CLOCK_REALTIME 0
CLOCK_MONOTONIC 1
CLOCK_PROCESS_CPUTIME_ID 2
CLOCK_THREAD_CPUTIME_ID 3
CLOCK_MONOTONIC_RAW 4
CLOCK_REALTIME_COARSE 5
CLOCK_MONOTONIC_COARSE 6
CLOCK_BOOTTIME 7
CLOCK_REALTIME_ALARM 8
CLOCK_BOOTTIME_ALARM 9
CLOCK_SGI_CYCLE 10
CLOCK_TAI 11