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[gtk/ebassi/for-master: 6/6] a11y: Implement atspi.Cache


commit 9de2b4b0e1dbddb4fb891fb8e699c1c985ddeaf7
Author: Emmanuele Bassi <ebassi gnome org>
Date:   Mon Nov 16 15:23:37 2020 +0000

    a11y: Implement atspi.Cache
    
    The AT-SPI cache interface is used to quickly populate the accessible
    objects tree.
    
    The tricky bit is ensuring that we emit change notifications on the
    cache only when the cache is available, which means waiting until the
    root is asynchronously registered.

 gtk/a11y/gtkatspicache.c          | 214 ++++++++++++++++++++++++++++++++++----
 gtk/a11y/gtkatspicacheprivate.h   |  12 +--
 gtk/a11y/gtkatspicontext.c        |  91 +++++++++-------
 gtk/a11y/gtkatspicontextprivate.h |   6 ++
 gtk/a11y/gtkatspiroot.c           |  43 +++++++-
 gtk/a11y/gtkatspirootprivate.h    |  10 +-
 6 files changed, 309 insertions(+), 67 deletions(-)
---
diff --git a/gtk/a11y/gtkatspicache.c b/gtk/a11y/gtkatspicache.c
index 935af5acd1..31172d2cb6 100644
--- a/gtk/a11y/gtkatspicache.c
+++ b/gtk/a11y/gtkatspicache.c
@@ -22,10 +22,30 @@
 
 #include "gtkatspicacheprivate.h"
 
+#include "gtkatspicontextprivate.h"
+#include "gtkatspirootprivate.h"
+#include "gtkatspiutilsprivate.h"
 #include "gtkdebug.h"
 
 #include "a11y/atspi/atspi-cache.h"
 
+/* Cached item:
+ *
+ *  (so): object ref
+ *  (so): application ref
+ *  (so): parent ref
+ *    - parent.role == application ? desktop ref : null ref
+ *  i: index in parent, or -1 for transient widgets/menu items
+ *  i: child count, or -1 for defunct/menus
+ *  as: interfaces
+ *  s: name
+ *  u: role
+ *  s: description
+ *  au: state set
+ */
+#define ITEM_SIGNATURE          "(so)(so)(so)iiassusau"
+#define GET_ITEMS_SIGNATURE     "a(" ITEM_SIGNATURE ")"
+
 struct _GtkAtSpiCache
 {
   GObject parent_instance;
@@ -33,7 +53,11 @@ struct _GtkAtSpiCache
   char *cache_path;
   GDBusConnection *connection;
 
-  GHashTable *contexts;
+  /* HashTable<str, GtkAtSpiContext> */
+  GHashTable *contexts_by_path;
+
+  /* HashTable<GtkAtSpiContext, str> */
+  GHashTable *contexts_to_path;
 };
 
 enum
@@ -53,7 +77,8 @@ gtk_at_spi_cache_finalize (GObject *gobject)
 {
   GtkAtSpiCache *self = GTK_AT_SPI_CACHE (gobject);
 
-  g_clear_pointer (&self->contexts, g_hash_table_unref);
+  g_clear_pointer (&self->contexts_to_path, g_hash_table_unref);
+  g_clear_pointer (&self->contexts_by_path, g_hash_table_unref);
   g_clear_object (&self->connection);
   g_free (self->cache_path);
 
@@ -85,6 +110,98 @@ gtk_at_spi_cache_set_property (GObject      *gobject,
     }
 }
 
