FUTEX_CLOCK_REALTIME
const clockid_t clkid = (op & FUTEX_CLOCK_REALTIME) ? CLOCK_REALTIME
(~(FUTEX_PRIVATE_FLAG|FUTEX_CLOCK_REALTIME))
op |= FUTEX_CLOCK_REALTIME;
if (op & FUTEX_CLOCK_REALTIME) {
op &= ~FUTEX_CLOCK_REALTIME;