void test_condition_wait_until_pred() {
    boost::fibers::fiber( boost::fibers::launch::dispatch, & do_test_condition_wait_until_pred).join();
    do_test_condition_wait_until_pred();
}
void test_condition_wait_until_pred() {
    boost::fibers::fiber( & do_test_condition_wait_until_pred).join();
    do_test_condition_wait_until_pred();
}