xwayland: Allow setting up maintenance processes

This is made a signal, so the upper layers (read: gnome-shell) may
decide what to spawn, whether to add a GSetting, and whatnot. The
only signal argument contains the appropriate display to use for
this kind of setup.

data/org.gnome.mutter.gschema.xml.in

@@ -124,6 +124,8 @@
                                         real-time scheduling. The executable
                                         or user must have CAP_SYS_NICE.
                                         Requires a restart.
+        • “autostart-xwayland”        — initializes Xwayland lazily if there are
+                                        X11 clients. Requires restart.
       </description>
     </key>
 

src/backends/meta-settings-private.h

@@ -34,6 +34,7 @@ typedef enum _MetaExperimentalFeature
   META_EXPERIMENTAL_FEATURE_SCALE_MONITOR_FRAMEBUFFER = (1 << 0),
   META_EXPERIMENTAL_FEATURE_KMS_MODIFIERS  = (1 << 1),
   META_EXPERIMENTAL_FEATURE_RT_SCHEDULER = (1 << 2),
+  META_EXPERIMENTAL_FEATURE_AUTOSTART_XWAYLAND  = (1 << 3),
 } MetaExperimentalFeature;
 
 #define META_TYPE_SETTINGS (meta_settings_get_type ())

src/backends/meta-settings.c

@@ -266,6 +266,8 @@ experimental_features_handler (GVariant *features_variant,
         features |= META_EXPERIMENTAL_FEATURE_KMS_MODIFIERS;
       else if (g_str_equal (feature, "rt-scheduler"))
         features |= META_EXPERIMENTAL_FEATURE_RT_SCHEDULER;
+      else if (g_str_equal (feature, "autostart-xwayland"))
+        features |= META_EXPERIMENTAL_FEATURE_AUTOSTART_XWAYLAND;
       else
         g_info ("Unknown experimental feature '%s'\n", feature);
     }

src/compositor/compositor-private.h

@@ -74,4 +74,6 @@ MetaInhibitShortcutsDialog * meta_compositor_create_inhibit_shortcuts_dialog (Me
 
 void meta_compositor_locate_pointer (MetaCompositor *compositor);
 
+void meta_compositor_redirect_x11_windows (MetaCompositor *compositor);
+
 #endif /* META_COMPOSITOR_PRIVATE_H */

src/compositor/compositor.c

@@ -516,6 +516,15 @@ redirect_windows (MetaX11Display *x11_display)
     }
 }
 
+void
+meta_compositor_redirect_x11_windows (MetaCompositor *compositor)
+{
+  MetaDisplay *display = compositor->display;
+
+  if (display->x11_display)
+    redirect_windows (display->x11_display);
+}
+
 void
 meta_compositor_manage (MetaCompositor *compositor)
 {
@@ -595,8 +604,7 @@ meta_compositor_manage (MetaCompositor *compositor)
       compositor->have_x11_sync_object = meta_sync_ring_init (xdisplay);
     }
 
-  if (display->x11_display)
-    redirect_windows (display->x11_display);
+  meta_compositor_redirect_x11_windows (compositor);
 
   compositor->plugin_mgr = meta_plugin_manager_new (compositor);
 }

src/core/display-private.h

@@ -264,7 +264,7 @@ struct _MetaDisplayClass
 
 gboolean      meta_display_open                (void);
 
-void meta_display_manage_all_windows (MetaDisplay *display);
+void meta_display_manage_all_xwindows (MetaDisplay *display);
 void meta_display_unmanage_windows   (MetaDisplay *display,
                                       guint32      timestamp);
 

src/core/display.c

@@ -49,6 +49,7 @@
 #include "backends/x11/meta-backend-x11.h"
 #include "backends/x11/cm/meta-backend-x11-cm.h"
 #include "clutter/x11/clutter-x11.h"
+#include "compositor/compositor-private.h"
 #include "core/bell.h"
 #include "core/boxes-private.h"
 #include "core/display-private.h"
@@ -149,6 +150,7 @@ enum
   SHOWING_DESKTOP_CHANGED,
   RESTACKED,
   WORKAREAS_CHANGED,
+  INIT_XSERVER,
   LAST_SIGNAL
 };
 
@@ -479,6 +481,13 @@ meta_display_class_init (MetaDisplayClass *klass)
                   0, NULL, NULL, NULL,
                   G_TYPE_NONE, 0);
 
