backends/native: Add input thread inside MetaSeatImpl

This (now) doesn't change anything in regards to the API that the UI
thread should access from the MetaSeatImpl. The MetaInputDeviceNative,
MetaInputSettings and MetaKeymap objects are now considered owned by
the input thread, as well as all of libinput objects.

The MetaEventSource now dispatches events in a GMainContext that is
the thread default to this thread, and all UI-thread-accessible API
(seat and virtual input device API) will be handled in a serialized
manner by that same input thread.

The MetaSeatImpl itself is still considered to be owned by the caller
thread, and all the signals that this object emits will be emitted in
the GMainContext that is default at the time of calling
meta_seat_impl_new().

The MetaInputSettings configuration changes will likewise be handled
in the input thread, close to libinput devices.

https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1403

src/backends/native/meta-seat-impl.c

@@ -118,7 +118,11 @@ enum
 
 static guint signals[N_SIGNALS] = { 0 };
 
-G_DEFINE_TYPE (MetaSeatImpl, meta_seat_impl, G_TYPE_OBJECT)
+static void meta_seat_impl_initable_iface_init (GInitableIface *iface);
+
+G_DEFINE_TYPE_WITH_CODE (MetaSeatImpl, meta_seat_impl, G_TYPE_OBJECT,
+                         G_IMPLEMENT_INTERFACE (G_TYPE_INITABLE,
+                                                meta_seat_impl_initable_iface_init))
 
 static void process_events (MetaSeatImpl *seat);
 void meta_seat_impl_constrain_pointer (MetaSeatImpl       *seat,
@@ -314,6 +318,50 @@ update_button_count (MetaSeatImpl *seat,
     }
 }
 
+typedef struct
+{
+  MetaSeatImpl *seat;
+  guint signal_id;
+  guint arg1;
+  guint arg2;
+} MetaSeatSignalData;
+
+static gboolean
+emit_signal_main (MetaSeatSignalData *data)
+{
+  g_signal_emit (data->seat,
+                 data->signal_id,
+                 0,
+                 data->arg1,
+                 data->arg2);
+  return G_SOURCE_REMOVE;
+}
+
+static void
+emit_signal (MetaSeatImpl *seat,
+             guint         signal_id,
+             guint         arg1,
+             guint         arg2)
+{
+  MetaSeatSignalData *emit_signal_data;
+  GSource *source;
+
+  emit_signal_data = g_new0 (MetaSeatSignalData, 1);
+  emit_signal_data->seat = seat;
+  emit_signal_data->signal_id = signal_id;
+  emit_signal_data->arg1 = arg1;
+  emit_signal_data->arg2 = arg2;
+
+  source = g_idle_source_new ();
+  g_source_set_priority (source, G_PRIORITY_HIGH);
+  g_source_set_callback (source,
+                         (GSourceFunc) emit_signal_main,
+                         emit_signal_data,
+                         g_free);
+
+  g_source_attach (source, seat->caller_context);
+}
+
 void
 meta_seat_impl_notify_key (MetaSeatImpl       *seat,
                            ClutterInputDevice *device,
@@ -364,7 +412,7 @@ meta_seat_impl_notify_key (MetaSeatImpl       *seat,
 
   if (update_keys && (changed_state & XKB_STATE_LEDS))
     {
-      g_signal_emit (seat, signals[MODS_STATE_CHANGED], 0);
+      emit_signal (seat, signals[MODS_STATE_CHANGED], 0, 0);
       meta_seat_impl_sync_leds (seat);
       meta_input_device_native_a11y_maybe_notify_toggle_keys (META_INPUT_DEVICE_NATIVE (seat->core_keyboard));
     }
@@ -873,26 +921,13 @@ meta_seat_impl_notify_touch_event (MetaSeatImpl       *seat,
 /*
  * MetaEventSource for reading input devices
  */
-static gboolean
-meta_event_prepare (GSource *source,
-                    gint    *timeout)
-{
-  gboolean retval;
-
-  *timeout = -1;
-  retval = clutter_events_pending ();
-
-  return retval;
-}
-
 static gboolean
 meta_event_check (GSource *source)
 {
   MetaEventSource *event_source = (MetaEventSource *) source;
   gboolean retval;
 
-  retval = ((event_source->event_poll_fd.revents & G_IO_IN) ||
+  retval = !!(event_source->event_poll_fd.revents & G_IO_IN);
-            clutter_events_pending ());
 
   return retval;
 }
@@ -1372,19 +1407,13 @@ meta_event_dispatch (GSource     *g_source,
 
   seat = source->seat_impl;
 
-  /* Don't queue more events if we haven't finished handling the previous batch
-   */
-  if (clutter_events_pending ())
-    goto queue_event;
-
   dispatch_libinput (seat);
 
