GETHRTIME(3C)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 settimeof‐
day(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 vir‐
tual 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 ALSOproc(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.
Sep 7, 2004 GETHRTIME(3C)