+  display_signals[INIT_XSERVER] =
+    g_signal_new ("init-xserver",
+                  G_TYPE_FROM_CLASS (klass),
+                  G_SIGNAL_RUN_LAST,
+                  0, NULL, NULL, NULL,
+                  G_TYPE_NONE, 1, G_TYPE_INT);
+
   g_object_class_install_property (object_class,
                                    PROP_FOCUS_WINDOW,
                                    g_param_spec_object ("focus-window",
@@ -643,10 +652,15 @@ meta_display_init_x11 (MetaDisplay  *display,
 
   display->x11_display = x11_display;
   g_signal_emit (display, display_signals[X11_DISPLAY_OPENED], 0);
-  meta_x11_display_create_guard_window (x11_display);
 
-  if (!display->display_opening)
-    meta_display_manage_all_windows (display);
+  if (meta_get_x11_display_policy () == META_DISPLAY_POLICY_ON_DEMAND)
+    {
+      meta_x11_display_create_guard_window (x11_display);
+      if (!display->display_opening)
+        meta_display_manage_all_xwindows (display);
+
+      meta_compositor_redirect_x11_windows (display->compositor);
+    }
 
   return TRUE;
 }
@@ -758,7 +772,7 @@ meta_display_open (void)
   display->selection = meta_selection_new (display);
   meta_clipboard_manager_init (display);
 
-  if (meta_should_autostart_x11_display ())
+  if (meta_get_x11_display_policy () == META_DISPLAY_POLICY_MANDATORY)
     {
       if (!meta_display_init_x11 (display, &error))
         g_error ("Failed to start Xwayland: %s", error->message);
@@ -797,7 +811,7 @@ meta_display_open (void)
    * we start out with no windows.
    */
   if (!meta_is_wayland_compositor ())
-    meta_display_manage_all_windows (display);
+    meta_display_manage_all_xwindows (display);
 
   if (old_active_xwindow != None)
     {
@@ -2448,7 +2462,7 @@ meta_resize_gravity_from_grab_op (MetaGrabOp op)
 }
 
 void
-meta_display_manage_all_windows (MetaDisplay *display)
+meta_display_manage_all_xwindows (MetaDisplay *display)
 {
   guint64 *_children;
   guint64 *children;
@@ -2462,7 +2476,8 @@ meta_display_manage_all_windows (MetaDisplay *display)
 
   for (i = 0; i < n_children; ++i)
     {
-      g_assert (META_STACK_ID_IS_X11 (children[i]));
+      if (!META_STACK_ID_IS_X11 (children[i]))
+        continue;
       meta_window_x11_new (display, children[i], TRUE,
                            META_COMP_EFFECT_NONE);
     }

src/core/frame.c

@@ -190,9 +190,14 @@ meta_window_destroy_frame (MetaWindow *window)
                   "Incrementing unmaps_pending on %s for reparent back to root\n", window->desc);
       window->unmaps_pending += 1;
     }
-  meta_stack_tracker_record_add (window->display->stack_tracker,
-                                 window->xwindow,
-                                 XNextRequest (x11_display->xdisplay));
+
+  if (!x11_display->closing)
+    {
+      meta_stack_tracker_record_add (window->display->stack_tracker,
+                                     window->xwindow,
+                                     XNextRequest (x11_display->xdisplay));
+    }
+
   XReparentWindow (x11_display->xdisplay,
                    window->xwindow,
                    x11_display->xroot,

src/core/keybindings.c

@@ -1570,6 +1570,8 @@ meta_window_grab_keys (MetaWindow  *window)
   MetaDisplay *display = window->display;
   MetaKeyBindingManager *keys = &display->key_binding_manager;
 
+  if (!meta_is_wayland_compositor ())
+    return;
   if (window->all_keys_grabbed)
     return;
 
@@ -1604,7 +1606,7 @@ meta_window_grab_keys (MetaWindow  *window)
 void
 meta_window_ungrab_keys (MetaWindow  *window)
 {
-  if (window->keys_grabbed)
+  if (!meta_is_wayland_compositor () && window->keys_grabbed)
     {
       MetaDisplay *display = window->display;
       MetaKeyBindingManager *keys = &display->key_binding_manager;
@@ -1663,7 +1665,11 @@ meta_display_grab_accelerator (MetaDisplay         *display,
       return META_KEYBINDING_ACTION_NONE;
     }
 
-  meta_change_keygrab (keys, display->x11_display->xroot, TRUE, &resolved_combo);
+  if (!meta_is_wayland_compositor ())
+    {
+      meta_change_keygrab (keys, display->x11_display->xroot,
+                           TRUE, &resolved_combo);
+    }
 
   grab = g_new0 (MetaKeyGrab, 1);
   grab->action = next_dynamic_keybinding_action ();
@@ -1709,8 +1715,11 @@ meta_display_ungrab_accelerator (MetaDisplay *display,
     {
       int i;
 
