[gnome-builder] highlighter: be safer with usage of borrowed reference

[Christian Hergert <chergert src gnome org>]

commit cb72e5427c6adbd643fe6c9612fcf71e3df13fb9
Author: Christian Hergert <chergert redhat com>
Date:   Fri Jan 12 15:13:49 2018 -0800

    highlighter: be safer with usage of borrowed reference
    
    Instead of stashing a pointer, unchecked, use GWeakRef to protect our
    borrowed instance.

 src/libide/highlighting/ide-highlight-engine.c | 195 ++++++++++++++++---------
 1 file changed, 125 insertions(+), 70 deletions(-)
---
diff --git a/src/libide/highlighting/ide-highlight-engine.c b/src/libide/highlighting/ide-highlight-engine.c
index 56ed90a12..b5d6c83d2 100644
--- a/src/libide/highlighting/ide-highlight-engine.c
+++ b/src/libide/highlighting/ide-highlight-engine.c
@@ -37,8 +37,9 @@ struct _IdeHighlightEngine
 {
   IdeObject            parent_instance;
 
+  GWeakRef             buffer_wref;
+
   DzlSignalGroup      *signal_group;
-  IdeBuffer           *buffer;
   IdeHighlighter      *highlighter;
   GSettings           *settings;
 
@@ -220,33 +221,43 @@ static GtkTextTag *
 create_tag_from_style (IdeHighlightEngine *self,
                        const gchar        *style_name)
 {
+  g_autoptr(IdeBuffer) buffer = NULL;
   GtkSourceStyleScheme *style_scheme;
-  GtkTextTag *tag;
+  GtkTextTag *tag = NULL;
 
   g_assert (IDE_IS_HIGHLIGHT_ENGINE (self));
-  g_assert (IDE_IS_BUFFER (self->buffer));
   g_assert (style_name != NULL);
 
-  tag = gtk_text_buffer_create_tag (GTK_TEXT_BUFFER (self->buffer), style_name, NULL);
-  gtk_text_tag_set_priority (tag, 0);
-  style_scheme = gtk_source_buffer_get_style_scheme (GTK_SOURCE_BUFFER (self->buffer));
-  sync_tag_style (style_scheme, tag);
+  buffer = g_weak_ref_get (&self->buffer_wref);
+
+  if (buffer != NULL)
+    {
+      tag = gtk_text_buffer_create_tag (GTK_TEXT_BUFFER (buffer), style_name, NULL);
+      gtk_text_tag_set_priority (tag, 0);
+      style_scheme = gtk_source_buffer_get_style_scheme (GTK_SOURCE_BUFFER (buffer));
+      sync_tag_style (style_scheme, tag);
+    }
 
   return tag;
 }
 
-GtkTextTag *
+static GtkTextTag *
 get_tag_from_style (IdeHighlightEngine *self,
                     const gchar        *style_name,
                     gboolean            private_tag)
 {
+  g_autoptr(IdeBuffer) buffer = NULL;
+  g_autofree gchar *tmp_style_name = NULL;
   GtkTextTagTable *tag_table;
   GtkTextTag *tag;
-  g_autofree gchar *tmp_style_name = NULL;
 
   g_return_val_if_fail (IDE_IS_HIGHLIGHT_ENGINE (self), NULL);
   g_return_val_if_fail (style_name != NULL, NULL);
 
+  buffer = g_weak_ref_get (&self->buffer_wref);
+  if (buffer == NULL)
+    return NULL;
+
   /*
    * If is private tag prepend the PRIVATE_TAG_PREFIX (gb-private-tag)
    * to the string.This is used because tag name is the key used
@@ -258,7 +269,7 @@ get_tag_from_style (IdeHighlightEngine *self,
   else
     tmp_style_name = g_strdup (style_name);
 
