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) + ")";
  }
}