- queue_event:
-
   return TRUE;
 }
+
 static GSourceFuncs event_funcs = {
-  meta_event_prepare,
+  NULL,
   meta_event_check,
   meta_event_dispatch,
   NULL
@@ -1411,7 +1440,7 @@ meta_event_source_new (MetaSeatImpl *seat)
   g_source_set_priority (source, CLUTTER_PRIORITY_EVENTS);
   g_source_add_poll (source, &event_source->event_poll_fd);
   g_source_set_can_recurse (source, TRUE);
-  g_source_attach (source, NULL);
+  g_source_attach (source, seat->input_context);
 
   return event_source;
 }
@@ -1467,7 +1496,7 @@ update_touch_mode (MetaSeatImpl *seat)
   if (seat->touch_mode != touch_mode)
     {
       seat->touch_mode = touch_mode;
-      g_signal_emit (seat, signals[TOUCH_MODE], 0, touch_mode);
+      emit_signal (seat, signals[TOUCH_MODE], touch_mode, 0);
     }
 }
 
@@ -2466,36 +2495,21 @@ static const struct libinput_interface libinput_interface = {
   close_restricted
 };
 
-static void
+static gpointer
-meta_seat_impl_constructed (GObject *object)
+input_thread (MetaSeatImpl *seat)
 {
-  MetaSeatImpl *seat = META_SEAT_IMPL (object);
-  ClutterInputDevice *device;
   MetaEventSource *source;
   struct udev *udev;
   struct xkb_keymap *xkb_keymap;
 
-  g_rw_lock_writer_lock (&seat->state_lock);
+  g_main_context_push_thread_default (seat->input_context);
-
-  device = meta_input_device_native_new_virtual (
-      seat, CLUTTER_POINTER_DEVICE,
-      CLUTTER_INPUT_MODE_MASTER);
-  seat->pointer_x = INITIAL_POINTER_X;
-  seat->pointer_y = INITIAL_POINTER_Y;
-  meta_input_device_native_update_coords (META_INPUT_DEVICE_NATIVE (device),
-                                          seat->pointer_x, seat->pointer_y);
-  seat->core_pointer = device;
-
-  device = meta_input_device_native_new_virtual (
-      seat, CLUTTER_KEYBOARD_DEVICE,
-      CLUTTER_INPUT_MODE_MASTER);
-  seat->core_keyboard = device;
 
   udev = udev_new ();
   if (G_UNLIKELY (udev == NULL))
     {
       g_warning ("Failed to create udev object");
-      return;
+      seat->input_thread_initialized = TRUE;
+      return NULL;
     }
 
   seat->libinput = libinput_udev_create_context (&libinput_interface,
@@ -2503,7 +2517,8 @@ meta_seat_impl_constructed (GObject *object)
   if (seat->libinput == NULL)
     {
       g_critical ("Failed to create the libinput object.");
-      return;
+      seat->input_thread_initialized = TRUE;
+      return NULL;
     }
 
   if (libinput_udev_assign_seat (seat->libinput, seat->seat_id) == -1)
@@ -2511,19 +2526,20 @@ meta_seat_impl_constructed (GObject *object)
       g_critical ("Failed to assign a seat to the libinput object.");
       libinput_unref (seat->libinput);
       seat->libinput = NULL;
-      return;
+      seat->input_thread_initialized = TRUE;
+      return NULL;
     }
 
   udev_unref (udev);
 
   seat->input_settings = meta_input_settings_native_new (seat);
 
-  seat->udev_client = g_udev_client_new ((const gchar *[]) { "input", NULL });
-
   source = meta_event_source_new (seat);
   seat->event_source = source;
 
   seat->keymap = g_object_new (META_TYPE_KEYMAP_NATIVE, NULL);
+
+  g_rw_lock_writer_lock (&seat->state_lock);
   xkb_keymap = meta_keymap_native_get_keyboard_map (seat->keymap);
 
   if (xkb_keymap)
@@ -2543,6 +2559,63 @@ meta_seat_impl_constructed (GObject *object)
   seat->has_touchscreen = has_touchscreen (seat);
   update_touch_mode (seat);
 