-  tag_table = gtk_text_buffer_get_tag_table (GTK_TEXT_BUFFER (self->buffer));
+  tag_table = gtk_text_buffer_get_tag_table (GTK_TEXT_BUFFER (buffer));
   tag = gtk_text_tag_table_lookup (tag_table, tmp_style_name);
 
   if (tag == NULL)
@@ -307,14 +318,15 @@ ide_highlight_engine_tick (IdeHighlightEngine *self)
   IDE_PROBE;
 
   g_assert (IDE_IS_HIGHLIGHT_ENGINE (self));
-  g_assert (self->buffer != NULL);
   g_assert (self->highlighter != NULL);
   g_assert (self->invalid_begin != NULL);
   g_assert (self->invalid_end != NULL);
 
-  self->quanta_expiration = g_get_monotonic_time () + HIGHLIGHT_QUANTA_USEC;
+  buffer = g_weak_ref_get (&self->buffer_wref);
+  if (buffer == NULL)
+    return G_SOURCE_REMOVE;
 
-  buffer = GTK_TEXT_BUFFER (self->buffer);
+  self->quanta_expiration = g_get_monotonic_time () + HIGHLIGHT_QUANTA_USEC;
 
   gtk_text_buffer_get_iter_at_mark (buffer, &invalid_begin, self->invalid_begin);
   gtk_text_buffer_get_iter_at_mark (buffer, &invalid_end, self->invalid_end);
@@ -346,18 +358,18 @@ ide_highlight_engine_tick (IdeHighlightEngine *self)
 
   /* Stop processing until further instruction if no movement was made */
   if (gtk_text_iter_equal (&iter, &invalid_begin))
-    return FALSE;
+    return G_SOURCE_REMOVE;
 
   gtk_text_buffer_move_mark (buffer, self->invalid_begin, &iter);
 
-  return TRUE;
+  return G_SOURCE_CONTINUE;
 
 up_to_date:
   gtk_text_buffer_get_start_iter (buffer, &iter);
   gtk_text_buffer_move_mark (buffer, self->invalid_begin, &iter);
   gtk_text_buffer_move_mark (buffer, self->invalid_end, &iter);
 
-  return FALSE;
+  return G_SOURCE_REMOVE;
 }
 
 static gboolean
@@ -381,9 +393,12 @@ ide_highlight_engine_work_timeout_handler (gpointer data)
 static void
 ide_highlight_engine_queue_work (IdeHighlightEngine *self)
 {
+  g_autoptr(GtkTextBuffer) buffer = NULL;
+
   g_assert (IDE_IS_HIGHLIGHT_ENGINE (self));
 
-  if ((self->highlighter == NULL) || (self->buffer == NULL) || (self->work_timeout != 0))
+  buffer = g_weak_ref_get (&self->buffer_wref);
+  if (self->highlighter == NULL || buffer == NULL || self->work_timeout != 0)
     return;
 
   /*
@@ -406,6 +421,7 @@ invalidate_and_highlight (IdeHighlightEngine *self,
                           GtkTextIter        *begin,
                           GtkTextIter        *end)
 {
+  GtkTextBuffer *text_buffer;
 
   g_assert (IDE_IS_HIGHLIGHT_ENGINE (self));
   g_assert (begin != NULL);
@@ -414,11 +430,12 @@ invalidate_and_highlight (IdeHighlightEngine *self,
   if (!self->enabled)
     return FALSE;
 
+  text_buffer = gtk_text_iter_get_buffer (begin);
+
   if (get_invalidation_area (begin, end))
     {
       GtkTextIter begin_tmp;
       GtkTextIter end_tmp;
-      GtkTextBuffer *text_buffer = GTK_TEXT_BUFFER (self->buffer);
 
       gtk_text_buffer_get_iter_at_mark (text_buffer, &begin_tmp, self->invalid_begin);
       gtk_text_buffer_get_iter_at_mark (text_buffer, &end_tmp, self->invalid_end);
@@ -447,7 +464,7 @@ invalidate_and_highlight (IdeHighlightEngine *self,
 static void
 ide_highlight_engine_reload (IdeHighlightEngine *self)
 {
-  GtkTextBuffer *buffer;
+  g_autoptr(GtkTextBuffer) buffer = NULL;
   GtkTextIter begin;
   GtkTextIter end;
   GSList *iter;
@@ -456,17 +473,12 @@ ide_highlight_engine_reload (IdeHighlightEngine *self)
 
   g_assert (IDE_IS_HIGHLIGHT_ENGINE (self));
 
