For linux:

clock_gettime()

CLOCK_PROCESS_CPUTIME_ID

(since Linux 2.6.12)

This is a clock that measures CPU time consumed by this process (i.e., CPU time consumed by all threads in the process). On Linux, this clock is not settable.

CLOCK_THREAD_CPUTIME_ID

(since Linux 2.6.12)

This is a clock that measures CPU time consumed by this thread. On Linux, this clock is not settable.