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
settimeofday(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\n", (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 guaranteed 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 adjustment, like the
time of day can), but not necessarily unique: two sufficiently proximate
calls may return the same value.


September 7, 2004 GETHRTIME(3C)