man pages section 3: Basic Library Functions

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Updated: July 2014
 
 

gethrvtime(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.