-  if (self->work_timeout != 0)
-    {
-      g_source_remove (self->work_timeout);
-      self->work_timeout = 0;
-    }
+  dzl_clear_source (&self->work_timeout);
 
-  if (self->buffer == NULL)
+  buffer = g_weak_ref_get (&self->buffer_wref);
+  if (buffer == NULL)
     IDE_EXIT;
 
-  buffer = GTK_TEXT_BUFFER (self->buffer);
-
   gtk_text_buffer_get_bounds (buffer, &begin, &end);
 
   /*
@@ -621,20 +633,23 @@ ide_highlight_engine__notify_style_scheme_cb (IdeHighlightEngine *self,
 void
 ide_highlight_engine_clear (IdeHighlightEngine *self)
 {
+  g_autoptr(GtkTextBuffer) buffer = NULL;
   GtkTextIter begin;
   GtkTextIter end;
 
   g_assert (IDE_IS_HIGHLIGHT_ENGINE (self));
 
-  if (self->buffer != NULL)
-    {
-      GtkTextBuffer *buffer = GTK_TEXT_BUFFER (self->buffer);
-      GSList *iter;
+  buffer = g_weak_ref_get (&self->buffer_wref);
 
-      gtk_text_buffer_get_bounds (GTK_TEXT_BUFFER (self->buffer), &begin, &end);
+  if (buffer != NULL)
+    {
+      gtk_text_buffer_get_bounds (buffer, &begin, &end);
 
-      for (iter = self->public_tags; iter; iter = iter->next)
-        gtk_text_buffer_remove_tag (buffer, iter->data, &begin, &end);
+      for (const GSList *iter = self->public_tags; iter; iter = iter->next)
+        {
+          GtkTextTag *tag = iter->data;
+          gtk_text_buffer_remove_tag (buffer, tag, &begin, &end);
+        }
     }
 }
 
@@ -652,14 +667,23 @@ ide_highlight_engine__bind_buffer_cb (IdeHighlightEngine *self,
   g_assert (IDE_IS_HIGHLIGHT_ENGINE (self));
   g_assert (IDE_IS_BUFFER (buffer));
   g_assert (DZL_IS_SIGNAL_GROUP (group));
+  g_assert (self->invalid_begin == NULL);
+  g_assert (self->invalid_end == NULL);
 
-  self->buffer = buffer;
+  g_weak_ref_set (&self->buffer_wref, buffer);
 
   gtk_text_buffer_get_bounds (text_buffer, &begin, &end);
 
   self->invalid_begin = gtk_text_buffer_create_mark (text_buffer, NULL, &begin, TRUE);
   self->invalid_end = gtk_text_buffer_create_mark (text_buffer, NULL, &end, FALSE);
 
+  /* We can hold a full reference to the text marks, without
+   * taking a reference to the buffer. We want to avoid a reference
+   * to the buffer for cyclic reasons.
+   */
+  g_object_ref (self->invalid_begin);
+  g_object_ref (self->invalid_end);
+
   ide_highlight_engine__notify_style_scheme_cb (self, NULL, buffer);
   ide_highlight_engine__notify_language_cb (self, NULL, buffer);
 
@@ -672,47 +696,53 @@ static void
 ide_highlight_engine__unbind_buffer_cb (IdeHighlightEngine  *self,
                                         DzlSignalGroup      *group)
 {
-  GtkTextBuffer *text_buffer;
-  GtkTextTagTable *tag_table;
-  GtkTextIter begin;
-  GtkTextIter end;
-  GSList *iter;
+  g_autoptr(GtkTextBuffer) text_buffer = NULL;
 
   IDE_ENTRY;
 
   g_assert (IDE_IS_HIGHLIGHT_ENGINE (self));
   g_assert (DZL_IS_SIGNAL_GROUP (group));
-  g_assert (GTK_IS_TEXT_BUFFER (self->buffer));
 
-  text_buffer = GTK_TEXT_BUFFER (self->buffer);
+  text_buffer = g_weak_ref_get (&self->buffer_wref);
 
   dzl_clear_source (&self->work_timeout);
 
