From 741dd674f6b488a123e96bfc109acaa9f5ad1235 Mon Sep 17 00:00:00 2001
From: Carlos Garnacho <carlosg@gnome.org>
Date: Fri, 26 Feb 2016 00:45:50 +0100
Subject: [PATCH] backends: rate-filter the emission of
 MetaBackend::last-device-changed signal

It indirectly triggers expensive operations in gnome-shell
(js/ui/keyboard.js), which turns out too expensive if we happen to operate
the shell simultaneously with 2 devices that will trigger the operations
there.

So just rate limit the signal emission, defer to an idle and just emit
the last device gotten. Worst that will happen is that we may possibly
emit the signal on the same device consecutively.

https://bugzilla.gnome.org/show_bug.cgi?id=753527
---
 src/backends/meta-backend.c | 60 +++++++++++++++++++++++++++----------
 1 file changed, 44 insertions(+), 16 deletions(-)

diff --git a/src/backends/meta-backend.c b/src/backends/meta-backend.c
index e4ef6e3cc..93c8ad326 100644
--- a/src/backends/meta-backend.c
+++ b/src/backends/meta-backend.c
@@ -64,6 +64,8 @@ struct _MetaBackendPrivate
   MetaInputSettings *input_settings;
 
   ClutterActor *stage;
+
+  guint device_update_idle_id;
 };
 typedef struct _MetaBackendPrivate MetaBackendPrivate;
 
@@ -78,6 +80,9 @@ meta_backend_finalize (GObject *object)
   g_clear_object (&priv->monitor_manager);
   g_clear_object (&priv->input_settings);
 
+  if (priv->device_update_idle_id)
+    g_source_remove (priv->device_update_idle_id);
+
   g_hash_table_destroy (backend->device_monitors);
 
   G_OBJECT_CLASS (meta_backend_parent_class)->finalize (object);
@@ -517,12 +522,44 @@ meta_backend_get_stage (MetaBackend *backend)
   return priv->stage;
 }
 
+static gboolean
+update_last_device (MetaBackend *backend)
+{
+  MetaCursorTracker *cursor_tracker = meta_cursor_tracker_get_for_screen (NULL);
+  MetaBackendPrivate *priv = meta_backend_get_instance_private (backend);
+  ClutterInputDeviceType device_type;
+  ClutterDeviceManager *manager;
+  ClutterInputDevice *device;
+
+  priv->device_update_idle_id = 0;
+  manager = clutter_device_manager_get_default ();
+  device = clutter_device_manager_get_device (manager,
+                                              backend->current_device_id);
+  device_type = clutter_input_device_get_device_type (device);
+
+  g_signal_emit_by_name (backend, "last-device-changed",
+                         backend->current_device_id);
+
+  switch (device_type)
+    {
+    case CLUTTER_KEYBOARD_DEVICE:
+      break;
+    case CLUTTER_TOUCHSCREEN_DEVICE:
+      meta_cursor_tracker_set_pointer_visible (cursor_tracker, FALSE);
+      break;
+    default:
+      meta_cursor_tracker_set_pointer_visible (cursor_tracker, TRUE);
+      break;
+    }
+
+  return G_SOURCE_REMOVE;
+}
+
 void
 meta_backend_update_last_device (MetaBackend *backend,
                                  int          device_id)
 {
-  ClutterInputDeviceType device_type;
-  MetaCursorTracker *cursor_tracker;
+  MetaBackendPrivate *priv = meta_backend_get_instance_private (backend);
   ClutterDeviceManager *manager;
   ClutterInputDevice *device;
 
@@ -536,23 +573,14 @@ meta_backend_update_last_device (MetaBackend *backend,
       clutter_input_device_get_device_mode (device) == CLUTTER_INPUT_MODE_MASTER)
     return;
 
-  device_type = clutter_input_device_get_device_type (device);
-
-  cursor_tracker = meta_cursor_tracker_get_for_screen (NULL);
   backend->current_device_id = device_id;
-  g_signal_emit_by_name (backend, "last-device-changed", device_id);
 
-  if (device_type == CLUTTER_KEYBOARD_DEVICE)
-    return;
-
-  switch (device_type)
+  if (priv->device_update_idle_id == 0)
     {
-    case CLUTTER_TOUCHSCREEN_DEVICE:
-      meta_cursor_tracker_set_pointer_visible (cursor_tracker, FALSE);
-      break;
-    default:
-      meta_cursor_tracker_set_pointer_visible (cursor_tracker, TRUE);
-      break;
+      priv->device_update_idle_id =
+        g_idle_add ((GSourceFunc) update_last_device, backend);
+      g_source_set_name_by_id (priv->device_update_idle_id,
+                               "[mutter] update_last_device");
     }
 }