+  seat->input_thread_initialized = TRUE;
+
+  seat->input_loop = g_main_loop_new (seat->input_context, FALSE);
+  g_main_loop_run (seat->input_loop);
+  g_main_loop_unref (seat->input_loop);
+
+  g_main_context_pop_thread_default (seat->input_context);
+
+  return NULL;
+}
+
+static gboolean
+meta_seat_impl_initable_init (GInitable     *initable,
+                              GCancellable  *cancellable,
+                              GError       **error)
+{
+  MetaSeatImpl *seat = META_SEAT_IMPL (initable);
+
+  seat->input_context = g_main_context_new ();
+  seat->caller_context = g_main_context_ref_thread_default ();
+
+  seat->input_thread =
+    g_thread_try_new ("Mutter Input Thread",
+                      (GThreadFunc) input_thread,
+                      initable,
+                      error);
+  if (!seat->input_thread)
+    return FALSE;
+
+  while (!seat->input_thread_initialized)
+    g_usleep (100);
+
+  return TRUE;
+}
+
+static void
+meta_seat_impl_constructed (GObject *object)
+{
+  MetaSeatImpl *seat = META_SEAT_IMPL (object);
+  ClutterInputDevice *device;
+
+  device = meta_input_device_native_new_virtual (
+      seat, CLUTTER_POINTER_DEVICE,
+      CLUTTER_INPUT_MODE_MASTER);
+  seat->pointer_x = INITIAL_POINTER_X;
+  seat->pointer_y = INITIAL_POINTER_Y;
+  meta_input_device_native_update_coords (META_INPUT_DEVICE_NATIVE (device),
+                                          seat->pointer_x, seat->pointer_y);
+  seat->core_pointer = device;
+
+  device = meta_input_device_native_new_virtual (
+      seat, CLUTTER_KEYBOARD_DEVICE,
+      CLUTTER_INPUT_MODE_MASTER);
+  seat->core_keyboard = device;
+
+  seat->udev_client = g_udev_client_new ((const gchar *[]) { "input", NULL });
+
   if (G_OBJECT_CLASS (meta_seat_impl_parent_class)->constructed)
     G_OBJECT_CLASS (meta_seat_impl_parent_class)->constructed (object);
 }
@@ -2609,6 +2682,9 @@ meta_seat_impl_finalize (GObject *object)
   MetaSeatImpl *seat = META_SEAT_IMPL (object);
   GSList *iter;
 
+  g_main_loop_quit (seat->input_loop);
+  g_thread_join (seat->input_thread);
+
   for (iter = seat->devices; iter; iter = g_slist_next (iter))
     {
       ClutterInputDevice *device = iter->data;
@@ -2769,6 +2845,12 @@ meta_seat_impl_query_state (MetaSeatImpl         *seat,
   return retval;
 }
 
+static void
+meta_seat_impl_initable_iface_init (GInitableIface *iface)
+{
+  iface->init = meta_seat_impl_initable_init;
+}
+
 static void
 meta_seat_impl_class_init (MetaSeatImplClass *klass)
 {
@@ -3304,10 +3386,11 @@ MetaSeatImpl *
 meta_seat_impl_new (MetaSeatNative *seat,
                     const gchar    *seat_id)
 {
-  return g_object_new (META_TYPE_SEAT_IMPL,
+  return g_initable_new (META_TYPE_SEAT_IMPL,
-                       "seat", seat,
+                         NULL, NULL,
-                       "seat-id", seat_id,
+                         "seat", seat,
-                       NULL);
+                         "seat-id", seat_id,
+                         NULL);
 }
 
 void
@@ -3320,8 +3403,7 @@ meta_seat_impl_notify_kbd_a11y_flags_changed (MetaSeatImpl          *impl,
   input_settings = impl->input_settings;
   meta_input_settings_notify_kbd_a11y_change (input_settings,
                                               new_flags, what_changed);
-  g_signal_emit (impl, signals[KBD_A11Y_FLAGS_CHANGED], 0,
+  emit_signal (impl, signals[KBD_A11Y_FLAGS_CHANGED], new_flags, what_changed);
-                 new_flags, what_changed);
 }
 
 void
@@ -3329,14 +3411,14 @@ meta_seat_impl_notify_kbd_a11y_mods_state_changed (MetaSeatImpl   *impl,
                                                    xkb_mod_mask_t  new_latched_mods,
                                                    xkb_mod_mask_t  new_locked_mods)
 {
-  g_signal_emit (impl, signals[KBD_A11Y_MODS_STATE_CHANGED], 0,
+  emit_signal (impl, signals[KBD_A11Y_MODS_STATE_CHANGED],
                  new_latched_mods, new_locked_mods);
 }
 
 void
 meta_seat_impl_notify_bell (MetaSeatImpl *impl)
 {
-  g_signal_emit (impl, signals[BELL], 0);
+  emit_signal (impl, signals[BELL], 0, 0);
 }
 
 MetaInputSettings *

src/backends/native/meta-seat-impl.h

@@ -54,7 +54,11 @@ struct _MetaSeatImpl
 {
   GObject parent_instance;
 
+  GMainContext *caller_context;
   GMainContext *input_context;
+  GMainLoop *input_loop;
+  GThread *input_thread;
+
   MetaSeatNative *seat;
   char *seat_id;
   MetaEventSource *event_source;
@@ -94,6 +98,7 @@ struct _MetaSeatImpl
   guint has_touchscreen          : 1;
   guint has_tablet_switch        : 1;
   guint touch_mode               : 1;
+  guint input_thread_initialized : 1;
 
   /* keyboard repeat */
   gboolean repeat;