Method enqueue

kernel/oswrapper/vspace.h:1110–1114

      _lock() {
  }
  void enqueue(T item) {
    if (_bounded)
      _outgoing.wait();
    enqueue_nowait(item);
  }
  bool try_enqueue(T item) {
    if (_bounded && _outgoing.try_wait()) {
      enqueue_nowait(item);