Persistents Representing Async Activity

v8

// src/global-handles.cc
void GlobalHandles::IterateAllRootsWithClassIds(ObjectVisitor* v) {
  for (NodeIterator it(this); !it.done(); it.Advance()) {
    if (it.node()->IsRetainer() && it.node()->has_wrapper_class_id()) {
      v->VisitEmbedderReference(it.node()->location(),
                                it.node()->wrapper_class_id());
    }
  }
}

source in chromium code search