sclass TailFile {
  int interval;
  long l;
  new Flag stopped;
  java.util.Timer timer;
  ReliableSingleThread thread;
  volatile bool hasIdled;
  
  *(final File file, int *interval, fO onData) {
    thread = new ReliableSingleThread(r {
      long l2 = l(file);
      if (l2 < l) l = 0;
      if (l2 == l) hasIdled = true;
      else pcall {
        S text = null;
        pcall {
          // TODO: load in parts
          text = loadTextFilePart(file, l, l2);
        }
        if (nempty(text))
          pcallF(onData, text);
        l = l2;
      }
    });
  }
  
  void start {
    timer = doEvery(interval, r {
      if (!stopped.isUp()) thread.trigger()
    });
  }
  
  void stop {
    timer.cancel();
    timer = null;
    if (stopped.raise())
      thread.triggerAndWait(); // One last time baby
  }
  
  bool started() {
    ret timer != null;
  }
}