PIPE_WANTR
if (rpb->state & PIPE_WANTR) {
rpb->state &= ~PIPE_WANTR;
if (wpb->state & PIPE_WANTR) {
wpb->state &= ~PIPE_WANTR;
if (rpb->state & (PIPE_WANTR | PIPE_WANTW)) {
rpb->state &= ~(PIPE_WANTR | PIPE_WANTW);
if (wpb->state & (PIPE_WANTR | PIPE_WANTW)) {
wpb->state &= ~(PIPE_WANTR | PIPE_WANTW);
atomic_set_int(&rpb->state, PIPE_WANTR);
pipesignal(wpb, PIPE_WANTR);
pipesignal(wpb, PIPE_WANTR);
pipesignal(wpb, PIPE_WANTR);
pipesignal(wpb, PIPE_WANTR);