EOS
> >   *    + Allowing application to use FLUSH/FLUSH_STOP
> >   *    + Prevent the main thread from accessing streaming thread
> >   *  - Implement renegotiation (even if slow)
> > @@ -29,6 +28,7 @@
> > 
> >  #include "gstlibcamerasrc.h"
> > 
> > +#include <atomic>
> >  #include <queue>
> >  #include <vector>
> > 
> > @@ -144,6 +144,8 @@ struct _GstLibcameraSrc {
> >  	gchar *camera_name;
> >  	controls::AfModeEnum auto_focus_mode = controls::AfModeManual;
> > 
> > +	std::atomic<GstEvent *> pending_eos;
> > +
> >  	GstLibcameraSrcState *state;
> >  	GstLibcameraAllocator *allocator;
> >  	GstFlowCombiner *flow_combiner;
> > @@ -397,6 +399,14 @@ gst_libcamera_src_task_run(gpointer user_data)
> > 
> >  	bool doResume = false;
> > 
> > +	if (GstEvent *event = self->pending_eos.exchange(nullptr)) {
> 
> I don't think we ever declare variables in if () statements in
> libcamera, you may want to write this as
> 
> 	GstEvent *event = self->pending_eos.exchange(nullptr);
> 	if (event) {

Personally I like te in-scope declaration better. An you can improve it with:

	if (g_autoptr(GstEvent) event = ...)

> 
> > +		for (GstPad *srcpad : state->srcpads_)
> > +			gst_pad_push_event(srcpad, gst_event_ref(event));
> > +		gst_event_unref(event);

Witch let you drop this.

> > +
> > +		return;
> > +	}
> > +
> >  	/*
> >  	 * Create and queue one request. If no buffers are available the
> >  	 * function returns -ENOBUFS, which we ignore here as that's not a
> > @@ -747,6 +757,28 @@ gst_libcamera_src_change_state(GstElement *element, GstStateChange transition)
> >  	return ret;
> >  }
> > 
> > +static gboolean
> > +gst_libcamera_src_send_event(GstElement *element, GstEvent *event)
> > +{
> > +	GstLibcameraSrc *self = GST_LIBCAMERA_SRC(element);
> > +	gboolean ret = FALSE;
> > +
> > +	switch (GST_EVENT_TYPE(event)) {
> > +	case GST_EVENT_EOS: {
> > +		if (GstEvent *old_event = self->pending_eos.exchange(event))
> > +			gst_event_unref(old_event);
> 
> s/old_event/oldEvent/
> 
> gst_event_unref() includes a null check, so you could simplify this to

Please don't, there is a run-time check, but it can be compiled out. You will
always get an error message (and a crashed if you decided to drop run-time
checks, which are just protections).

> 
> 		GstEvent *oldEvent = self->pending_eos.exchange(event))
> 		gst_event_unref(oldEvent);
> 
> > +
> > +		ret = TRUE;
> > +		break;
> > +	}
> > +	default:
> > +		gst_event_unref(event);
> > +		break;
> > +	}
> > +
> > +	return ret;
> > +}
> > +
> >  static void
> >  gst_libcamera_src_finalize(GObject *object)
> >  {
> > @@ -779,6 +811,8 @@ gst_libcamera_src_init(GstLibcameraSrc *self)
> >  	state->srcpads_.push_back(gst_pad_new_from_template(templ, "src"));
> >  	gst_element_add_pad(GST_ELEMENT(self), state->srcpads_.back());
> > 
> > +	GST_OBJECT_FLAG_SET(self, GST_ELEMENT_FLAG_SOURCE);
> > +
> >  	/* C-style friend. */
> >  	state->src_ = self;
> >  	self->state = state;
> > @@ -844,6 +878,7 @@ gst_libcamera_src_class_init(GstLibcameraSrcClass *klass)
> >  	element_class->request_new_pad = gst_libcamera_src_request_new_pad;
> >  	element_class->release_pad = gst_libcamera_src_release_pad;
> >  	element_class->change_state = gst_libcamera_src_change_state;
> > +	element_class->send_event = gst_libcamera_src_send_event;
> > 
> >  	gst_element_class_set_metadata(element_class,
> >  				       "libcamera Source", "Source/Video",
>