static String _computerID;
static Lock computerID_lock = lock();

public static String computerID() {
  if (_computerID == null) {
    lock computerID_lock;
    if (_computerID != null) ret _computerID;
    File file = computerIDFile();
    _computerID = loadTextFile(file.getPath());
    if (_computerID == null) {
      // legacy load
      _computerID = loadTextFile(userDir(".tinybrain/computer-id"));
      if (_computerID == null)
        _computerID = makeRandomID(12, new SecureRandom);
      saveTextFile(file, _computerID);
    }
  }
  ret _computerID;
}