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  man pages->HP-UX 11i man pages -> setitimer (2)              


 getitimer(2)                                                   getitimer(2)

 NAME    [Toc]    [Back]
      getitimer, setitimer - get and set value of interval timer

 SYNOPSIS    [Toc]    [Back]
      #include <sys/time.h>

      int getitimer(int which, struct itimerval *value);

      int setitimer(
           int which,
           const struct itimerval *value,
           struct itimerval *ovalue

 DESCRIPTION    [Toc]    [Back]
      The getitimer() function stores the current value of the timer
      specified by which into the structure pointed to by value.  The
      setitimer() function sets the timer specified by which to the value
      specified in the structure pointed to by value, and if ovalue is not a
      null pointer, stores the previous value of the timer in the structure
      pointed to by ovalue.

      The <sys/time.h> header declares the itimerval structure:

           struct timeval  it_interval;  /* timer interval */
           struct timeval  it_value;     /* current value */

      If it_value is non-zero, it indicates the time to the next timer
      expiration.  If it_interval is non-zero, it specifies a value to be
      used in reloading it_value when the timer expires.  Setting it_value
      to 0 disables a timer, regardless of the value of it_interval.
      Setting it_interval to 0 disables a timer after its next expiration
      (assuming it_value is non-zero).

      Implementations may place limitations on the granularity of timer
      values.  For each interval timer, if the requested timer value
      requires a finer granularity than the implementation supports, the
      actual timer value will be rounded up to the next supported value.
      Time values smaller than the resolution of the system clock are
      rounded up to this resolution.  The machine-dependent clock resolution
      is 1/HZ seconds, where the constant HZ is defined in <sys/param.h>.
      To make sure that a process gets at least as much time as requested,
      the timer value is rounded up to the next timer tick (a timer tick is
      the smallest supported value).  The timer value is rounded up to the
      next timer tick, because the timer may be initialized somewhere
      between timer ticks.  If a setitimer() is followed by a getitimer()
      without a timer tick in between, it is possible that the value
      returned by getitimer() may be more than the initial value requested
      by setitimer() due to this rounding.

 Hewlett-Packard Company            - 1 -   HP-UX 11i Version 2: August 2003

 getitimer(2)                                                   getitimer(2)

      Implementations may place limitations on the timer value.  Time values
      larger than an implementation-specific maximum value are rounded down
      to this maximum.  The maximum values for the three interval timers are
      specified by the constants MAX_ALARM, MAX_VTALARM, and MAX_PROF
      defined in <sys/param.h>.  On all implementations, these values are
      guaranteed to be at least 31 days (in seconds).

      An XSI-conforming implementation provides each process with at least
      three interval timers, which are indicated by the which argument:

           ITIMER_REAL              Decrements in real time.  A SIGALRM
                                    signal is delivered when this timer

           ITIMER_VIRTUAL           Decrements in process virtual time.  It
                                    runs only when the process is executing.
                                    A SIGVTALRM signal is delivered when it

           ITIMER_PROF              Decrements both in process virtual time
                                    and when the system is running on behalf
                                    of the process.  It is designed to be
                                    used by interpreters in statistically
                                    profiling the execution of interpreted
                                    programs.  Each time the ITIMER_PROF
                                    timer expires, the SIGPROF signal is

      Since SIGPROF signal can interrupt in-progress system calls, programs
      using this timer must be prepared to restart interrupted system calls.

      Interval timers are not inherited by a child process across a fork(),
      but are inherited across an exec().

      Three macros for manipulating time values are defined in <sys/time.h>:

           timerclear        Set a time value to zero.

           timerisset        Test if a time value is non-zero.

           timercmp          Compare two time values.  (Beware that >= and
                             <= do not work with the timercmp macro.)

      The timer used with ITIMER_REAL is also used by alarm() (see
      alarm(2)).  Thus successive calls to alarm(), getitimer(), and
      setitimer() set and return the state of a single timer.  In addition,
      a call to alarm() sets the timer interval to zero.

      The interaction between setitimer() and any of alarm(), sleep() or
      usleep() is unspecified.

 Hewlett-Packard Company            - 2 -   HP-UX 11i Version 2: August 2003

 getitimer(2)                                                   getitimer(2)

 RETURN VALUE    [Toc]    [Back]
      Upon successful completion, getitimer() or setitimer() returns 0.
      Otherwise, -1 is returned and errno is set to indicate the error.

 ERRORS    [Toc]    [Back]
      The setitimer() function will fail if:

            [EINVAL]      The value argument is not in canonical form.  (In
                          canonical form, the number of microseconds is a
                          non-negative integer less than 1,000,000 and the
                          number of seconds is a non-negative integer.)

      The getitimer() and setitimer() functions may fail if:

            [EINVAL]      The which argument is not recognized.

            [EFAULT]      The value structure specified a bad address.
                          Reliable detection of this error is implementation

 EXAMPLES    [Toc]    [Back]
      The following call to setitimer() sets the real-time interval timer to
      expire initially after 10 seconds and every 0.5 seconds thereafter:

           struct itimerval rttimer;
           struct itimerval old_rttimer;

           rttimer.it_value.tv_sec     = 10;
           rttimer.it_value.tv_usec    = 0;
           rttimer.it_interval.tv_sec  = 0;
           rttimer.it_interval.tv_usec = 500000;

           setitimer (ITIMER_REAL, &rttimer, &old_rttimer);

 AUTHOR    [Toc]    [Back]
      getitimer() was developed by the University of California, Berkeley.

 SEE ALSO    [Toc]    [Back]
      alarm(2), sleep(3C), ualarm(2), usleep(2), exec(2), signal(5).

 CHANGE HISTORY    [Toc]    [Back]
      First released in Issue 4, Version 2.

 Hewlett-Packard Company            - 3 -   HP-UX 11i Version 2: August 2003
[ Back ]
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