-  tag_table = gtk_text_buffer_get_tag_table (text_buffer);
+  if (text_buffer != NULL)
+    {
+      g_autoptr(GSList) private_tags = NULL;
+      g_autoptr(GSList) public_tags = NULL;
+      GtkTextTagTable *tag_table;
+      GtkTextIter begin;
+      GtkTextIter end;
 
-  gtk_text_buffer_delete_mark (text_buffer, self->invalid_begin);
-  gtk_text_buffer_delete_mark (text_buffer, self->invalid_end);
+      tag_table = gtk_text_buffer_get_tag_table (text_buffer);
 
-  self->invalid_begin = NULL;
-  self->invalid_end = NULL;
+      gtk_text_buffer_delete_mark (text_buffer, self->invalid_begin);
+      gtk_text_buffer_delete_mark (text_buffer, self->invalid_end);
 
-  gtk_text_buffer_get_bounds (text_buffer, &begin, &end);
+      gtk_text_buffer_get_bounds (text_buffer, &begin, &end);
 
-  for (iter = self->private_tags; iter; iter = iter->next)
-    {
-      gtk_text_buffer_remove_tag (text_buffer, iter->data, &begin, &end);
-      gtk_text_tag_table_remove (tag_table, iter->data);
-    }
-  g_clear_pointer (&self->private_tags, g_slist_free);
+      private_tags = g_steal_pointer (&self->private_tags);
+      public_tags = g_steal_pointer (&self->public_tags);
 
-  for (iter = self->public_tags; iter; iter = iter->next)
-    {
-      gtk_text_buffer_remove_tag (text_buffer, iter->data, &begin, &end);
-      gtk_text_tag_table_remove (tag_table, iter->data);
+      for (const GSList *iter = private_tags; iter; iter = iter->next)
+        {
+          gtk_text_buffer_remove_tag (text_buffer, iter->data, &begin, &end);
+          gtk_text_tag_table_remove (tag_table, iter->data);
+        }
+
+      for (const GSList *iter = public_tags; iter; iter = iter->next)
+        {
+          gtk_text_buffer_remove_tag (text_buffer, iter->data, &begin, &end);
+          gtk_text_tag_table_remove (tag_table, iter->data);
+        }
     }
+
   g_clear_pointer (&self->public_tags, g_slist_free);
+  g_clear_pointer (&self->private_tags, g_slist_free);
 
-  self->buffer = NULL;
+  g_clear_object (&self->invalid_begin);
+  g_clear_object (&self->invalid_end);
 
   IDE_EXIT;
 }
@@ -797,16 +827,25 @@ ide_highlight_engine_dispose (GObject *object)
 {
   IdeHighlightEngine *self = (IdeHighlightEngine *)object;
 
+  g_weak_ref_set (&self->buffer_wref, NULL);
   g_clear_object (&self->signal_group);
   g_clear_object (&self->extension);
   g_clear_object (&self->highlighter);
   g_clear_object (&self->settings);
 
-  g_assert (self->buffer == NULL);
-
   G_OBJECT_CLASS (ide_highlight_engine_parent_class)->dispose (object);
 }
 
+static void
+ide_highlight_engine_finalize (GObject *object)
+{
+  IdeHighlightEngine *self = (IdeHighlightEngine *)object;
+
+  g_weak_ref_clear (&self->buffer_wref);
+
+  G_OBJECT_CLASS (ide_highlight_engine_parent_class)->finalize (object);
+}
+
 static void
 ide_highlight_engine_get_property (GObject    *object,
                                    guint       prop_id,
@@ -856,6 +895,7 @@ ide_highlight_engine_class_init (IdeHighlightEngineClass *klass)
 
   object_class->constructed = ide_highlight_engine_constructed;
   object_class->dispose = ide_highlight_engine_dispose;
+  object_class->finalize = ide_highlight_engine_finalize;
   object_class->get_property = ide_highlight_engine_get_property;
   object_class->set_property = ide_highlight_engine_set_property;
 
