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



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

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 indicate 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_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.

       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.

       The interaction between setitimer() and alarm() or sleep() 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
       Applications should use the timer__gettime() and timer__settime()
       functions instead of the obsolescent getitimer() and setitimer()
       functions, respectively.

RATIONALE
       None.

FUTURE DIRECTIONS
       The getitimer() and setitimer() functions may be removed in a future
       version.

SEE ALSO
       alarm(), exec, sleep(), timer__getoverrun()

       The Base Definitions volume of POSIX.1-2017, <signal.h>, <sys_time.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 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.opengroup.org/unix/online.html .

       Any typographical or formatting errors that appear in this page are
       most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .



IEEE/The Open Group                  2017                         GETITIMER(3)
