Note that we have two calls
g_datalist_id_set_data (&object->qdata, quark_weak_notifies, NULL);
that don't take OPTIONAL_BIT_LOCK_WEAK_REFS lock. One is right before
finalize(). At that point, no other thread can hold a reference to the
object to race. One call is from g_object_real_dispose(). At this point,
theoretically the object could have been resurrected and a pointer
passed to another thread, so it can race against g_object_weak_ref()
and g_object_weak_unref().
Fix that, by performing all operations on the WeakRefStack while holding
the GData lock. By using g_datalist_id_update_atomic(), we no longer
need the OPTIONAL_BIT_LOCK_WEAK_REFS lock. On the other hand, we might
now do slightly more work while holding the GData lock.
Also, during g_object_weak_unref() free the WeakRefStack, if there
are no more references.
fbfccb70f8