# HG changeset patch
# User Robert Mader <robert.mader@posteo.de>
# Date 1640087004 0
# Node ID 620f6d66f586a8f0efad2f58f7cb5db67f6b318b
# Parent  71184b9b6cb5f44580492b8f508b9363251111d3
Bug 1744896 - Create WaylandVsyncSource on window creation, r=stransky, a=dsmith

Previously we created the `WaylandVsyncSource` when calling
`WaylandStartVsync()` for the first time. Over a couple of refactorings,
this moved from `Create()` to happen much later in the process,
eventually racing with the content process which triggeres `VsyncParent`
to call `GetVsyncSource()`.
If the race went badly, `GetVsyncSource()` would return a `nullptr` and
the tab(s) in question would stick to the global software vsync source.

To avoid that, create the `WaylandVsyncSource` in `Create()` again.

Differential Revision: https://phabricator.services.mozilla.com/D134253

diff -up a/widget/gtk/nsWindow.cpp.1744896 b/widget/gtk/nsWindow.cpp
--- a/widget/gtk/nsWindow.cpp.1744896	2021-12-23 11:54:31.522539340 +0100
+++ b/widget/gtk/nsWindow.cpp	2021-12-23 11:55:56.070270174 +0100
@@ -5765,6 +5765,17 @@ nsresult nsWindow::Create(nsIWidget* aPa
       }
     }
 #endif
+#ifdef MOZ_WAYLAND
+  // Initialize the window specific VsyncSource early in order to avoid races
+  // with BrowserParent::UpdateVsyncParentVsyncSource().
+  // Only use for toplevel windows for now, see bug 1619246.
+  if (GdkIsWaylandDisplay() &&
+      StaticPrefs::widget_wayland_vsync_enabled_AtStartup() &&
+      mWindowType == eWindowType_toplevel) {
+    mWaylandVsyncSource = new WaylandVsyncSource();
+    MOZ_RELEASE_ASSERT(mWaylandVsyncSource);
+  }
+#endif
 
     // We create input contexts for all containers, except for
     // toplevel popup windows
@@ -6077,19 +6088,12 @@ void nsWindow::ResumeCompositorFromCompo
 
 void nsWindow::WaylandStartVsync() {
 #ifdef MOZ_WAYLAND
-  // only use for toplevel windows for now - see bug 1619246
-  if (!GdkIsWaylandDisplay() ||
-      !StaticPrefs::widget_wayland_vsync_enabled_AtStartup() ||
-      mWindowType != eWindowType_toplevel) {
+  if (!mWaylandVsyncSource) {
     return;
   }
 
   LOG("nsWindow::WaylandStartVsync() [%p]\n", (void*)this);
 
-  if (!mWaylandVsyncSource) {
-    mWaylandVsyncSource = new WaylandVsyncSource();
-  }
-
   WaylandVsyncSource::WaylandDisplay& display =
       static_cast<WaylandVsyncSource::WaylandDisplay&>(
           mWaylandVsyncSource->GetGlobalDisplay());