getitimer(2)                                         getitimer(2)



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

     SYNOPSIS
          #include <sys/time.h>

          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 three interval timers,
          defined in <sys/time.h>.  The getitimer call returns the
          current value for the timer specified in which in the struc-
          ture at value.  The setitimer call sets a timer to the
          specified value (returning 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 ex-
          pires.  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
          are rounded up to this resolution (16 milliseconds on this
          system, 10 milliseconds on the VAX).

          The ITIMER_REAL timer decrements in real time.  A SIGALRM
          signal is delivered when this timer expires.

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

          The ITIMER_PROF timer decrements both in process virtual
          time and when the system is running on behalf of the pro-
          cess.  It is designed to be used by interpreters in statist-
          ically profiling the execution of interpreted programs.
          Each time the ITIMER_PROF timer expires, the SIGPROF signal



     April, 1990                                                     1

     getitimer(2)                                         getitimer(2)



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

     NOTES
          Three macros for manipulating time values are defined in
          <sys/time.h>.  timerclear sets a time value to zero, timer-
          isset tests if a time value is nonzero, and timercmp com-
          pares two time values (beware that >= and <= do not work
          with this macro).

     RETURN VALUE
          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
          The possible errors are:

          [EFAULT]       The value parameter specified a bad address.

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

     SEE ALSO
          sigvec(2), gettimeofday(2).





























     2                                                     April, 1990