[mutter] backend: Add 'prepare-shutdown' signal

[Marge Bot <marge-bot src gnome org>]

commit b31a639378b8c284096fc194d76b1847e665aa3d
Author: Jonas Ådahl <jadahl gmail com>
Date:   Wed Feb 3 10:59:06 2021 +0100

    backend: Add 'prepare-shutdown' signal
    
    This will be used to avoid doing various work when we're shutting down,
    e.g. react to changes triggering monitor reconfigurations.
    
    Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1698>

 src/backends/meta-backend-private.h |  2 ++
 src/backends/meta-backend.c         | 14 ++++++++++++++
 src/core/main.c                     |  4 ++++
 3 files changed, 20 insertions(+)
---
diff --git a/src/backends/meta-backend-private.h b/src/backends/meta-backend-private.h
index 3926a3c63a..0c328ffccd 100644
--- a/src/backends/meta-backend-private.h
+++ b/src/backends/meta-backend-private.h
@@ -110,6 +110,8 @@ void meta_init_backend (GType         backend_gtype,
                         const GValue *values);
 void meta_release_backend (void);
 
+void meta_backend_prepare_shutdown (MetaBackend *backend);
+
 #ifdef HAVE_WAYLAND
 MetaWaylandCompositor * meta_backend_get_wayland_compositor (MetaBackend *backend);
 
diff --git a/src/backends/meta-backend.c b/src/backends/meta-backend.c
index 6b2780eebd..e0249160db 100644
--- a/src/backends/meta-backend.c
+++ b/src/backends/meta-backend.c
@@ -94,6 +94,7 @@ enum
   LAST_DEVICE_CHANGED,
   LID_IS_CLOSED_CHANGED,
   GPU_ADDED,
+  PREPARE_SHUTDOWN,
 
   N_SIGNALS
 };
@@ -869,6 +870,13 @@ meta_backend_class_init (MetaBackendClass *klass)
                   0,
                   NULL, NULL, NULL,
                   G_TYPE_NONE, 1, META_TYPE_GPU);
+  signals[PREPARE_SHUTDOWN] =
+    g_signal_new ("prepare-shutdown",
+                  G_TYPE_FROM_CLASS (klass),
+                  G_SIGNAL_RUN_LAST,
+                  0,
+                  NULL, NULL, NULL,
+                  G_TYPE_NONE, 0);
 
   mutter_stage_views = g_getenv ("MUTTER_STAGE_VIEWS");
   stage_views_disabled = g_strcmp0 (mutter_stage_views, "0") == 0;
@@ -1485,6 +1493,12 @@ meta_release_backend (void)
   g_clear_object (&_backend);
 }
 
+void
+meta_backend_prepare_shutdown (MetaBackend *backend)
+{
+  g_signal_emit (backend, signals[PREPARE_SHUTDOWN], 0);
+}
+
 /**
  * meta_is_stage_views_enabled:
  *
diff --git a/src/core/main.c b/src/core/main.c
index a6c6fc8562..e204b68ffe 100644
--- a/src/core/main.c
+++ b/src/core/main.c
@@ -344,6 +344,10 @@ static void
 meta_finalize (void)
 {
   MetaDisplay *display = meta_get_display ();
+  MetaBackend *backend = meta_get_backend ();
+
+  if (backend)
+    meta_backend_prepare_shutdown (backend);
 
   if (display)
     meta_display_close (display,