Return the CPU time that has been consumed by this process or
thread. -1 is returned if the system couldn't determine it. The
time is normally returned in microseconds, but if the optional
argument nsec is nonzero it's returned in nanoseconds.
The CPU time includes both user and system time, i.e. it's
approximately the same thing you would get by adding together the
"utime" and "stime" fields returned by System.getrusage (but
perhaps with better accuracy).
It's however system dependent whether or not it's the time
consumed in all threads or in the current one only;
System.CPU_TIME_IS_THREAD_LOCAL tells which. If both types are
available then thread local time is preferred.