[gimp] libgimp: add some debug code to warn about broken proxy handling

[Michael Natterer <mitch src gnome org>]

commit eb311be1200e1ea3997cef85023e6ba0bdd19293
Author: Michael Natterer <mitch gimp org>
Date:   Tue Aug 27 17:24:56 2019 +0200

    libgimp: add some debug code to warn about broken proxy handling
    
    Add an additional ref count to all proxies handed out by
    GimpPlugIn, and when destroying the proxies, warn about any
    proxy that has been unrefed, or additionally refed.
    
    This catches and warns about only one broken unref, any more will
    simply crash like before.

 libgimp/gimpplugin.c | 139 ++++++++++++++++++++++++++++-----------------------
 1 file changed, 77 insertions(+), 62 deletions(-)
---
diff --git a/libgimp/gimpplugin.c b/libgimp/gimpplugin.c
index 94f04d00a1..6c7be62a36 100644
--- a/libgimp/gimpplugin.c
+++ b/libgimp/gimpplugin.c
@@ -142,7 +142,9 @@ static void       gimp_plug_in_push_procedure    (GimpPlugIn      *plug_in,
                                                   GimpProcedure   *procedure);
 static void       gimp_plug_in_pop_procedure     (GimpPlugIn      *plug_in,
                                                   GimpProcedure   *procedure);
-static void       gimp_plug_in_destroy_proxies   (GimpPlugIn      *plug_in);
+static void       gimp_plug_in_destroy_hashes    (GimpPlugIn      *plug_in);
+static void       gimp_plug_in_destroy_proxies   (GHashTable      *hash_table,
+                                                  gboolean         finalize);
 
 
 G_DEFINE_TYPE_WITH_PRIVATE (GimpPlugIn, gimp_plug_in, G_TYPE_OBJECT)
@@ -238,7 +240,11 @@ gimp_plug_in_finalize (GObject *object)
 
   g_clear_pointer (&plug_in->priv->menu_branches, g_list_free);
 
-  gimp_plug_in_destroy_proxies (plug_in);
+  gimp_plug_in_destroy_proxies (plug_in->priv->displays, TRUE);
+  gimp_plug_in_destroy_proxies (plug_in->priv->images,   TRUE);
+  gimp_plug_in_destroy_proxies (plug_in->priv->items,    TRUE);
+
+  gimp_plug_in_destroy_hashes (plug_in);
 
   G_OBJECT_CLASS (parent_class)->finalize (object);
 }
@@ -1213,63 +1219,12 @@ gimp_plug_in_pop_procedure (GimpPlugIn    *plug_in,
 
   _gimp_procedure_destroy_proxies (procedure);
 
-  if (plug_in->priv->procedure_stack)
-    {
-      GHashTableIter iter;
-      gpointer       key, value;
+  gimp_plug_in_destroy_proxies (plug_in->priv->displays, FALSE);
+  gimp_plug_in_destroy_proxies (plug_in->priv->images,   FALSE);
+  gimp_plug_in_destroy_proxies (plug_in->priv->items,    FALSE);
 
-      if (plug_in->priv->displays)
-        {
-          g_hash_table_iter_init (&iter, plug_in->priv->displays);
-          while (g_hash_table_iter_next (&iter, &key, &value))
-            {
-              GObject *object = value;
-
-              if (object->ref_count == 1)
-                g_hash_table_iter_remove (&iter);
-            }
-        }
-
-      if (plug_in->priv->images)
-        {
-          g_hash_table_iter_init (&iter, plug_in->priv->images);
-          while (g_hash_table_iter_next (&iter, &key, &value))
-            {
-              GObject *object = value;
-
-              if (object->ref_count == 1)
-                g_hash_table_iter_remove (&iter);
-            }
-        }
-
-      if (plug_in->priv->items)
-        {
-          g_hash_table_iter_init (&iter, plug_in->priv->items);
-          while (g_hash_table_iter_next (&iter, &key, &value))
-            {
-              GObject *object = value;
-
-              if (object->ref_count == 1)
-                g_hash_table_iter_remove (&iter);
-            }
-        }
-    }
-  else
-    {
-#if 0
-      g_printerr ("remaining displays: %d\n"
-                  "remaining images:   %d\n"
-                  "remaining items;    %d\n",
-                  plug_in->priv->displays ?
-                  g_hash_table_size (plug_in->priv->displays) : -1,
-                  plug_in->priv->images ?
-                  g_hash_table_size (plug_in->priv->images) : -1,
-                  plug_in->priv->items ?
-                  g_hash_table_size (plug_in->priv->items) : -1);
-#endif
-
-      gimp_plug_in_destroy_proxies (plug_in);
-    }
+  if (! plug_in->priv->procedure_stack)
+    gimp_plug_in_destroy_hashes (plug_in);
 }
 