-      meta_change_keygrab (keys, display->x11_display->xroot,
-                           FALSE, &binding->resolved_combo);
+      if (!meta_is_wayland_compositor ())
+        {
+          meta_change_keygrab (keys, display->x11_display->xroot,
+                               FALSE, &binding->resolved_combo);
+        }
 
       for (i = 0; i < binding->resolved_combo.len; i++)
         {
@@ -1788,7 +1797,7 @@ meta_window_grab_all_keys (MetaWindow  *window,
                            guint32      timestamp)
 {
   Window grabwindow;
-  gboolean retval;
+  gboolean retval = TRUE;
 
   if (window->all_keys_grabbed)
     return FALSE;
@@ -1804,25 +1813,29 @@ meta_window_grab_all_keys (MetaWindow  *window,
               window->desc);
   meta_window_focus (window, timestamp);
 
-  grabwindow = meta_window_x11_get_toplevel_xwindow (window);
-
-  meta_topic (META_DEBUG_KEYBINDINGS,
-              "Grabbing all keys on window %s\n", window->desc);
-  retval = grab_keyboard (grabwindow, timestamp, XIGrabModeAsync);
-  if (retval)
+  if (!meta_is_wayland_compositor ())
     {
-      window->keys_grabbed = FALSE;
-      window->all_keys_grabbed = TRUE;
-      window->grab_on_frame = window->frame != NULL;
+      grabwindow = meta_window_x11_get_toplevel_xwindow (window);
+
+      meta_topic (META_DEBUG_KEYBINDINGS,
+                  "Grabbing all keys on window %s\n", window->desc);
+      retval = grab_keyboard (grabwindow, timestamp, XIGrabModeAsync);
+      if (retval)
+        {
+          window->keys_grabbed = FALSE;
+          window->all_keys_grabbed = TRUE;
+          window->grab_on_frame = window->frame != NULL;
+        }
     }
 
   return retval;
 }
 
 void
-meta_window_ungrab_all_keys (MetaWindow *window, guint32 timestamp)
+meta_window_ungrab_all_keys (MetaWindow *window,
+                             guint32     timestamp)
 {
-  if (window->all_keys_grabbed)
+  if (!meta_is_wayland_compositor () && window->all_keys_grabbed)
     {
       ungrab_keyboard (timestamp);
 

src/core/main-private.h

@@ -30,10 +30,17 @@ typedef enum _MetaCompositorType
   META_COMPOSITOR_TYPE_X11,
 } MetaCompositorType;
 
+typedef enum _MetaDisplayPolicy
+{
+  META_DISPLAY_POLICY_MANDATORY,
+  META_DISPLAY_POLICY_ON_DEMAND,
+  META_DISPLAY_POLICY_DISABLED,
+} MetaDisplayPolicy;
+
 META_EXPORT_TEST
 void meta_override_compositor_configuration (MetaCompositorType compositor_type,
                                              GType              backend_gtype);
 
-gboolean meta_should_autostart_x11_display (void);
+MetaDisplayPolicy meta_get_x11_display_policy (void);
 
 #endif /* META_MAIN_PRIVATE_H */

src/core/main.c

@@ -717,15 +717,27 @@ prefs_changed_callback (MetaPreference pref,
     }
 }
 
-gboolean
-meta_should_autostart_x11_display (void)
+MetaDisplayPolicy
+meta_get_x11_display_policy (void)
 {
   MetaBackend *backend = meta_get_backend ();
-  gboolean wants_x11 = TRUE;
+
+  if (META_IS_BACKEND_X11_CM (backend))
+    return META_DISPLAY_POLICY_MANDATORY;
 
 #ifdef HAVE_WAYLAND
-  wants_x11 = !opt_no_x11;
+  if (meta_is_wayland_compositor ())
+    {
+      MetaSettings *settings = meta_backend_get_settings (backend);
+
+      if (opt_no_x11)
+        return META_DISPLAY_POLICY_DISABLED;
+
+      if (meta_settings_is_experimental_feature_enabled (settings,
+                                                         META_EXPERIMENTAL_FEATURE_AUTOSTART_XWAYLAND))
+        return META_DISPLAY_POLICY_ON_DEMAND;
+    }
 #endif
 
-  return META_IS_BACKEND_X11_CM (backend) || wants_x11;
+  return META_DISPLAY_POLICY_MANDATORY;
 }

src/core/meta-launch-context.c

@@ -114,7 +114,7 @@ meta_launch_context_constructed (GObject *object)
 
   G_OBJECT_CLASS (meta_launch_context_parent_class)->constructed (object);
 
