void halt_zuruck(int s)
{
    signal(SIGKILL, SIG_DFL);
    signal(SIGINT, SIG_DFL);
    signal(SIGTERM, SIG_DFL);
    cerr << "halted with code " << s << " in thread " << omp_get_thread_num() << endl;

    kill(getpid(), SIGKILL);
}