NAME
timeval,
timespec,
itimerval,
itimerspec,
bintime —
time structures
SYNOPSIS
#include <sys/time.h>
void
TIMEVAL_TO_TIMESPEC(
struct
timeval *tv,
struct
timespec *ts);
void
TIMESPEC_TO_TIMEVAL(
struct
timeval *tv,
struct
timespec *ts);
DESCRIPTION
The
<sys/time.h> header, included by
<time.h>, defines various structures
related to time and timers.
- The following structure is used by
gettimeofday(2), among
others:
struct timeval {
time_t tv_sec;
suseconds_t tv_usec;
};
The tv_sec member represents the elapsed time, in
whole seconds. The tv_usec member captures rest of
the elapsed time, represented as the number of microseconds.
- The following structure is used by
nanosleep(2), among
others:
struct timespec {
time_t tv_sec;
long tv_nsec;
};
The tv_sec member is again the elapsed time in whole
seconds. The tv_nsec member represents the rest of
the elapsed time in nanoseconds.
A microsecond is equal to one millionth of a second, 1000 nanoseconds, or
1/1000 milliseconds. To ease the conversions, the macros
TIMEVAL_TO_TIMESPEC() and
TIMESPEC_TO_TIMEVAL() can be used to convert between
struct timeval and struct
timespec.
- The following structure is used by
setitimer(2), among
others:
struct itimerval {
struct timeval it_interval;
struct timeval it_value;
};
- The following structure is used by
timer_settime(2),
among others:
struct itimerspec {
struct timespec it_interval;
struct timespec it_value;
};
Both struct itimerval and struct
itimerspec are used to specify when a timer expires. Generally,
it_interval specifies the period between successive
timer expirations. A value zero implies that the alarm will fire only
once. If it_value is non-zero, it indicates the time
left to the next timer expiration. A value zero implies that the timer is
disabled.
- The following structure is used by
bintime(9), among others:
struct bintime {
time_t sec;
uint64_t frac;
};
The sec member specifies the time in seconds and
frac represents a 64-bit fraction of seconds. The
struct bintime is meant to be used in the kernel
only. It is further described in
timecounter(9).
EXAMPLES
It can be stressed that the traditional UNIX
timeval and
timespec structures represent elapsed time, measured by
the system clock (see
hz(9)). The
following sketch implements a function suitable for use in a context where the
timespec structure is required for a conditional
timeout:
static void
example(struct timespec *spec, time_t minutes)
{
struct timeval elapsed;
(void)gettimeofday(&elapsed, NULL);
_DIAGASSERT(spec != NULL);
TIMEVAL_TO_TIMESPEC(&elapsed, spec);
/* Add the offset for timeout in minutes. */
spec->tv_sec = spec->tv_sec + minutes * 60;
}
A better alternative would use the more precise
clock_gettime(2).
SEE ALSO
timeradd(3),
tm(3),
bintime_add(9)