-  x11_display = getenv ("DISPLAY");
+  x11_display = meta_x11_get_display_name ();
   wayland_display = getenv ("WAYLAND_DISPLAY");
 
   if (x11_display)

src/core/stack-tracker.c

@@ -508,6 +508,42 @@ query_xserver_stack (MetaDisplay      *display,
   XFree (children);
 }
 
+static void
+drop_x11_windows (MetaDisplay      *display,
+                  MetaStackTracker *tracker)
+{
+  GArray *new_stack;
+  GList *l;
+  int i;
+
+  tracker->xserver_serial = 0;
+
+  new_stack = g_array_new (FALSE, FALSE, sizeof (guint64));
+
+  for (i = 0; i < tracker->verified_stack->len; i++)
+    {
+      guint64 window = g_array_index (tracker->verified_stack, guint64, i);
+
+      if (!META_STACK_ID_IS_X11 (window))
+        g_array_append_val (new_stack, window);
+    }
+
+  g_array_unref (tracker->verified_stack);
+  tracker->verified_stack = new_stack;
+  l = tracker->unverified_predictions->head;
+
+  while (l)
+    {
+      MetaStackOp *op = l->data;
+      GList *next = l->next;
+
+      if (META_STACK_ID_IS_X11 (op->any.window))
+        g_queue_remove (tracker->unverified_predictions, op);
+
+      l = next;
+    }
+}
+
 MetaStackTracker *
 meta_stack_tracker_new (MetaDisplay *display)
 {
@@ -523,6 +559,10 @@ meta_stack_tracker_new (MetaDisplay *display)
                     "x11-display-opened",
                     G_CALLBACK (query_xserver_stack),
                     tracker);
+  g_signal_connect (display,
+                    "x11-display-closing",
+                    G_CALLBACK (drop_x11_windows),
+                    tracker);
 
   meta_stack_tracker_dump (tracker);
 
@@ -546,6 +586,9 @@ meta_stack_tracker_free (MetaStackTracker *tracker)
   g_signal_handlers_disconnect_by_func (tracker->display,
                                         (gpointer)query_xserver_stack,
                                         tracker);
+  g_signal_handlers_disconnect_by_func (tracker->display,
+                                        drop_x11_windows,
+                                        tracker);
 
   g_free (tracker);
 }

src/wayland/meta-wayland-private.h

@@ -48,16 +48,26 @@ typedef struct
   char *lock_file;
   int abstract_fd;
   int unix_fd;
+  char *name;
+} MetaXWaylandConnection;
+
+typedef struct
+{
+  MetaXWaylandConnection private_connection;
+  MetaXWaylandConnection public_connection;
+
+  guint xserver_grace_period_id;
   struct wl_display *wayland_display;
   struct wl_client *client;
   struct wl_resource *xserver_resource;
-  char *display_name;
   char *auth_file;
 
   GCancellable *xserver_died_cancellable;
   GSubprocess *proc;
   GMainLoop *init_loop;
 
+  GList *x11_windows;
+
   MetaXWaylandDnd *dnd;
 } MetaXWaylandManager;
 

src/wayland/meta-wayland.c

@@ -418,9 +418,9 @@ meta_wayland_init (void)
   meta_wayland_eglstream_controller_init (compositor);
 #endif
 
-  if (meta_should_autostart_x11_display ())
+  if (meta_get_x11_display_policy () != META_DISPLAY_POLICY_DISABLED)
     {
-      if (!meta_xwayland_start (&compositor->xwayland_manager, compositor->wayland_display))
+      if (!meta_xwayland_init (&compositor->xwayland_manager, compositor->wayland_display))
         g_error ("Failed to start X Wayland");
     }
 
@@ -443,9 +443,9 @@ meta_wayland_init (void)
       compositor->display_name = g_strdup (display_name);
     }
 
-  if (meta_should_autostart_x11_display ())
+  if (meta_get_x11_display_policy () != META_DISPLAY_POLICY_DISABLED)
     {
-      set_gnome_env ("DISPLAY", meta_wayland_get_xwayland_display_name (compositor));
+      set_gnome_env ("DISPLAY", compositor->xwayland_manager.public_connection.name);
       set_gnome_env ("XAUTHORITY", meta_wayland_get_xwayland_auth_file (compositor));
     }
 
@@ -461,7 +461,7 @@ meta_wayland_get_wayland_display_name (MetaWaylandCompositor *compositor)
 const char *
 meta_wayland_get_xwayland_display_name (MetaWaylandCompositor *compositor)
 {
-  return compositor->xwayland_manager.display_name;
+  return compositor->xwayland_manager.private_connection.name;
 }
 
 void
@@ -471,7 +471,7 @@ meta_wayland_finalize (void)
 
   compositor = meta_wayland_compositor_get_default ();
 
