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Man Page Of gethrtime

题注:Man Page这里我辑录一些我在学习研究过程中关注过,应用过的,供自己参考,也希望可以见证自己的学习历程。

$ man gethrtime

Standard C Library Functions gethrtime(3C)

gethrtime, gethrvtime - get high resolution time


hrtime_t gethrtime(void);

hrtime_t gethrvtime(void);

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 hires 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. This function requires that micro state accounting be
enabled with the ptime utility (see proc(1)).

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

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++)
end = gethrtime();

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

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

| MT-Level | MT-Safe |

SunOS 5.8 Last change: 10 Apr 1997 1

Standard C Library Functions gethrtime(3C)

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

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.

SunOS 5.8 Last change: 10 Apr 1997 2

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By eygle on 2004-11-19 21:02 | Comments (0) | System | 1884 |

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