[Bug 780128] New: vaapi: playbin3 doesn't work with vaapi elements on X11

[GStreamer (GNOME Bugzilla)]

https://bugzilla.gnome.org/show_bug.cgi?id=780128

            Bug ID: 780128
           Summary: vaapi: playbin3 doesn't work with vaapi elements on
                    X11
    Classification: Platform
           Product: GStreamer
           Version: git master
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: Normal
         Component: gstreamer-vaapi
          Assignee: gstreamer-bugs at lists.freedesktop.org
          Reporter: zzoon at igalia.com
        QA Contact: gstreamer-bugs at lists.freedesktop.org
                CC: bsreerenj at gmail.com, vjaquez at igalia.com
     GNOME version: ---

On the master, the following pipeline leads to deadlock with vaapi elements:
USE_PLAYBIN3=1 gst-play-1.0 xxx.mp4

though this is working:
gst-launch-1.0 filesrc location=xxx.mp4 ! decodebin3 ! vaapisink

This issue includes a couple of issues.

1. About sharing vaapidisplay between vaapi elements.
When we're using playbin(2) or decodebin2/3, vaapisink creates its own
vaapidisplay first, then shares it with other elements vaapidecoder and vpp.

But with playbin3, it's different.
vpp creates vaapidisplay and shares with vaapidecoder, not vaapisink since it's
not linked at this moment. Besides, playbin3 doesn't implement auto-query yet,
IIRC.
So vaapisink creates its own vaapidisplay. Finally, vaapisink get context
query, share and use the vaapidisplay of vpp/vaapidecoder.

Meanwhile, the shared vaapidisplay is vaapidisplayglx with glx context and
XDisplay from gst-gl.


2. XDisplay from gst-gl should be handeld by xcb probably.
Since the
commit(https://cgit.freedesktop.org/gstreamer/gst-plugins-bad/commit/gst-libs/gst/gl?id=4f6c226bd24ae3ef66bd8f4c17b001444c9b0bf1)
landed, This XDisplay can't work in our vaapiwindow_x11.

Eventually this causes this deadlock. In wait_event in vaapiwindow_x11.c,
it couldn't get the event MapNotify by this foreign XDisplay.

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