[mutter/wip/carlosg/input-thread: 18/23] backends/native: Surround device state queries/updates with RW lock

[Carlos Garnacho <carlosg src gnome org>]

commit 6704e986a0022ac3300342b113461a2d6256c5ea
Author: Carlos Garnacho <carlosg gnome org>
Date:   Wed Aug 12 10:43:48 2020 +0200

    backends/native: Surround device state queries/updates with RW lock
    
    Wrap all keyboard state updates, and all pointer/stylus/touch cursor
    position with a write lock, and ::query_state() (The only entrypoint
    to this state from other threads) with a read lock.
    
    The principle is that query_state may be called from different threads
    (UI so far, but maybe KMS too in the future), while the input thread
    may (or may not) be updating it. This state is fetched "atomically"
    (eg. x/y will be consistently old or new, if the input thread were
    updating it at the same time).
    
    There's other places deep in backends/native that read this state,
    they all will run in the input thread, so they count as "other readers"
    to the other thread. Those changes are already mutually exclusive with
    updates, so they don't explicitly need the RW lock.
    
    https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1403

 src/backends/native/meta-input-device-native.c |  4 ++
 src/backends/native/meta-seat-impl.c           | 55 +++++++++++++++++++++++---
 src/backends/native/meta-seat-impl.h           |  1 +
 3 files changed, 54 insertions(+), 6 deletions(-)
---
diff --git a/src/backends/native/meta-input-device-native.c b/src/backends/native/meta-input-device-native.c
index ef09727125..8400004fb4 100644
--- a/src/backends/native/meta-input-device-native.c
+++ b/src/backends/native/meta-input-device-native.c
@@ -438,6 +438,8 @@ update_internal_xkb_state (MetaInputDeviceNative *device,
   xkb_mod_mask_t group_mods;
   struct xkb_state *xkb_state;
 
+  g_rw_lock_writer_lock (&seat_impl->state_lock);
+
   xkb_state = meta_seat_impl_get_xkb_state (seat_impl);
   depressed_mods = xkb_state_serialize_mods (xkb_state, XKB_STATE_MODS_DEPRESSED);
   latched_mods = xkb_state_serialize_mods (xkb_state, XKB_STATE_MODS_LATCHED);
@@ -460,6 +462,8 @@ update_internal_xkb_state (MetaInputDeviceNative *device,
                          locked_mods,
                          0, 0, group_mods);
   notify_stickykeys_mask (device);
+
+  g_rw_lock_writer_unlock (&seat_impl->state_lock);
 }
 
 static void
diff --git a/src/backends/native/meta-seat-impl.c b/src/backends/native/meta-seat-impl.c
index c1b27ef336..0afebf48d9 100644
--- a/src/backends/native/meta-seat-impl.c
+++ b/src/backends/native/meta-seat-impl.c
@@ -437,6 +437,8 @@ new_absolute_motion_event (MetaSeatImpl       *seat,
   clutter_event_set_device (event, seat->core_pointer);
   clutter_event_set_source_device (event, input_device);
 
+  g_rw_lock_writer_lock (&seat->state_lock);
+
   if (clutter_input_device_get_device_type (input_device) == CLUTTER_TABLET_DEVICE)
     {
       MetaInputDeviceNative *device_evdev =
@@ -460,6 +462,8 @@ new_absolute_motion_event (MetaSeatImpl       *seat,
       seat->pointer_y = y;
     }
 
+  g_rw_lock_writer_unlock (&seat->state_lock);
+
   return event;
 }
 
@@ -2010,10 +2014,14 @@ process_device_event (MetaSeatImpl          *seat,
         y = libinput_event_touch_get_y_transformed (touch_event,
                                                     stage_height);
 
+        g_rw_lock_writer_lock (&seat->state_lock);
+
         touch_state = meta_seat_impl_acquire_touch_state (seat, seat_slot);
         touch_state->coords.x = x;
         touch_state->coords.y = y;
 
+        g_rw_lock_writer_unlock (&seat->state_lock);
+
         meta_seat_impl_notify_touch_event (seat, device,
                                            CLUTTER_TOUCH_BEGIN,
                                            time_us,
@@ -2047,7 +2055,10 @@ process_device_event (MetaSeatImpl          *seat,
                                            touch_state->seat_slot,
                                            touch_state->coords.x,
                                            touch_state->coords.y);
+
+        g_rw_lock_writer_lock (&seat->state_lock);
         meta_seat_impl_release_touch_state (seat, seat_slot);
+        g_rw_lock_writer_unlock (&seat->state_lock);
         break;
       }
 
@@ -2076,13 +2087,18 @@ process_device_event (MetaSeatImpl          *seat,
         y = libinput_event_touch_get_y_transformed (touch_event,
                                                     stage_height);
 
+        g_rw_lock_writer_lock (&seat->state_lock);
         touch_state = meta_seat_impl_lookup_touch_state (seat, seat_slot);
+        if (touch_state)
+          {
+            touch_state->coords.x = x;
+            touch_state->coords.y = y;
+          }
+        g_rw_lock_writer_unlock (&seat->state_lock);
+
         if (!touch_state)
           break;
 
-        touch_state->coords.x = x;
-        touch_state->coords.y = y;
-
         meta_seat_impl_notify_touch_event (seat, device,
                                            CLUTTER_TOUCH_UPDATE,
                                            time_us,
@@ -2443,6 +2459,8 @@ meta_seat_impl_constructed (GObject *object)
   struct udev *udev;
   struct xkb_keymap *xkb_keymap;
 