+static void
+collect_object (GtkAtSpiCache   *self,
+                GVariantBuilder *builder,
+                GtkAtSpiContext *context)
+{
+  g_variant_builder_add (builder, "@(so)", gtk_at_spi_context_to_ref (context));
+
+  GtkAtSpiRoot *root = gtk_at_spi_context_get_root (context);
+  g_variant_builder_add (builder, "@(so)", gtk_at_spi_root_to_ref (root));
+
+  g_variant_builder_add (builder, "@(so)", gtk_at_spi_context_get_parent_ref (context));
+
+  g_variant_builder_add (builder, "i", gtk_at_spi_context_get_index_in_parent (context));
+  g_variant_builder_add (builder, "i", gtk_at_spi_context_get_child_count (context));
+
+  g_variant_builder_add (builder, "@as", gtk_at_spi_context_get_interfaces (context));
+
+  char *name = gtk_at_context_get_name (GTK_AT_CONTEXT (context));
+  g_variant_builder_add (builder, "s", name ? name : "");
+  g_free (name);
+
+  guint atspi_role = gtk_atspi_role_for_context (GTK_AT_CONTEXT (context));
+  g_variant_builder_add (builder, "u", atspi_role);
+
+  char *description = gtk_at_context_get_description (GTK_AT_CONTEXT (context));
+  g_variant_builder_add (builder, "s", description ? description : "");
+  g_free (description);
+
+  g_variant_builder_add (builder, "@au", gtk_at_spi_context_get_states (context));
+}
+
+static void
+collect_cached_objects (GtkAtSpiCache   *self,
+                        GVariantBuilder *builder)
+{
+  GHashTable *collection = g_hash_table_new (NULL, NULL);
+  GHashTableIter iter;
+  gpointer key_p, value_p;
+
+  /* Serializing the contexts might re-enter, and end up modifying the hash
+   * table, so we take a snapshot here and return the items we have at the
+   * moment of the GetItems() call
+   */
+  g_hash_table_iter_init (&iter, self->contexts_by_path);
+  while (g_hash_table_iter_next (&iter, &key_p, &value_p))
+    g_hash_table_add (collection, value_p);
+
+  g_hash_table_iter_init (&iter, collection);
+  while (g_hash_table_iter_next (&iter, &key_p, &value_p))
+    {
+      g_variant_builder_open (builder, G_VARIANT_TYPE ("(" ITEM_SIGNATURE ")"));
+
+      GtkAtSpiContext *context = value_p;
+
+      collect_object (self, builder, context);
+
+      g_variant_builder_close (builder);
+    }
+
+  g_hash_table_unref (collection);
+}
+
+static void
+emit_add_accessible (GtkAtSpiCache   *self,
+                     GtkAtSpiContext *context)
+{
+  GVariantBuilder builder = G_VARIANT_BUILDER_INIT (G_VARIANT_TYPE ("(" ITEM_SIGNATURE ")"));
+
+  collect_object (self, &builder, context);
+
+  g_dbus_connection_emit_signal (self->connection,
+                                 NULL,
+                                 self->cache_path,
+                                 "org.a11y.atspi.Cache",
+                                 "AddAccessible",
+                                 g_variant_builder_end (&builder),
+                                 NULL);
+}
+
+static void
+emit_remove_accessible (GtkAtSpiCache *self,
+                        GVariant      *ref)
+{
+  g_dbus_connection_emit_signal (self->connection,
+                                 NULL,
+                                 self->cache_path,
+                                 "org.a11y.atspi.Cache",
+                                 "RemoveAccessible",
+                                 ref,
+                                 NULL);
+}
+
 static void
 handle_cache_method (GDBusConnection       *connection,
                      const gchar           *sender,
@@ -95,10 +212,23 @@ handle_cache_method (GDBusConnection       *connection,
                      GDBusMethodInvocation *invocation,
                      gpointer               user_data)
 {
+  GtkAtSpiCache *self = user_data;
+
   GTK_NOTE (A11Y,
             g_message ("[Cache] Method '%s' on interface '%s' for object '%s' from '%s'\n",
                        method_name, interface_name, object_path, sender));
 
