Wayland: minimize surface commits and limit them to the main thread

Before of this patch, as explained in the usual
commented-wall-of-text-longer-than-the-actual-patch-itself™, due to the
multithreaded nature of the Wayland thread, it was possible to commit a
surface while the renderer was doing stuff, which was _very_ wrong.

Initially the consequences of such a sin weren't obvious but, now that
explicit synchronization is becoming more and more common, we can't
commit a buffer randomly without basically guaranteeing a nasty, nasty
crash (and we should have avoided commits altogether in the first place
to ensure atomic surface updates).

We now only trigger a commit _in the main thread_ when low processor usage
mode is on _and_ if we know that we won't be rendering anything as, due to
its intermittent nature, it makes "legacy" (pre xdg_wm_base v6) frame
callback based suspension quite annoying.

1 files changed, 4 insertions, 10 deletions

diff --git a/platform/linuxbsd/wayland/wayland_thread.cpp b/platform/linuxbsd/wayland/wayland_thread.cpp
index 63a8db07df..341cc517e3 100644
--- a/platform/linuxbsd/wayland/wayland_thread.cpp
+++ b/platform/linuxbsd/wayland/wayland_thread.cpp
@@ -968,7 +968,6 @@ void WaylandThread::_frame_wl_callback_on_done(void *data, struct wl_callback *w
 
 	ws->frame_callback = wl_surface_frame(ws->wl_surface),
 	wl_callback_add_listener(ws->frame_callback, &frame_wl_callback_listener, ws);
-	wl_surface_commit(ws->wl_surface);
 
 	if (ws->wl_surface && ws->buffer_scale_changed) {
 		// NOTE: We're only now setting the buffer scale as the idea is to get this
@@ -980,11 +979,6 @@ void WaylandThread::_frame_wl_callback_on_done(void *data, struct wl_callback *w
 		// rendering if needed.
 		wl_surface_set_buffer_scale(ws->wl_surface, window_state_get_preferred_buffer_scale(ws));
 	}
-
-	// NOTE: Remember to set here also other buffer-dependent states (e.g. opaque
-	// region) if used, to be as close as possible to an atomic surface update.
-	// Ideally we'd only have one surface commit, but it's not really doable given
-	// the current state of things.
 }
 
 void WaylandThread::_wl_surface_on_leave(void *data, struct wl_surface *wl_surface, struct wl_output *wl_output) {
@@ -3241,10 +3235,6 @@ void WaylandThread::window_create(DisplayServer::WindowID p_window_id, int p_wid
 	ws.frame_callback = wl_surface_frame(ws.wl_surface);
 	wl_callback_add_listener(ws.frame_callback, &frame_wl_callback_listener, &ws);
 
-	// NOTE: This commit is only called once to start the whole frame callback
-	// "loop".
-	wl_surface_commit(ws.wl_surface);
-
 	if (registry.xdg_exporter) {
 		ws.xdg_exported = zxdg_exporter_v1_export(registry.xdg_exporter, ws.wl_surface);
 		zxdg_exported_v1_add_listener(ws.xdg_exported, &xdg_exported_listener, &ws);
@@ -4120,6 +4110,10 @@ void WaylandThread::primary_set_text(const String &p_text) {
 	wl_display_roundtrip(wl_display);
 }
 
+void WaylandThread::commit_surfaces() {
+	wl_surface_commit(main_window.wl_surface);
+}
+
 void WaylandThread::set_frame() {
 	frame = true;
 }