NAME
bintime,
getbintime,
microtime,
getmicrotime,
nanotime,
getnanotime —
get the current time
SYNOPSIS
#include <sys/time.h>
void
bintime(
struct bintime *bt);
void
getbintime(
struct bintime *bt);
void
microtime(
struct timeval *tv);
void
getmicrotime(
struct timeval *tv);
void
nanotime(
struct timespec *tsp);
void
getnanotime(
struct timespec *tsp);
DESCRIPTION
The
bintime() and
getbintime() functions
store the system time as a
struct bintime at the
addresses specified by
bt. The
microtime() and
getmicrotime() functions
perform the same utility, but record the time as a
struct
timeval instead. Similarly the
nanotime() and
getnanotime() functions store the time as a
struct timespec. The structures are described in
timeval(3).
The
bintime(),
microtime(), and
nanotime() functions always query the timecounter to return
the current time as precisely as possible. Whereas
getbintime(),
getmicrotime(), and
getnanotime() functions are abstractions which return a less
precise, but faster to obtain, time.
The intent of the
getbintime(),
getmicrotime(), and
getnanotime()
functions is to enforce the user's preference for timer accuracy versus
execution time. They should be used where a precision of
1/
HZ (e.g., 10 msec on a 100
HZ machine,
see
hz(9)) is acceptable or where
performance is priority.
The system realtime clock is guaranteed to be monotonically increasing at all
times. As such, all calls to these functions are guaranteed to return a system
time greater than or equal to the system time returned in any previous calls.
Comparable functions exist to retrieve the time elapsed since boot; see
microuptime(9).
CODE REFERENCES
The implementation of the
microtime() family of functions is
in
sys/kern/kern_tc.c as a part of the
timecounter(9) framework.
The implementation of the time counter sources used by the
timecounter(9) is machine
dependent, hence its location in the source code tree varies from architecture
to architecture.
SEE ALSO
settimeofday(2),
bintime_add(9),
inittodr(9),
time_second(9),
tvtohz(9)
AUTHORS
This manual page was written by
Jeremy Cooper and
Kelly Yancey
<
kbyanc@posi.net>.
CAVEATS
Despite the guarantee that the system realtime clock will always be
monotonically increasing, it is always possible for the system clock to be
manually reset by the system administrator to any date.