GETITIMER(2)                                                      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 */
       #define ITIMER_PROF      2    /* user and system virtual time */

       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
       <_s_y_s_/_t_i_m_e_._h>.  The _g_e_t_i_t_i_m_e_r call returns the  current  value  for  the
       timer specified in _w_h_i_c_h in the structure at _v_a_l_u_e.  The _s_e_t_i_t_i_m_e_r call
       sets a timer to the specified _v_a_l_u_e (returning the  previous  value  of
       the timer if _o_v_a_l_u_e is nonzero).

       A timer value is defined by the _i_t_i_m_e_r_v_a_l structure:

              struct itimerval {
                   struct    timeval it_interval;     /* timer interval */
                   struct    timeval it_value;   /* current value */
              };

       If  _i_t__v_a_l_u_e is non-zero, it indicates the time to the next timer expi‐
       ration.  If _i_t__i_n_t_e_r_v_a_l is non-zero, it specifies a value to be used in
       reloading  _i_t__v_a_l_u_e when the timer expires.  Setting _i_t__v_a_l_u_e to 0 dis‐
       ables a timer.  Setting _i_t__i_n_t_e_r_v_a_l to 0 causes a timer to be  disabled
       after its next expiration (assuming _i_t__v_a_l_u_e is non-zero).

       Time values smaller than the resolution of the system clock are rounded
       up to this resolution (on the VAX, 10 milliseconds).

       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 process.  It is designed  to  be
       used by interpreters in statistically profiling the execution of inter‐
       preted 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.

NOTES
       Three  macros for manipulating time values are defined in <_s_y_s_/_t_i_m_e_._h>.
       _T_i_m_e_r_c_l_e_a_r sets a time value to zero, _t_i_m_e_r_i_s_s_e_t tests if a time  value
       is  non-zero, and _t_i_m_e_r_c_m_p compares 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 _e_r_r_n_o.

ERRORS
       The possible errors are:

       [EFAULT]       The _v_a_l_u_e parameter specified a bad address.

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

SEE ALSO
       sigvec(2), gettimeofday(2)



4.2 Berkeley Distribution       August 26, 1985                   GETITIMER(2)