static O evalInNewThread(fO f) {
  final new Flag flag;
  final new Var var;
  final new Var<Throwable> exception;
  thread {
    try {
      var.set(callF(f));
    } catch e {
      exception.set(e);
    }
    flag.raise();
  }
  flag.waitUntilUp();
  if (exception.has()) throw rethrow(exception!);
  ret var!;
}