freebsd man page for gethrtime

gethrtime(3C)						   Standard C Library Functions 					     gethrtime(3C)

NAME
       gethrtime, gethrvtime - get high resolution time

SYNOPSIS
       #include <sys/time.h>

       hrtime_t gethrtime(void);

       hrtime_t gethrvtime(void);

DESCRIPTION
       The  gethrtime()  function returns the current high-resolution real time. Time is expressed as nanoseconds since some arbitrary time in the
       past; it is not correlated in any way to the time of day, and thus is not subject to resetting or drifting by way of adjtime(2) or settime-
       ofday(3C). The hi-res timer is ideally suited to performance measurement tasks, where cheap, accurate interval timing is required.

       The gethrvtime() function returns the current high-resolution LWP virtual time, expressed as total nanoseconds of execution time.

       The gethrtime() and gethrvtime() functions both return an hrtime_t, which is a 64-bit (long long) signed integer.

EXAMPLES
       The following code fragment measures the average cost of getpid(2):

       hrtime_t start, end;
       int i, iters = 100;

       start = gethrtime();
       for (i = 0; i < iters; i++)
	       getpid();
       end = gethrtime();

       printf("Avg getpid() time = %lld nsec
", (end - start) / iters);

ATTRIBUTES
       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |MT-Level		     |MT-Safe			   |
       +-----------------------------+-----------------------------+

SEE ALSO
       proc(1), adjtime(2), gettimeofday(3C), settimeofday(3C), attributes(5)

NOTES
       Although  the  units of hi-res time are always the same (nanoseconds), the actual resolution is hardware dependent.  Hi-res time is guaran-
       teed to be monotonic (it won't go backward, it won't periodically wrap) and linear (it won't occasionally speed up or slow down for adjust-
       ment, like the time of day can), but not necessarily unique: two sufficiently proximate calls may return the same value.

SunOS 5.10							    7 Sep 2004							     gethrtime(3C)