+  g_rw_lock_writer_lock (&seat->state_lock);
+
   device = meta_input_device_native_new_virtual (
       seat, CLUTTER_POINTER_DEVICE,
       CLUTTER_INPUT_MODE_MASTER);
@@ -2504,6 +2522,8 @@ meta_seat_impl_constructed (GObject *object)
         xkb_keymap_led_get_index (xkb_keymap, XKB_LED_NAME_SCROLL);
     }
 
+  g_rw_lock_writer_unlock (&seat->state_lock);
+
   seat->has_touchscreen = has_touchscreen (seat);
   update_touch_mode (seat);
 
@@ -2599,6 +2619,8 @@ meta_seat_impl_finalize (GObject *object)
 
   g_free (seat->seat_id);
 
+  g_rw_lock_clear (&seat->state_lock);
+
   G_OBJECT_CLASS (meta_seat_impl_parent_class)->finalize (object);
 }
 
@@ -2661,6 +2683,9 @@ meta_seat_impl_query_state (MetaSeatImpl         *seat,
 {
   MetaInputDeviceNative *device_native = META_INPUT_DEVICE_NATIVE (device);
   MetaSeatImpl *seat_native = META_SEAT_IMPL (seat);
+  gboolean retval = FALSE;
+
+  g_rw_lock_reader_lock (&seat->state_lock);
 
   if (sequence)
     {
@@ -2670,7 +2695,7 @@ meta_seat_impl_query_state (MetaSeatImpl         *seat,
       slot = meta_event_native_sequence_get_slot (sequence);
       touch_state = meta_seat_impl_lookup_touch_state (seat_native, slot);
       if (!touch_state)
-        return FALSE;
+        goto out;
 
       if (coords)
         {
@@ -2681,7 +2706,7 @@ meta_seat_impl_query_state (MetaSeatImpl         *seat,
       if (modifiers)
         *modifiers = meta_xkb_translate_modifiers (seat_native->xkb, 0);
 
-      return TRUE;
+      retval = TRUE;
     }
   else
     {
@@ -2697,8 +2722,12 @@ meta_seat_impl_query_state (MetaSeatImpl         *seat,
                                                      seat_native->button_state);
         }
 
-      return TRUE;
+      retval = TRUE;
     }
+
+ out:
+  g_rw_lock_reader_unlock (&seat->state_lock);
+  return retval;
 }
 
 static void
@@ -2769,6 +2798,8 @@ meta_seat_impl_class_init (MetaSeatImplClass *klass)
 static void
 meta_seat_impl_init (MetaSeatImpl *seat)
 {
+  g_rw_lock_init (&seat->state_lock);
+
   seat->device_id_next = INITIAL_DEVICE_ID;
 
   seat->repeat = TRUE;
@@ -2810,6 +2841,8 @@ meta_seat_impl_update_xkb_state (MetaSeatImpl *seat)
   xkb_mod_mask_t locked_mods;
   struct xkb_keymap *xkb_keymap;
 
+  g_rw_lock_writer_lock (&seat->state_lock);
+
   xkb_keymap = meta_keymap_native_get_keyboard_map (seat->keymap);
 
   latched_mods = xkb_state_serialize_mods (seat->xkb,
@@ -2830,6 +2863,8 @@ meta_seat_impl_update_xkb_state (MetaSeatImpl *seat)
   seat->scroll_lock_led = xkb_keymap_led_get_index (xkb_keymap, XKB_LED_NAME_SCROLL);
 
   meta_seat_impl_sync_leds (seat);
+
+  g_rw_lock_writer_unlock (&seat->state_lock);
 }
 
 gint
@@ -2990,6 +3025,8 @@ meta_seat_impl_set_keyboard_layout_index (MetaSeatImpl       *seat,
 
   g_return_if_fail (META_IS_SEAT_IMPL (seat));
 
+  g_rw_lock_writer_lock (&seat->state_lock);
+
   state = seat->xkb;
 
   depressed_mods = xkb_state_serialize_mods (state, XKB_STATE_MODS_DEPRESSED);
@@ -2999,6 +3036,8 @@ meta_seat_impl_set_keyboard_layout_index (MetaSeatImpl       *seat,
   xkb_state_update_mask (state, depressed_mods, latched_mods, locked_mods, 0, 0, idx);
 
   seat->layout_idx = idx;
+
+  g_rw_lock_writer_unlock (&seat->state_lock);
 }
 
 /**
@@ -3031,6 +3070,8 @@ meta_seat_impl_set_keyboard_numlock (MetaSeatImpl *seat,
 
   g_return_if_fail (META_IS_SEAT_IMPL (seat));
 
+  g_rw_lock_writer_lock (&seat->state_lock);
+
   keymap = seat->keymap;
   xkb_keymap = meta_keymap_native_get_keyboard_map (keymap);
 
@@ -3054,6 +3095,8 @@ meta_seat_impl_set_keyboard_numlock (MetaSeatImpl *seat,
                          group_mods);
 
   meta_seat_impl_sync_leds (seat);
+
+  g_rw_lock_writer_unlock (&seat->state_lock);
 }
 
 /**
diff --git a/src/backends/native/meta-seat-impl.h b/src/backends/native/meta-seat-impl.h
index 1b20e80c24..8cc5cae15c 100644
--- a/src/backends/native/meta-seat-impl.h
+++ b/src/backends/native/meta-seat-impl.h
@@ -59,6 +59,7 @@ struct _MetaSeatImpl
   MetaEventSource *event_source;
   struct libinput *libinput;
   struct libinput_seat *libinput_seat;
+  GRWLock state_lock;
 
   GSList *devices;