+
+  if (g_strcmp0 (method_name, "GetItems") == 0)
+    {
+      GVariantBuilder builder = G_VARIANT_BUILDER_INIT (G_VARIANT_TYPE ("(" GET_ITEMS_SIGNATURE ")"));
+
+      g_variant_builder_open (&builder, G_VARIANT_TYPE (GET_ITEMS_SIGNATURE));
+      collect_cached_objects (self, &builder);
+      g_variant_builder_close (&builder);
+
+      g_dbus_method_invocation_return_value (invocation, g_variant_builder_end (&builder));
+    }
 }
 
 static GVariant *
@@ -175,9 +305,10 @@ gtk_at_spi_cache_class_init (GtkAtSpiCacheClass *klass)
 static void
 gtk_at_spi_cache_init (GtkAtSpiCache *self)
 {
-  self->contexts = g_hash_table_new_full (g_str_hash, g_str_equal,
-                                          g_free,
-                                          NULL);
+  self->contexts_by_path = g_hash_table_new_full (g_str_hash, g_str_equal,
+                                                  g_free,
+                                                  NULL);
+  self->contexts_to_path = g_hash_table_new (NULL, NULL);
 }
 
 GtkAtSpiCache *
@@ -193,27 +324,74 @@ gtk_at_spi_cache_new (GDBusConnection *connection,
                        NULL);
 }
 
+static void
+context_weak_unref (gpointer  data,
+                    GObject  *stale_context)
+{
+  GtkAtSpiCache *self = data;
+
+  const char *path = g_hash_table_lookup (self->contexts_to_path, stale_context);
+  if (path == NULL)
+    return;
+
+  /* By the time we get here, the context has already been dropped,
+   * so we need to generate the reference ourselves
+   */
+  emit_remove_accessible (self, g_variant_new ("(so)",
+                                               g_dbus_connection_get_unique_name (self->connection),
+                                               path));
+
+  GTK_NOTE (A11Y, g_message ("Removing stale context '%s' from cache", path));
+
+  g_hash_table_remove (self->contexts_by_path, path);
+  g_hash_table_remove (self->contexts_to_path, stale_context);
+}
+
 void
-gtk_at_spi_cache_add_context (GtkAtSpiCache *self,
-                              const char *path,
-                              GtkATContext *context)
+gtk_at_spi_cache_add_context (GtkAtSpiCache   *self,
+                              GtkAtSpiContext *context)
 {
   g_return_if_fail (GTK_IS_AT_SPI_CACHE (self));
-  g_return_if_fail (path != NULL);
-  g_return_if_fail (GTK_IS_AT_CONTEXT (context));
+  g_return_if_fail (GTK_IS_AT_SPI_CONTEXT (context));
+
+  const char *path = gtk_at_spi_context_get_context_path (context);
+  if (path == NULL)
+    return;
 
-  if (g_hash_table_contains (self->contexts, path))
+  if (g_hash_table_contains (self->contexts_by_path, path))
     return;
 
-  g_hash_table_insert (self->contexts, g_strdup (path), context);
+  g_object_weak_ref (G_OBJECT (context), context_weak_unref, self);
+
+  char *path_key = g_strdup (path);
+  g_hash_table_insert (self->contexts_by_path, path_key, context);
+  g_hash_table_insert (self->contexts_to_path, context, path_key);
+
+  emit_add_accessible (self, context);
+
+  GTK_NOTE (A11Y, g_message ("Adding context '%s' to cache", path_key));
 }
 
-GtkATContext *
-gtk_at_spi_cache_get_context (GtkAtSpiCache *self,
-                              const char *path)
+void
+gtk_at_spi_cache_remove_context (GtkAtSpiCache   *self,
+                                 GtkAtSpiContext *context)
 {
-  g_return_val_if_fail (GTK_IS_AT_SPI_CACHE (self), NULL);
-  g_return_val_if_fail (path != NULL, NULL);
+  g_return_if_fail (GTK_IS_AT_SPI_CACHE (self));
+  g_return_if_fail (GTK_IS_AT_SPI_CONTEXT (context));
+
+  const char *path = gtk_at_spi_context_get_context_path (context);
+  if (!g_hash_table_contains (self->contexts_by_path, path))
+    return;
+
+  emit_remove_accessible (self, gtk_at_spi_context_to_ref (context));
+
+  g_object_weak_unref (G_OBJECT (context), context_weak_unref, self);
+
+  /* The order is important: the value in contexts_by_path is the
+   * key in contexts_to_path
+   */
+  g_hash_table_remove (self->contexts_to_path, context);
+  g_hash_table_remove (self->contexts_by_path, path);
 
