waylandsink: Avoid race condition on multi-threaded client

When waylandsink is used on some other thread than the main wayland
client thread, the waylandsink implementation is vulnerable to a

condition related to registry and surface events which handled in
seperated event queue.

The race that may happen is that after a proxy is created, but
before the queue is set, events meant to be emitted via the yet to

set queue may already have been queued on the wrong queue.

Wayland 1.11 introduced new API that allows creating a proxy
wrappper which can help to avoid this race condition.

1 files changed, 23 insertions, 16 deletions

diff --git a/ext/wayland/wlwindow.c b/ext/wayland/wlwindow.c
index 0c2e92937..e1efb75ed 100644
--- a/ext/wayland/wlwindow.c
+++ b/ext/wayland/wlwindow.c
@@ -92,6 +92,7 @@ gst_wl_window_finalize (GObject * gobject)
   if (self->video_viewport)
     wp_viewport_destroy (self->video_viewport);
 
+  wl_proxy_wrapper_destroy (self->video_surface_wrapper);
   wl_subsurface_destroy (self->video_subsurface);
   wl_surface_destroy (self->video_surface);
 
@@ -101,6 +102,7 @@ gst_wl_window_finalize (GObject * gobject)
   if (self->area_viewport)
     wp_viewport_destroy (self->area_viewport);
 
+  wl_proxy_wrapper_destroy (self->area_surface_wrapper);
   wl_surface_destroy (self->area_surface);
 
   g_clear_object (&self->display);
@@ -121,8 +123,13 @@ gst_wl_window_new_internal (GstWlDisplay * display, GMutex * render_lock)
   window->area_surface = wl_compositor_create_surface (display->compositor);
   window->video_surface = wl_compositor_create_surface (display->compositor);
 
-  wl_proxy_set_queue ((struct wl_proxy *) window->area_surface, display->queue);
-  wl_proxy_set_queue ((struct wl_proxy *) window->video_surface,
+  window->area_surface_wrapper = wl_proxy_create_wrapper (window->area_surface);
+  window->video_surface_wrapper =
+      wl_proxy_create_wrapper (window->video_surface);
+
+  wl_proxy_set_queue ((struct wl_proxy *) window->area_surface_wrapper,
+      display->queue);
+  wl_proxy_set_queue ((struct wl_proxy *) window->video_surface_wrapper,
       display->queue);
 
   /* embed video_surface in area_surface */
@@ -233,7 +240,7 @@ gst_wl_window_get_wl_surface (GstWlWindow * window)
 {
   g_return_val_if_fail (window != NULL, NULL);
 
-  return window->video_surface;
+  return window->video_surface_wrapper;
 }
 
 gboolean
@@ -267,8 +274,8 @@ gst_wl_window_resize_video_surface (GstWlWindow * window, gboolean commit)
   wl_subsurface_set_position (window->video_subsurface, res.x, res.y);
 
   if (commit) {
-    wl_surface_damage (window->video_surface, 0, 0, res.w, res.h);
-    wl_surface_commit (window->video_surface);
+    wl_surface_damage (window->video_surface_wrapper, 0, 0, res.w, res.h);
+    wl_surface_commit (window->video_surface_wrapper);
   }
 
   if (gst_wl_window_is_toplevel (window)) {
@@ -322,20 +329,20 @@ gst_wl_window_render (GstWlWindow * window, GstWlBuffer * buffer,
   }
 
   if (G_LIKELY (buffer))
-    gst_wl_buffer_attach (buffer, window->video_surface);
+    gst_wl_buffer_attach (buffer, window->video_surface_wrapper);
   else
-    wl_surface_attach (window->video_surface, NULL, 0, 0);
+    wl_surface_attach (window->video_surface_wrapper, NULL, 0, 0);
 
-  wl_surface_damage (window->video_surface, 0, 0, window->video_rectangle.w,
-      window->video_rectangle.h);
-  wl_surface_commit (window->video_surface);
+  wl_surface_damage (window->video_surface_wrapper, 0, 0,
+      window->video_rectangle.w, window->video_rectangle.h);
+  wl_surface_commit (window->video_surface_wrapper);
 
   if (G_UNLIKELY (info)) {
     /* commit also the parent (area_surface) in order to change
      * the position of the video_subsurface */
-    wl_surface_damage (window->area_surface, 0, 0, window->render_rectangle.w,
-        window->render_rectangle.h);
-    wl_surface_commit (window->area_surface);
+    wl_surface_damage (window->area_surface_wrapper, 0, 0,
+        window->render_rectangle.w, window->render_rectangle.h);
+    wl_surface_commit (window->area_surface_wrapper);
     wl_subsurface_set_desync (window->video_subsurface);
   }
 
@@ -385,7 +392,7 @@ gst_wl_window_update_borders (GstWlWindow * window)
       gst_wl_shm_memory_construct_wl_buffer (gst_buffer_peek_memory (buf, 0),
       window->display, &info);
   gwlbuf = gst_buffer_add_wl_buffer (buf, wlbuf, window->display);
-  gst_wl_buffer_attach (gwlbuf, window->area_surface);
+  gst_wl_buffer_attach (gwlbuf, window->area_surface_wrapper);
 
   /* at this point, the GstWlBuffer keeps the buffer
    * alive and will free it on wl_buffer::release */
@@ -419,8 +426,8 @@ gst_wl_window_set_render_rectangle (GstWlWindow * window, gint x, gint y,
     gst_wl_window_resize_video_surface (window, TRUE);
   }
 
-  wl_surface_damage (window->area_surface, 0, 0, w, h);
-  wl_surface_commit (window->area_surface);
+  wl_surface_damage (window->area_surface_wrapper, 0, 0, w, h);
+  wl_surface_commit (window->area_surface_wrapper);
 
   if (window->video_width != 0)
     wl_subsurface_set_desync (window->video_subsurface);