rl_q_cas
if (rl_q_cas(prev, cur, next)) {
if (rl_q_cas(prev, cur, next)) {
if (rl_q_cas(prev, cur, next)) {
if (cur == NULL && rl_q_cas(prev, NULL, e))
if (rl_q_cas(prev, cur, next)) {
if (rl_q_cas(prev, cur, e)) {