-  return g_hash_table_lookup (self->contexts, path);
+  GTK_NOTE (A11Y, g_message ("Removing context '%s' from cache", path));
 }
diff --git a/gtk/a11y/gtkatspicacheprivate.h b/gtk/a11y/gtkatspicacheprivate.h
index 12952a3c87..63f797ce5a 100644
--- a/gtk/a11y/gtkatspicacheprivate.h
+++ b/gtk/a11y/gtkatspicacheprivate.h
@@ -20,7 +20,8 @@
 
 #pragma once
 
-#include "gtkatcontextprivate.h"
+#include <gio/gio.h>
+#include "gtkatspiprivate.h"
 
 G_BEGIN_DECLS
 
@@ -34,11 +35,10 @@ gtk_at_spi_cache_new (GDBusConnection *connection,
 
 void
 gtk_at_spi_cache_add_context (GtkAtSpiCache *self,
-                              const char *path,
-                              GtkATContext *context);
+                              GtkAtSpiContext *context);
 
-GtkATContext *
-gtk_at_spi_cache_get_context (GtkAtSpiCache *self,
-                              const char *path);
+void
+gtk_at_spi_cache_remove_context (GtkAtSpiCache *self,
+                                 GtkAtSpiContext *context);
 
 G_END_DECLS
diff --git a/gtk/a11y/gtkatspicontext.c b/gtk/a11y/gtkatspicontext.c
index 28753f9f98..10eecbdfe4 100644
--- a/gtk/a11y/gtkatspicontext.c
+++ b/gtk/a11y/gtkatspicontext.c
@@ -632,17 +632,7 @@ handle_accessible_method (GDBusConnection       *connection,
     }
   else if (g_strcmp0 (method_name, "GetIndexInParent") == 0)
     {
-      GtkAccessible *accessible = gtk_at_context_get_accessible (GTK_AT_CONTEXT (self));
-      int idx;
-
-      if (GTK_IS_ROOT (accessible))
-        idx = get_index_in_toplevels (GTK_WIDGET (accessible));
-      else if (GTK_IS_STACK_PAGE (accessible))
-        idx = get_index_in_parent (gtk_stack_page_get_child (GTK_STACK_PAGE (accessible)));
-      else if (GTK_IS_STACK (gtk_widget_get_parent (GTK_WIDGET (accessible))))
-        idx = 1;
-      else
-        idx = get_index_in_parent (GTK_WIDGET (accessible));
+      int idx = gtk_at_spi_context_get_index_in_parent (self);
 
       if (idx == -1)
         g_dbus_method_invocation_return_error (invocation, G_DBUS_ERROR, G_DBUS_ERROR_FAILED, "Not found");
@@ -695,30 +685,7 @@ handle_accessible_get_property (GDBusConnection       *connection,
   else if (g_strcmp0 (property_name, "Parent") == 0)
     res = get_parent_context_ref (accessible);
   else if (g_strcmp0 (property_name, "ChildCount") == 0)
-    {
-      int n_children = 0;
-
-      if (GTK_IS_WIDGET (accessible))
-        {
-          GtkWidget *child;
-
-          for (child = gtk_widget_get_first_child (GTK_WIDGET (accessible));
-               child;
-               child = gtk_widget_get_next_sibling (child))
-            {
-              if (!gtk_accessible_should_present (GTK_ACCESSIBLE (child)))
-                continue;
-
-              n_children++;
-            }
-        }
-      else if (GTK_IS_STACK_PAGE (accessible))
-        {
-          n_children = 1;
-        }
-
-      res = g_variant_new_int32 (n_children);
-    }
+    res = g_variant_new_int32 (gtk_at_spi_context_get_child_count (self));
   else
     g_set_error (error, G_IO_ERROR, G_IO_ERROR_NOT_SUPPORTED,
                  "Unknown property '%s'", property_name);
@@ -1531,7 +1498,7 @@ gtk_at_spi_context_realize (GtkATContext *context)
                                        self);
   gtk_at_spi_context_register_object (self);
 
