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 (consult 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 struc‐
ture 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 spec‐
ify 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 val‐
ues. 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 sys‐
tem 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 deliv‐
ered.
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 unspeci‐
fied.
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() func‐
tions 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 ALSOalarm(), exec, sleep(), timer_getoverrun()
The Base Definitions volume of POSIX.1‐2008, <signal.h>, <sys_time.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
cal and Electronics Engineers, Inc and The Open Group. (This is
POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/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.ker‐
nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 GETITIMER(3P)