 GimpDisplay *
@@ -1298,7 +1253,7 @@ _gimp_plug_in_get_display (GimpPlugIn *plug_in,
 
       g_hash_table_insert (plug_in->priv->displays,
                            GINT_TO_POINTER (display_id),
-                           display);
+                           g_object_ref (display) /* add debug ref */);
     }
 
   return display;
@@ -1330,7 +1285,7 @@ _gimp_plug_in_get_image (GimpPlugIn *plug_in,
 
       g_hash_table_insert (plug_in->priv->images,
                            GINT_TO_POINTER (image_id),
-                           image);
+                           g_object_ref (image) /* add debug ref */);
     }
 
   return image;
@@ -1390,16 +1345,76 @@ _gimp_plug_in_get_item (GimpPlugIn *plug_in,
       if (item)
         g_hash_table_insert (plug_in->priv->items,
                              GINT_TO_POINTER (item_id),
-                             item);
+                             g_object_ref (item) /* add debug ref */);
     }
 
   return item;
 }
 
 static void
-gimp_plug_in_destroy_proxies (GimpPlugIn *plug_in)
+gimp_plug_in_destroy_hashes (GimpPlugIn *plug_in)
 {
   g_clear_pointer (&plug_in->priv->displays, g_hash_table_unref);
   g_clear_pointer (&plug_in->priv->images,   g_hash_table_unref);
   g_clear_pointer (&plug_in->priv->items,    g_hash_table_unref);
 }
+
+static void
+gimp_plug_in_destroy_proxies (GHashTable *hash_table,
+                              gboolean    finalize)
+{
+  GHashTableIter iter;
+  gpointer       key, value;
+
+  if (! hash_table)
+    return;
+
+  g_hash_table_iter_init (&iter, hash_table);
+
+  while (g_hash_table_iter_next (&iter, &key, &value))
+    {
+      GObject *object = value;
+
+      if (object->ref_count == 2)
+        {
+          /* this is the normal case for an unused proxy */
+
+          g_object_unref (object);
+          g_hash_table_iter_remove (&iter);
+        }
+      else if (object->ref_count == 1)
+        {
+          /* this is debug code, a plug-in MUST NOT unref a proxy, we
+           * only catch one unref here, more then one will crash right
+           * in this function
+           */
+
+          gint id;
+
+          g_object_get (object, "id", &id, NULL);
+
+          g_printerr ("%s: ERROR: %s proxy with ID %d was unrefed "
+                      "by plug-in, it MUST NOT do that!\n",
+                      G_STRFUNC, G_OBJECT_TYPE_NAME (object), id);
+
+          g_hash_table_iter_remove (&iter);
+        }
+      else if (finalize)
+        {
+          /* this is debug code, a plug-in MUST NOT ref a proxy */
+
+          gint id;
+
+          g_object_get (object, "id", &id, NULL);
+
+          g_printerr ("%s: ERROR: %s proxy with ID %d was refed "
+                      "by plug-in, it MUST NOT do that!\n",
+                      G_STRFUNC, G_OBJECT_TYPE_NAME (object), id);
+
+          while (object->ref_count > 1)
+            g_object_unref (object);
+
+          g_hash_table_iter_remove (&iter);
+        }
+    }
+}