-  gtk_at_spi_root_queue_register (self->root);
+  gtk_at_spi_root_queue_register (self->root, self);
 }
 
 static void
@@ -1546,6 +1513,7 @@ gtk_at_spi_context_unrealize (GtkATContext *context)
 
   /* Notify ATs that the accessible object is going away */
   emit_defunct (self);
+  gtk_at_spi_root_unregister (self->root, self);
 
   gtk_atspi_disconnect_text_signals (accessible);
   gtk_atspi_disconnect_selection_signals (accessible);
@@ -1834,6 +1802,57 @@ gtk_at_spi_context_get_root (GtkAtSpiContext *self)
 
   return self->root;
 }
+
+int
+gtk_at_spi_context_get_index_in_parent (GtkAtSpiContext *self)
+{
+  g_return_val_if_fail (GTK_IS_AT_SPI_CONTEXT (self), -1);
+
+  GtkAccessible *accessible = gtk_at_context_get_accessible (GTK_AT_CONTEXT (self));
+  int idx;
+
+  if (GTK_IS_ROOT (accessible))
+    idx = get_index_in_toplevels (GTK_WIDGET (accessible));
+  else if (GTK_IS_STACK_PAGE (accessible))
+    idx = get_index_in_parent (gtk_stack_page_get_child (GTK_STACK_PAGE (accessible)));
+  else if (GTK_IS_STACK (gtk_widget_get_parent (GTK_WIDGET (accessible))))
+    idx = 1;
+  else
+    idx = get_index_in_parent (GTK_WIDGET (accessible));
+
+  return idx;
+}
+
+int
+gtk_at_spi_context_get_child_count (GtkAtSpiContext *self)
+{
+  g_return_val_if_fail (GTK_IS_AT_SPI_CONTEXT (self), -1);
+
+  GtkAccessible *accessible = gtk_at_context_get_accessible (GTK_AT_CONTEXT (self));
+  int n_children = -1;
+
+  if (GTK_IS_WIDGET (accessible))
+    {
+      GtkWidget *child;
+
+      n_children = 0;
+      for (child = gtk_widget_get_first_child (GTK_WIDGET (accessible));
+           child;
+           child = gtk_widget_get_next_sibling (child))
+        {
+          if (!gtk_accessible_should_present (GTK_ACCESSIBLE (child)))
+            continue;
+
+          n_children++;
+        }
+    }
+  else if (GTK_IS_STACK_PAGE (accessible))
+    {
+      n_children = 1;
+    }
+
+  return n_children;
+}
 /* }}} */
 
 /* vim:set foldmethod=marker expandtab: */
diff --git a/gtk/a11y/gtkatspicontextprivate.h b/gtk/a11y/gtkatspicontextprivate.h
index 0c95b8af07..2827bcd9ba 100644
--- a/gtk/a11y/gtkatspicontextprivate.h
+++ b/gtk/a11y/gtkatspicontextprivate.h
@@ -52,4 +52,10 @@ gtk_at_spi_context_get_interfaces (GtkAtSpiContext *self);
 GVariant *
 gtk_at_spi_context_get_states (GtkAtSpiContext *self);
 
+int
+gtk_at_spi_context_get_index_in_parent (GtkAtSpiContext *self);
+
+int
+gtk_at_spi_context_get_child_count (GtkAtSpiContext *self);
+
 G_END_DECLS
diff --git a/gtk/a11y/gtkatspiroot.c b/gtk/a11y/gtkatspiroot.c
index 583371bcec..9c23bd8e51 100644
--- a/gtk/a11y/gtkatspiroot.c
+++ b/gtk/a11y/gtkatspiroot.c
@@ -22,6 +22,7 @@
 