-  meta_xwayland_stop (&compositor->xwayland_manager);
+  meta_xwayland_shutdown (&compositor->xwayland_manager);
   g_clear_pointer (&compositor->display_name, g_free);
 }
 

src/wayland/meta-xwayland-private.h

@@ -25,14 +25,14 @@
 #include "wayland/meta-wayland-private.h"
 
 gboolean
-meta_xwayland_start (MetaXWaylandManager *manager,
-                     struct wl_display   *display);
+meta_xwayland_init (MetaXWaylandManager *manager,
+		    struct wl_display   *display);
 
 void
 meta_xwayland_complete_init (MetaDisplay *display);
 
 void
-meta_xwayland_stop (MetaXWaylandManager *manager);
+meta_xwayland_shutdown (MetaXWaylandManager *manager);
 
 /* wl_data_device/X11 selection interoperation */
 void     meta_xwayland_init_dnd         (void);

src/wayland/meta-xwayland.c

@@ -41,6 +41,7 @@
 
 #include "compositor/meta-surface-actor-wayland.h"
 #include "compositor/meta-window-actor-private.h"
+#include "core/main-private.h"
 #include "meta/main.h"
 #include "wayland/meta-wayland-actor-surface.h"
 
@@ -70,6 +71,8 @@ G_DEFINE_TYPE (MetaWaylandSurfaceRoleXWayland,
 
 static int display_number_override = -1;
 
+static void meta_xwayland_stop_xserver (MetaXWaylandManager *manager);
+
 void
 meta_xwayland_associate_window_with_surface (MetaWindow          *window,
                                              MetaWaylandSurface  *surface)
@@ -368,24 +371,45 @@ xserver_died (GObject      *source,
       g_warning ("Failed to finish waiting for Xwayland: %s", error->message);
     }
   else if (!g_subprocess_get_successful (proc))
-    g_warning ("X Wayland crashed; exiting");
-  else
-    {
-      /* For now we simply abort if we see the server exit.
-       *
-       * In the future X will only be loaded lazily for legacy X support
-       * but for now it's a hard requirement. */
-      g_warning ("Spurious exit of X Wayland server");
-    }
+    g_warning ("X Wayland process exited");
 
-  meta_exit (META_EXIT_ERROR);
+  if (meta_get_x11_display_policy () == META_DISPLAY_POLICY_MANDATORY)
+    {
+      meta_exit (META_EXIT_ERROR);
+    }
+  else if (meta_get_x11_display_policy () == META_DISPLAY_POLICY_ON_DEMAND)
+    {
+      MetaWaylandCompositor *compositor = meta_wayland_compositor_get_default ();
+      MetaDisplay *display = meta_get_display ();
+
+      if (display->x11_display)
+        meta_display_shutdown_x11 (display);
+
+      if (!meta_xwayland_init (&compositor->xwayland_manager,
+                               compositor->wayland_display))
+        g_warning ("Failed to init X sockets");
+    }
+}
+
+static gboolean
+shutdown_xwayland_cb (gpointer data)
+{
+  MetaXWaylandManager *manager = data;
+
+  g_debug ("Shutting down Xwayland");
+  manager->xserver_grace_period_id = 0;
+  meta_display_shutdown_x11 (meta_get_display ());
+  meta_xwayland_stop_xserver (manager);
+  return G_SOURCE_REMOVE;
 }
 
 static int
 x_io_error (Display *display)
 {
   g_warning ("Connection to xwayland lost");
-  meta_exit (META_EXIT_ERROR);
+
+  if (meta_get_x11_display_policy () == META_DISPLAY_POLICY_MANDATORY)
+    meta_exit (META_EXIT_ERROR);
 
   return 0;
 }
@@ -397,7 +421,36 @@ meta_xwayland_override_display_number (int number)
 }
 
 static gboolean
-choose_xdisplay (MetaXWaylandManager *manager)
+open_display_sockets (MetaXWaylandManager *manager,
+                      int                  display_index,
+                      int                 *abstract_fd_out,
+                      int                 *unix_fd_out,
+                      gboolean            *fatal)
+{
+  int abstract_fd, unix_fd;
+
+  abstract_fd = bind_to_abstract_socket (display_index,
+                                         fatal);
+  if (abstract_fd < 0)
+    return FALSE;
+
+  unix_fd = bind_to_unix_socket (display_index);
+  if (unix_fd < 0)
+    {
+      *fatal = FALSE;
+      close (abstract_fd);
+      return FALSE;
+    }
+
+  *abstract_fd_out = abstract_fd;
+  *unix_fd_out = unix_fd;
+
+  return TRUE;
+}
+
+static gboolean
+choose_xdisplay (MetaXWaylandManager    *manager,
+                 MetaXWaylandConnection *connection)
 {
   int display = 0;
   char *lock_file = NULL;
@@ -417,8 +470,10 @@ choose_xdisplay (MetaXWaylandManager *manager)
           return FALSE;
         }
 
