[Bug 729760] appsrc: Changing caps and pushing buffers is not serialized

[GStreamer (bugzilla.gnome.org)]

https://bugzilla.gnome.org/show_bug.cgi?id=729760
  GStreamer | gst-plugins-base | git

--- Comment #18 from comicfans44 <comicfans44 at gmail.com> 2014-08-01 15:37:48 UTC ---
(In reply to comment #17)
> Review of attachment 282124 [details]:
> 
> ::: gst-libs/gst/app/gstappsrc.c
> @@ +537,3 @@
> +  while ((caps_or_buffer = g_queue_pop_head (priv->queue))) {
> +    if (caps_or_buffer) {
> +      gst_mini_object_unref (caps_or_buffer);
> 
> Can it ever be NULL?

the original implementation allows set NULL as new caps ,so the queued caps can
 also be NULL . that's also the reason I'm trying to use any caps instead of
NULL caps:)

> 
> @@ +1088,2 @@
>          /* Contiue checks caps and queue */
>          continue;
> 
> Here I was more thinking about a symmetric loop instead of this
> 
> while (!g_queue_is_empty (priv->queue)) {
>   obj = g_queue_pop_head (priv->queue);
> 
>   if (GST_IS_CAPS (obj)) {
>     caps = GST_CAPS (obj);
>     negotiate and stuff
>   } else if (GST_IS_BUFFER (obj)) {
>     buffer = GST_BUFFER (obj);
>     push buffer downstream and everything
>   }
>   gst_mini_object_unref (obj);
> }
seems more clear. BTW,it may be a "NULL" as caps in queue, this should be
considered

> 
> @@ +1190,3 @@
>    GST_DEBUG_OBJECT (appsrc, "setting caps to %" GST_PTR_FORMAT, caps);
> +
> +  caps_or_buffer = g_queue_peek_tail (priv->queue);
> 
> Why this complicated code? Just push the caps on the queue and handle them
> above :)

caller may set new caps multi times but didn't push any buffers between them,
my patch tried to skip these unnecessary re-negotitate . if every new caps
(even without buffer of this caps) event should be pushed downstream , I should
correct my patch.
> 
> @@ +1251,3 @@
> +  if ((caps = appsrc->priv->last_caps))
> +    gst_caps_ref (caps);
> +  GST_OBJECT_UNLOCK (appsrc);
> 
> Is the caps query now returning current_caps, while the caps property returns
> the last caps?
yes, basesrc_class->get_caps points to gst_app_src_internal_get_caps and return
 current_caps.  caps property use app_src_get_caps ,return last caps

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