@@ -879,6 +919,8 @@ ide_highlight_engine_class_init (IdeHighlightEngineClass *klass)
 static void
 ide_highlight_engine_init (IdeHighlightEngine *self)
 {
+  g_weak_ref_init (&self->buffer_wref, NULL);
+
   self->settings = g_settings_new ("org.gnome.builder.code-insight");
   self->enabled = g_settings_get_boolean (self->settings, "semantic-highlighting");
   self->signal_group = dzl_signal_group_new (IDE_TYPE_BUFFER);
@@ -970,27 +1012,38 @@ ide_highlight_engine_get_highlighter (IdeHighlightEngine *self)
 IdeBuffer *
 ide_highlight_engine_get_buffer (IdeHighlightEngine *self)
 {
+  g_autoptr(IdeBuffer) buffer = NULL;
+
   g_return_val_if_fail (IDE_IS_HIGHLIGHT_ENGINE (self), NULL);
 
-  return self->buffer;
+  /* We don't need the "thread-safety" provided by GWeakRef here,
+   * (where it gives us a new object reference). It is safe to
+   * return a borrowed reference instead.
+   */
+  buffer = g_weak_ref_get (&self->buffer_wref);
+  return buffer;
 }
 
 void
 ide_highlight_engine_rebuild (IdeHighlightEngine *self)
 {
+  g_autoptr(GtkTextBuffer) buffer = NULL;
+
   IDE_ENTRY;
 
   g_return_if_fail (IDE_IS_HIGHLIGHT_ENGINE (self));
 
-  if (self->buffer != NULL)
+  buffer = g_weak_ref_get (&self->buffer_wref);
+
+  if (buffer != NULL)
     {
-      GtkTextBuffer *buffer = GTK_TEXT_BUFFER (self->buffer);
       GtkTextIter begin;
       GtkTextIter end;
 
       gtk_text_buffer_get_bounds (buffer, &begin, &end);
       gtk_text_buffer_move_mark (buffer, self->invalid_begin, &begin);
       gtk_text_buffer_move_mark (buffer, self->invalid_end, &end);
+
       ide_highlight_engine_queue_work (self);
     }
 
@@ -1027,10 +1080,8 @@ ide_highlight_engine_invalidate (IdeHighlightEngine *self,
   g_return_if_fail (IDE_IS_HIGHLIGHT_ENGINE (self));
   g_return_if_fail (begin != NULL);
   g_return_if_fail (end != NULL);
-  g_return_if_fail (gtk_text_iter_get_buffer (begin) == GTK_TEXT_BUFFER (self->buffer));
-  g_return_if_fail (gtk_text_iter_get_buffer (end) == GTK_TEXT_BUFFER (self->buffer));
 
-  buffer = GTK_TEXT_BUFFER (self->buffer);
+  buffer = gtk_text_iter_get_buffer (begin);
 
   gtk_text_buffer_get_iter_at_mark (buffer, &mark_begin, self->invalid_begin);
   gtk_text_buffer_get_iter_at_mark (buffer, &mark_end, self->invalid_end);
@@ -1080,16 +1131,20 @@ ide_highlight_engine_pause (IdeHighlightEngine *self)
 void
 ide_highlight_engine_unpause (IdeHighlightEngine *self)
 {
+  g_autoptr(IdeBuffer) buffer = NULL;
+
   g_return_if_fail (IDE_IS_HIGHLIGHT_ENGINE (self));
   g_return_if_fail (self->signal_group != NULL);
 
   dzl_signal_group_unblock (self->signal_group);
 
-  if (self->buffer != NULL)
+  buffer = g_weak_ref_get (&self->buffer_wref);
+
+  if (buffer != NULL)
     {
       /* Notify of some blocked signals */
-      ide_highlight_engine__notify_style_scheme_cb (self, NULL, self->buffer);
-      ide_highlight_engine__notify_language_cb (self, NULL, self->buffer);
+      ide_highlight_engine__notify_style_scheme_cb (self, NULL, buffer);
+      ide_highlight_engine__notify_language_cb (self, NULL, buffer);
 
       ide_highlight_engine_reload (self);
     }