[glib/ebassi/dispose-notify: 5/5] Defer GObject::notify during object destruction
- From: Emmanuele Bassi <ebassi src gnome org>
- To: commits-list gnome org
- Cc:
- Subject: [glib/ebassi/dispose-notify: 5/5] Defer GObject::notify during object destruction
- Date: Mon, 29 Nov 2021 15:44:56 +0000 (UTC)
commit 1ec331266ac5782223d3dafa6c9176eaeefcebae
Author: Emmanuele Bassi <ebassi gnome org>
Date: Sun Nov 28 00:36:06 2021 +0000
Defer GObject::notify during object destruction
Notifying during object destruction is a dubious "feature": objects
might end up recreating a bunch of state just before clearing it;
language bindings might get spurious notifications during garbage
collection runs.
We freeze the notification queue before running the dispose() chain; if
the object was temporarily vivified during dispose, we thaw the
notification queue, otherwise we let the instance clear it when we
finalize it.
See: https://gitlab.gnome.org/GNOME/gjs/-/issues/445
gobject/gobject.c | 25 ++++++++++++++++++++++++-
1 file changed, 24 insertions(+), 1 deletion(-)
---
diff --git a/gobject/gobject.c b/gobject/gobject.c
index 1c95e3d0d..2a75433da 100644
--- a/gobject/gobject.c
+++ b/gobject/gobject.c
@@ -303,6 +303,7 @@ g_object_notify_queue_freeze (GObject *object,
G_OBJECT_TYPE_NAME (object), object);
else
nqueue->freeze_count++;
+
G_UNLOCK(notify_lock);
return nqueue;
@@ -3574,6 +3575,7 @@ g_object_unref (gpointer _object)
else
{
GSList **weak_locations;
+ GObjectNotifyQueue *nqueue;
/* The only way that this object can live at this point is if
* there are outstanding weak references already established
@@ -3615,6 +3617,18 @@ g_object_unref (gpointer _object)
g_rw_lock_writer_unlock (&weak_locations_lock);
}
+ /* freeze the notification queue, so we don't accidentally emit
+ * notifications during dispose() and finalize().
+ *
+ * The notification queue stays frozen unless the instance acquires
+ * a reference during dispose(), in which case we thaw it and
+ * dispatch all the notifications. If the instance gets through
+ * to finalize(), the notification queue gets automatically
+ * drained when g_object_finalize() is reached and
+ * the qdata is cleared.
+ */
+ nqueue = g_object_notify_queue_freeze (object, FALSE);
+
/* we are about to remove the last reference */
TRACE (GOBJECT_OBJECT_DISPOSE(object,G_TYPE_FROM_INSTANCE(object), 1));
G_OBJECT_GET_CLASS (object)->dispose (object);
@@ -3631,6 +3645,9 @@ g_object_unref (gpointer _object)
if (!g_atomic_int_compare_and_exchange ((int *)&object->ref_count, old_ref, old_ref - 1))
goto retry_atomic_decrement2;
+ /* emit all notifications that have been queued during dispose() */
+ g_object_notify_queue_thaw (object, nqueue);
+
TRACE (GOBJECT_OBJECT_UNREF(object,G_TYPE_FROM_INSTANCE(object),old_ref));
/* if we went from 2->1 we need to notify toggle refs if any */
@@ -3657,7 +3674,6 @@ g_object_unref (gpointer _object)
{
TRACE (GOBJECT_OBJECT_FINALIZE(object,G_TYPE_FROM_INSTANCE(object)));
G_OBJECT_GET_CLASS (object)->finalize (object);
-
TRACE (GOBJECT_OBJECT_FINALIZE_END(object,G_TYPE_FROM_INSTANCE(object)));
GOBJECT_IF_DEBUG (OBJECTS,
@@ -3675,6 +3691,13 @@ g_object_unref (gpointer _object)
});
g_type_free_instance ((GTypeInstance*) object);
}
+ else
+ {
+ /* The instance acquired a reference between dispose() and
+ * finalize(), so we need to thaw the notification queue
+ */
+ g_object_notify_queue_thaw (object, nqueue);
+ }
}
}
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