 #include "gtkatspirootprivate.h"
 
+#include "gtkatspicacheprivate.h"
 #include "gtkatspicontextprivate.h"
 #include "gtkaccessibleprivate.h"
 #include "gtkatspiprivate.h"
@@ -65,6 +66,7 @@ struct _GtkAtSpiRoot
   gint32 application_id;
   guint register_id;
 
+  GList *queued_contexts;
   GtkAtSpiCache *cache;
 
   GListModel *toplevels;
@@ -502,6 +504,15 @@ on_registration_reply (GObject      *gobject,
   /* Register the cache object */
   self->cache = gtk_at_spi_cache_new (self->connection, ATSPI_CACHE_PATH);
 
+  /* Drain the list of queued GtkAtSpiContexts, and add them to the cache */
+  if (self->queued_contexts != NULL)
+    {
+      for (GList *l = self->queued_contexts; l != NULL; l = l->next)
+        gtk_at_spi_cache_add_context (self->cache, l->data);
+
+      g_clear_pointer (&self->queued_contexts, g_list_free);
+    }
+
   self->toplevels = gtk_window_get_toplevels ();
 }
 
@@ -578,20 +589,42 @@ root_register (gpointer data)
  * Queues the registration of the root object on the AT-SPI bus.
  */
 void
-gtk_at_spi_root_queue_register (GtkAtSpiRoot *self)
+gtk_at_spi_root_queue_register (GtkAtSpiRoot    *self,
+                                GtkAtSpiContext *context)
 {
+  /* The cache is available if the root has finished registering itself; if we
+   * are still waiting for the registration to finish, add the context to a queue
+   */
+  if (self->cache != NULL)
+    {
+      gtk_at_spi_cache_add_context (self->cache, context);
+      return;
+    }
+  else
+    {
+      if (g_list_find (self->queued_contexts, context) == NULL)
+        self->queued_contexts = g_list_prepend (self->queued_contexts, context);
+    }
+
   /* Ignore multiple registration requests while one is already in flight */
   if (self->register_id != 0)
     return;
 
-  /* The cache is only available once the registration succeeds */
-  if (self->cache != NULL)
-    return;
-
   self->register_id = g_idle_add (root_register, self);
   g_source_set_name_by_id (self->register_id, "[gtk] ATSPI root registration");
 }
 
+void
+gtk_at_spi_root_unregister (GtkAtSpiRoot    *self,
+                            GtkAtSpiContext *context)
+{
+  if (self->queued_contexts != NULL)
+    self->queued_contexts = g_list_remove (self->queued_contexts, context);
+
+  if (self->cache != NULL)
+    gtk_at_spi_cache_remove_context (self->cache, context);
+}
+
 static void
 gtk_at_spi_root_constructed (GObject *gobject)
 {
diff --git a/gtk/a11y/gtkatspirootprivate.h b/gtk/a11y/gtkatspirootprivate.h
index 15a6b48548..d8d42c0e26 100644
--- a/gtk/a11y/gtkatspirootprivate.h
+++ b/gtk/a11y/gtkatspirootprivate.h
@@ -22,7 +22,8 @@
 
 #include <gio/gio.h>
 
-#include "gtkatspicacheprivate.h"
+#include "gtkatcontextprivate.h"
+#include "gtkatspiprivate.h"
 
 G_BEGIN_DECLS
 
@@ -34,7 +35,12 @@ GtkAtSpiRoot *
 gtk_at_spi_root_new (const char *bus_address);
 
 void
-gtk_at_spi_root_queue_register (GtkAtSpiRoot *self);
+gtk_at_spi_root_queue_register (GtkAtSpiRoot *self,
+                                GtkAtSpiContext *context);
+
+void
+gtk_at_spi_root_unregister (GtkAtSpiRoot *self,
+                            GtkAtSpiContext *context);
 
 GDBusConnection *
 gtk_at_spi_root_get_connection (GtkAtSpiRoot *self);
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