GETITIMER(2)                         BSD                          GETITIMER(2)



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

SYNOPSIS
     #include <sys/time.h>

     #define ITIMER_REAL      0    /* real time intervals */
     #define ITIMER_VIRTUAL   1    /* virtual time intervals */

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

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

DESCRIPTION
     The system provides each process with two 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.  (setitimer returns the previous value of
     the timer if ovalue is nonzero.)

     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 nonzero, it indicates the time to the next timer
     expiration. If it_interval is nonzero, 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 nonzero).

     Time values smaller than the resolution of the system clock (4
     microseconds on Domain/OS) are rounded up to this resolution.

     The ITIMER_REAL timer decrements in real time and delivers a SIGALRM
     signal when it expires.

     The ITIMER_VIRTUAL timer decrements in process virtual time.  It runs
     only when the process is executing and delivers a SIGVTALRM signal when
     it expires.

ERRORS
     The possible error is

     [EINVAL]   A value parameter specified a time was too large to be
                handled.

SEE ALSO
     sigvec(2), gettimeofday(2)

DIAGNOSTICS
     A successful call returns 0.  A failed call returns -1 and sets errno to
     indicate the error.

NOTES

     Three macros for manipulating time values are defined in <sys/time.h>.
     timerclear sets a time value to 0, timerisset tests if a time value is
     nonzero, and timercmp compares two time values (beware that >= and <= do
     not work with this macro).

     ITIMER_PROF, defined on some other implementations as

          #define ITIMER_PROF 2    /* user and system virtual time */

     is not supported under Domain/OS BSD.  On those implementations, the
     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 can interrupt in-progress system calls,
     programs using this timer must be prepared to restart interrupted system
     calls.

WARNINGS
     Excess signal activity may result from the use of very small it_interval
     values.