1GETITIMER(3P)              POSIX Programmer's Manual             GETITIMER(3P)
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PROLOG

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

12       getitimer, setitimer — get and set value of interval timer
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SYNOPSIS

15       #include <sys/time.h>
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17       int getitimer(int which, struct itimerval *value);
18       int setitimer(int which, const struct itimerval *restrict value,
19           struct itimerval *restrict ovalue);
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DESCRIPTION

22       The getitimer() function shall store the current  value  of  the  timer
23       specified  by  which  into  the  structure  pointed  to  by value.  The
24       setitimer() function shall set the timer  specified  by  which  to  the
25       value  specified in the structure pointed to by value, and if ovalue is
26       not a null pointer, store the previous value of the timer in the struc‐
27       ture pointed to by ovalue.
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29       A  timer  value  is  defined  by  the itimerval structure, specified in
30       <sys/time.h>.  If it_value is non-zero, it shall indicate the  time  to
31       the  next timer expiration.  If it_interval is non-zero, it shall spec‐
32       ify a value to be used in reloading it_value when  the  timer  expires.
33       Setting it_value to 0 shall disable a timer, regardless of the value of
34       it_interval.  Setting it_interval to 0 shall disable a timer after  its
35       next expiration (assuming it_value is non-zero).
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37       Implementations  may place limitations on the granularity of timer val‐
38       ues. For each interval timer, if the requested timer value  requires  a
39       finer  granularity  than  the implementation supports, the actual timer
40       value shall be rounded up to the next supported value.
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42       An XSI-conforming implementation provides each process  with  at  least
43       three interval timers, which are indicated by the which argument:
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45       ITIMER_PROF   Decrements both in process virtual time and when the sys‐
46                     tem is running on behalf of the process. It  is  designed
47                     to be used by interpreters in statistically profiling the
48                     execution  of  interpreted  programs.   Each   time   the
49                     ITIMER_PROF  timer  expires, the SIGPROF signal is deliv‐
50                     ered.
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52       ITIMER_REAL   Decrements in real time. A SIGALRM  signal  is  delivered
53                     when this timer expires.
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55       ITIMER_VIRTUAL
56                     Decrements in process virtual time. It runs only when the
57                     process is executing. A  SIGVTALRM  signal  is  delivered
58                     when it expires.
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60       The  interaction between setitimer() and alarm() or sleep() is unspeci‐
61       fied.
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RETURN VALUE

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

68       The setitimer() function shall fail if:
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70       EINVAL The value argument is not in canonical form. (In canonical form,
71              the number of microseconds is a non-negative integer  less  than
72              1000000 and the number of seconds is a non-negative integer.)
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74       The getitimer() and setitimer() functions may fail if:
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76       EINVAL The which argument is not recognized.
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78       The following sections are informative.
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EXAMPLES

81       None.
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APPLICATION USAGE

84       Applications  should  use the timer_gettime() and timer_settime() func‐
85       tions instead of the obsolescent getitimer() and setitimer() functions,
86       respectively.
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RATIONALE

89       None.
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FUTURE DIRECTIONS

92       The  getitimer()  and  setitimer() functions may be removed in a future
93       version.
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SEE ALSO

96       alarm(), exec, sleep(), timer_getoverrun()
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98       The Base Definitions volume of POSIX.1‐2017, <signal.h>, <sys_time.h>
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101       Portions of this text are reprinted and reproduced in  electronic  form
102       from  IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
103       table Operating System Interface (POSIX), The Open Group Base  Specifi‐
104       cations  Issue  7, 2018 Edition, Copyright (C) 2018 by the Institute of
105       Electrical and Electronics Engineers, Inc and The Open Group.   In  the
106       event of any discrepancy between this version and the original IEEE and
107       The Open Group Standard, the original IEEE and The Open Group  Standard
108       is  the  referee document. The original Standard can be obtained online
109       at http://www.opengroup.org/unix/online.html .
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111       Any typographical or formatting errors that appear  in  this  page  are
112       most likely to have been introduced during the conversion of the source
113       files to man page format. To report such errors,  see  https://www.ker
114       nel.org/doc/man-pages/reporting_bugs.html .
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118IEEE/The Open Group                  2017                        GETITIMER(3P)
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