process.c:1290
static VALUE
p_sys_setreuid(obj, rid, eid)
    VALUE obj, rid, eid;
{
#if defined HAVE_SETREUID
    rb_secure(2);
    if (under_uid_switch) {
	rb_raise(rb_eRuntimeError, "can't handle UID during evaluating the block given to the Process::UID.switch method");
    }
    if (setreuid(NUM2INT(rid),NUM2INT(eid)) != 0) rb_sys_fail(0);
#else
    rb_notimplement();
#endif
    return Qnil;
}
