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Defer GObject::notify during object destruction

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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
This commit is contained in:
Emmanuele Bassi 2021-11-28 00:36:06 +00:00
parent a8edd30355
commit 1ec331266a
1 changed files with 24 additions and 1 deletions
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25
gobject/gobject.c
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@ -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);
}
}
}