GETITIMER(3P)                                       POSIX Programmer's Manual                                      GETITIMER(3P)



PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (con-
       sult the corresponding Linux manual page for details of Linux behavior), or the  interface  may  not  be  implemented  on
       Linux.

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

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  getitimer()  function shall store the current value of the timer specified by which into the structure pointed to by
       value. The setitimer() function shall set the timer specified by which to the value specified in the structure pointed to
       by  value,  and  if  ovalue  is  not a null pointer, store the previous value of the timer in the structure pointed to by
       ovalue.

       A timer value is defined by the itimerval structure, specified in <sys/time.h>. If it_value is non-zero, it  shall  indi-
       cate  the time to the next timer expiration. If it_interval is non-zero, it shall specify a value to be used in reloading
       it_value when the timer expires. Setting it_value to 0 shall disable a timer, regardless of  the  value  of  it_interval.
       Setting it_interval to 0 shall disable 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 shall be rounded  up  to  the
       next supported value.

       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 expires.

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

       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 delivered.


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

RETURN VALUE
       Upon  successful  completion, getitimer() or setitimer() shall return 0; otherwise, -1 shall be returned and errno set to
       indicate the error.

ERRORS
       The setitimer() function shall 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 1000000 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.


       The following sections are informative.

EXAMPLES
       None.

APPLICATION USAGE
       None.

RATIONALE
       None.

FUTURE DIRECTIONS
       None.

SEE ALSO
       alarm(),  sleep(),  timer_getoverrun(),  ualarm(),  usleep(),  the Base Definitions volume of IEEE Std 1003.1-2001, <sig-
       nal.h>, <sys/time.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003  Edition,  Standard  for
       Information  Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copy-
       right (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any
       discrepancy  between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group
       Standard  is  the  referee   document.   The   original   Standard   can   be   obtained   online   at   http://www.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                                 GETITIMER(3P)