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
Thebintime()
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 100HZ 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.