Updated: 2022/Sep/29

Please read Privacy Policy. It's for your privacy.

TIMEVAL(3)                 Library Functions Manual                 TIMEVAL(3)

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.

      1.   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.

      2.   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.

      3.   The following structure is used by setitimer(2), among others:

                 struct itimerval {
                         struct timeval  it_interval;
                         struct timeval  it_value;
                 };

      4.   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.

      5.   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)

NetBSD 10.99                    April 12, 2011                    NetBSD 10.99