eval.c:9047
static VALUE
rb_thread_join_m(argc, argv, thread)
    int argc;
    VALUE *argv;
    VALUE thread;
{
    VALUE limit;
    double delay = DELAY_INFTY;
    rb_thread_t th = rb_thread_check(thread);

    rb_scan_args(argc, argv, "01", &limit);
    if (!NIL_P(limit)) delay = rb_num2dbl(limit);
    if (!rb_thread_join(th, delay))
	return Qnil;
    return thread;
}