-      manager->abstract_fd = bind_to_abstract_socket (display, &fatal);
-      if (manager->abstract_fd < 0)
+      if (!open_display_sockets (manager, display,
+                                 &connection->abstract_fd,
+                                 &connection->unix_fd,
+                                 &fatal))
         {
           unlink (lock_file);
 
@@ -429,27 +484,18 @@ choose_xdisplay (MetaXWaylandManager *manager)
             }
           else
             {
-              g_warning ("Failed to bind abstract socket");
+              g_warning ("Failed to bind X11 socket");
               return FALSE;
             }
         }
 
-      manager->unix_fd = bind_to_unix_socket (display);
-      if (manager->unix_fd < 0)
-        {
-          unlink (lock_file);
-          close (manager->abstract_fd);
-          display++;
-          continue;
-        }
-
       break;
     }
   while (1);
 
-  manager->display_index = display;
-  manager->display_name = g_strdup_printf (":%d", manager->display_index);
-  manager->lock_file = lock_file;
+  connection->display_index = display;
+  connection->name = g_strdup_printf (":%d", connection->display_index);
+  connection->lock_file = lock_file;
 
   return TRUE;
 }
@@ -536,6 +582,7 @@ on_displayfd_ready (int          fd,
                     gpointer     user_data)
 {
   MetaXWaylandManager *manager = user_data;
+  MetaDisplay *display = meta_get_display ();
 
   /* The server writes its display name to the displayfd
    * socket when it's ready. We don't care about the data
@@ -543,11 +590,17 @@ on_displayfd_ready (int          fd,
    * that means it's ready. */
   xserver_finished_init (manager);
 
+  g_signal_emit_by_name (display, "init-xserver",
+                         manager->private_connection.display_index);
+
+  if (meta_get_x11_display_policy () == META_DISPLAY_POLICY_ON_DEMAND)
+    meta_display_init_x11 (display, NULL);
+
   return G_SOURCE_REMOVE;
 }
 
 static gboolean
-meta_xwayland_init_xserver (MetaXWaylandManager *manager)
+meta_xwayland_start_xserver (MetaXWaylandManager *manager)
 {
   int xwayland_client_fd[2];
   int displayfd[2];
@@ -581,14 +634,15 @@ meta_xwayland_init_xserver (MetaXWaylandManager *manager)
   launcher = g_subprocess_launcher_new (flags);
 
   g_subprocess_launcher_take_fd (launcher, xwayland_client_fd[1], 3);
-  g_subprocess_launcher_take_fd (launcher, manager->abstract_fd, 4);
-  g_subprocess_launcher_take_fd (launcher, manager->unix_fd, 5);
+  g_subprocess_launcher_take_fd (launcher, manager->public_connection.abstract_fd, 4);
+  g_subprocess_launcher_take_fd (launcher, manager->public_connection.unix_fd, 5);
   g_subprocess_launcher_take_fd (launcher, displayfd[1], 6);
+  g_subprocess_launcher_take_fd (launcher, manager->private_connection.abstract_fd, 7);
 
   g_subprocess_launcher_setenv (launcher, "WAYLAND_SOCKET", "3", TRUE);
 
   manager->proc = g_subprocess_launcher_spawn (launcher, &error,
-                                               XWAYLAND_PATH, manager->display_name,
+                                               XWAYLAND_PATH, manager->public_connection.name,
                                                "-rootless",
                                                "-noreset",
                                                "-accessx",
@@ -597,6 +651,7 @@ meta_xwayland_init_xserver (MetaXWaylandManager *manager)
                                                "-listen", "4",
                                                "-listen", "5",
                                                "-displayfd", "6",
+                                               "-initfd", "7",
                                                NULL);
   if (!manager->proc)
     {
@@ -620,30 +675,133 @@ meta_xwayland_init_xserver (MetaXWaylandManager *manager)
   return TRUE;
 }
 
