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GETITIMER(2)                  System Calls Manual                 GETITIMER(2)

NAME
     getitimer, setitimer - get/set value of interval timer

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <sys/time.h>

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

     int
     setitimer(int which, const struct itimerval * restrict value,
         struct itimerval * restrict ovalue);

DESCRIPTION
     The system provides each process with multiple interval timers, defined
     in <sys/time.h>.  The getitimer() call returns the current value for the
     timer specified in which in the structure at value.  The setitimer() call
     sets a timer to the specified value, returning the previous value of the
     timer if ovalue is not NULL.

     A timer value is defined by the itimerval structure:

           struct itimerval {
                   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.  Setting it_interval to 0 causes a timer to be disabled
     after its next expiration (assuming it_value is non-zero).

     The which parameter specifies the type of the timer:

           ITIMER_REAL        timer decrements in real time.  This timer is
                              affected by adjtime(2) and settimeofday(2).  A
                              SIGALRM signal is delivered when this timer
                              expires.

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

           ITIMER_PROF        timer 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 delivered.  Because this signal may
                              interrupt in-progress system calls, programs
                              using this timer must be prepared to restart
                              interrupted system calls.

           ITIMER_MONOTONIC   timer decrements in monotonic time.  This timer
                              is not affected by adjtime(2) and
                              settimeofday(2).  A SIGALRM signal is delivered
                              when this timer expires.
     Note that:

           ⊕   Time values smaller than the resolution of the system clock are
               rounded up to this resolution (typically 10 milliseconds).

           ⊕   The interaction between setitimer() and alarm(3) or sleep(3) is
               unspecified by the specification.

RETURN VALUES
     If the calls succeed, a value of 0 is returned.  If an error occurs, the
     value -1 is returned, and a more precise error code is placed in the
     global variable errno.

ERRORS
     Both functions may fail if:

     [EFAULT]           The value parameter specified a bad address.

     [EINVAL]           The which parameter was not a known timer type, or the
                        value parameter specified a time that was too large to
                        be handled.

SEE ALSO
     gettimeofday(2), select(2), sigaction(2), itimerval(3), timeradd(3)

STANDARDS
     The functions conform to IEEE Std 1003.1-2001 ("POSIX.1").  The later
     IEEE Std 1003.1-2008 ("POSIX.1") revision however marked both as
     obsolescent, recommending the use of timer_gettime(2) and
     timer_settime(2) instead.

HISTORY
     The getitimer() function call appeared in 4.2BSD.  The ITIMER_MONOTONIC
     functionality appeared in NetBSD 6.0.

NetBSD 10.99                    April 28, 2019                    NetBSD 10.99