static class Q implements AutoCloseable {

  S name = "Unnamed Queue";

  L<Runnable> q = synchroLinkedList();

  ReliableSingleThread rst = new(r { _run() });

  gettable volatile bool retired;

  gettable volatile Runnable currentJob;

  new AtomicLong jobsDone;

  *() {}

  *(S *name) {}

  void add(Runnable r) {

    assertNotRetired();

    q.add(r);

    _trigger();

  }

  void addInFront(Runnable r) {

    assertNotRetired();

    q.add(0, r);

    _trigger();

  }

  void _trigger() {

    rst.name = name;

    rst.go();

  }

  void add(O r) {

    add(toRunnable(r));

  }

  void _run() {

    Runnable r;

    while (licensed() && !retired && (r = syncPopFirst(q)) != null) {

      currentJob = r;

      inc(jobsDone);

      pcall { r.run(); }

      currentJob = null;

    }

    onIdle();

  }

  public void close() { retired = true; } // TODO: interrupt thread

  void done() {} // legacy function

  bool isEmpty() { ret q.isEmpty(); }

  int size() { ret q.size(); }

  O mutex() { ret q; } // clients can synchronize on this

  L<Runnable> snapshot() { ret cloneList(q); }

  // override this

  void onIdle {}

  bool busy() { ret currentJob != null; }

  void assertNotRetired() {

    assertFalse("Queue is retired", retired());

  }

  bool hasThread() { ret rst.hasThread(); }

  long nJobsDone() { ret jobsDone!; }

  toString {

    ret (retired ? "Retired " : "") + "Q " + systemHashCodeHex(this)

      + " (" + (isEmpty() ? "empty" : nEntries(size()) + ", current job: " + currentJob) + ")";

  }

}