-gboolean
-meta_xwayland_start (MetaXWaylandManager *manager,
-                     struct wl_display   *wl_display)
+static gboolean
+xdisplay_connection_activity_cb (gint         fd,
+                                 GIOCondition cond,
+                                 gpointer     user_data)
 {
-  if (!choose_xdisplay (manager))
-    return FALSE;
+  MetaXWaylandManager *manager = user_data;
+
+  if (!meta_xwayland_start_xserver (manager))
+    g_critical ("Could not start Xserver");
+
+  return G_SOURCE_REMOVE;
+}
+
+static void
+window_unmanaged_cb (MetaWindow          *window,
+                     MetaXWaylandManager *manager)
+{
+  manager->x11_windows = g_list_remove (manager->x11_windows, window);
+  g_signal_handlers_disconnect_by_func (window,
+                                        window_unmanaged_cb,
+                                        manager);
+  if (!manager->x11_windows)
+    {
+      g_debug ("All X11 windows gone, setting shutdown timeout");
+      manager->xserver_grace_period_id =
+        g_timeout_add_seconds (10, shutdown_xwayland_cb, manager);
+    }
+}
+
+static void
+window_created_cb (MetaDisplay         *display,
+                   MetaWindow          *window,
+                   MetaXWaylandManager *manager)
+{
+  if (window->xwindow &&
+      meta_window_get_client_pid (window) != getpid ())
+    {
+      manager->x11_windows = g_list_prepend (manager->x11_windows, window);
+      g_signal_connect (window, "unmanaged",
+                        G_CALLBACK (window_unmanaged_cb), manager);
+      if (manager->xserver_grace_period_id)
+        {
+          g_source_remove (manager->xserver_grace_period_id);
+          manager->xserver_grace_period_id = 0;
+        }
+    }
+}
+
+static void
+meta_xwayland_stop_xserver (MetaXWaylandManager *manager)
+{
+  if (manager->proc)
+    g_subprocess_send_signal (manager->proc, SIGTERM);
+  g_signal_handlers_disconnect_by_func (meta_get_display (),
+                                        window_created_cb,
+                                        manager);
+  g_clear_object (&manager->xserver_died_cancellable);
+  g_clear_object (&manager->proc);
+}
+
+gboolean
+meta_xwayland_init (MetaXWaylandManager *manager,
+                    struct wl_display   *wl_display)
+{
+  MetaDisplayPolicy policy;
+  gboolean fatal;
+
+  if (!manager->public_connection.name)
+    {
+      if (!choose_xdisplay (manager, &manager->public_connection))
+        return FALSE;
+      if (!choose_xdisplay (manager, &manager->private_connection))
+        return FALSE;
+    }
+  else
+    {
+      if (!open_display_sockets (manager,
+                                 manager->public_connection.display_index,
+                                 &manager->public_connection.abstract_fd,
+                                 &manager->public_connection.unix_fd,
+                                 &fatal))
+        return FALSE;
+
+      if (!open_display_sockets (manager,
+                                 manager->private_connection.display_index,
+                                 &manager->private_connection.abstract_fd,
+                                 &manager->private_connection.unix_fd,
+                                 &fatal))
+        return FALSE;
+    }
 
   if (!prepare_auth_file (manager))
     return FALSE;
 
   manager->wayland_display = wl_display;
-  return meta_xwayland_init_xserver (manager);
+  policy = meta_get_x11_display_policy ();
+
+  if (policy == META_DISPLAY_POLICY_MANDATORY)
+    {
+      return meta_xwayland_start_xserver (manager);
+    }
+  else if (policy == META_DISPLAY_POLICY_ON_DEMAND)
+    {
+      g_unix_fd_add (manager->public_connection.abstract_fd, G_IO_IN,
+                     xdisplay_connection_activity_cb, manager);
+      return TRUE;
+    }
+
+  return FALSE;
 }
 
 static void
 on_x11_display_closing (MetaDisplay *display)
 {
   meta_xwayland_shutdown_dnd ();
+  g_signal_handlers_disconnect_by_func (display,
+                                        on_x11_display_closing,
+                                        NULL);
 }
 
 /* To be called right after connecting */
 void
 meta_xwayland_complete_init (MetaDisplay *display)
 {
+  MetaWaylandCompositor *compositor = meta_wayland_compositor_get_default ();
+  MetaXWaylandManager *manager = &compositor->xwayland_manager;
+
   /* We install an X IO error handler in addition to the child watch,
      because after Xlib connects our child watch may not be called soon
      enough, and therefore we won't crash when X exits (and most important
@@ -654,31 +812,41 @@ meta_xwayland_complete_init (MetaDisplay *display)
   g_signal_connect (display, "x11-display-closing",
                     G_CALLBACK (on_x11_display_closing), NULL);
   meta_xwayland_init_dnd ();
+
+  g_signal_connect (meta_get_display (), "window-created",
+                    G_CALLBACK (window_created_cb), manager);
 }
 
 void
-meta_xwayland_stop (MetaXWaylandManager *manager)
+meta_xwayland_shutdown (MetaXWaylandManager *manager)
 {
   char path[256];
 
   g_cancellable_cancel (manager->xserver_died_cancellable);
-  g_clear_object (&manager->proc);
-  g_clear_object (&manager->xserver_died_cancellable);
 
