itimerval(3) - NetBSD Manual Pages

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TIMEVAL(3)              NetBSD 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 nanosec-
           onds.

           A microsecond is equal to one millionth of a second, 1000 nanosec-
           onds, or 1/1000 milliseconds.  To ease the conversions, the macros
           TIMEVAL_TO_TIMESPEC() and TIMESPEC_TO_TIMEVAL() can be used to con-
           vert 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 indi-
           cates 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 struc-
     tures 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 8.2                      April 12, 2011                      NetBSD 8.2