sclass ManualTailFile extends TailFile {

  long lastCheck;

  Lock lock = lock();

  // onData: Runnable or voidfunc(S)

  *(final File *file, int *interval, fO *onData) {}

  *(final File *file, fO *onData) { interval = 100; }

  // updates in this thread

  void check() {

    long l2 = 0;

    {

      lock lock;

      long now = sysNow();

      if (now < lastCheck+interval) ret;

      lastCheck = now;

      l2 = l(file);

      if (l2 < l) l = 0; // file shrunk (log rotated!) - start over from beginning of file

      if (l2 == l) hasIdled = true;

      else pcall {

        if (debug) print("New data in " + f2s(file) + ": " + n2(l2-l, "byte"));

      }

    }

    // call onData outside of locked part

    for (S s : loadTextFilePart_iterator(file, l, l2))

      pcallF(onData, s);

    l = l2;

  }

}