-  snprintf (path, sizeof path, "/tmp/.X11-unix/X%d", manager->display_index);
+  snprintf (path, sizeof path, "/tmp/.X11-unix/X%d", manager->public_connection.display_index);
   unlink (path);
 
-  g_clear_pointer (&manager->display_name, g_free);
+  snprintf (path, sizeof path, "/tmp/.X11-unix/X%d", manager->private_connection.display_index);
+  unlink (path);
+
+  g_clear_pointer (&manager->public_connection.name, g_free);
+  g_clear_pointer (&manager->private_connection.name, g_free);
+  if (manager->public_connection.lock_file)
+    {
+      unlink (manager->public_connection.lock_file);
+      g_clear_pointer (&manager->public_connection.lock_file, g_free);
+    }
+  if (manager->private_connection.lock_file)
+    {
+      unlink (manager->private_connection.lock_file);
+      g_clear_pointer (&manager->private_connection.lock_file, g_free);
+    }
   if (manager->auth_file)
     {
       unlink (manager->auth_file);
       g_clear_pointer (&manager->auth_file, g_free);
     }
-  if (manager->lock_file)
-    {
-      unlink (manager->lock_file);
-      g_clear_pointer (&manager->lock_file, g_free);
-    }
 }
 
 static void

src/x11/meta-x11-display-private.h

@@ -144,6 +144,8 @@ struct _MetaX11Display
 
   guint keys_grabbed : 1;
 
+  guint closing : 1;
+
   /* we use property updates as sentinels for certain window focus events
    * to avoid some race conditions on EnterNotify events
    */
@@ -249,4 +251,6 @@ void meta_x11_display_set_input_focus (MetaX11Display *x11_display,
                                        Window          xwindow,
                                        guint32         timestamp);
 
+const gchar * meta_x11_get_display_name (void);
+
 #endif /* META_X11_DISPLAY_PRIVATE_H */

src/x11/meta-x11-display.c

@@ -129,17 +129,19 @@ meta_x11_display_dispose (GObject *object)
 {
   MetaX11Display *x11_display = META_X11_DISPLAY (object);
 
+  x11_display->closing = TRUE;
+
   meta_x11_startup_notification_release (x11_display);
 
   meta_prefs_remove_listener (prefs_changed_callback, x11_display);
 
   meta_x11_display_ungrab_keys (x11_display);
 
+  g_clear_object (&x11_display->x11_stack);
+
   meta_x11_selection_shutdown (x11_display);
   meta_x11_display_unmanage_windows (x11_display);
 
-  g_clear_object (&x11_display->x11_stack);
-
   if (x11_display->ui)
     {
       meta_ui_free (x11_display->ui);
@@ -182,21 +184,8 @@ meta_x11_display_dispose (GObject *object)
 
   if (x11_display->guard_window != None)
     {
-      MetaStackTracker *stack_tracker = x11_display->display->stack_tracker;
-
-      if (stack_tracker)
-        {
-          unsigned long serial;
-
-          serial = XNextRequest (x11_display->xdisplay);
-          meta_stack_tracker_record_remove (stack_tracker,
-                                            x11_display->guard_window,
-                                            serial);
-        }
-
       XUnmapWindow (x11_display->xdisplay, x11_display->guard_window);
       XDestroyWindow (x11_display->xdisplay, x11_display->guard_window);
-
       x11_display->guard_window = None;
     }
 
@@ -988,6 +977,25 @@ meta_set_gnome_wm_keybindings (const char *wm_keybindings)
   gnome_wm_keybindings = wm_keybindings;
 }
 
+const gchar *
+meta_x11_get_display_name (void)
+{
+#ifdef HAVE_WAYLAND
+  if (meta_is_wayland_compositor ())
+    {
+      MetaWaylandCompositor *compositor;
+
+      compositor = meta_wayland_compositor_get_default ();
+
+      return meta_wayland_get_xwayland_display_name (compositor);
+    }
+  else
+#endif
+    {
+      return g_getenv ("DISPLAY");
+    }
+}
+
 gboolean
 meta_x11_init_gdk_display (GError **error)
 {
@@ -996,7 +1004,7 @@ meta_x11_init_gdk_display (GError **error)
   const char *gdk_gl_env = NULL;
   Display *xdisplay;
 
-  xdisplay_name = g_getenv ("DISPLAY");
+  xdisplay_name = meta_x11_get_display_name ();
   if (!xdisplay_name)
     {
       g_set_error (error, G_IO_ERROR, G_IO_ERROR_FAILED,