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GETITIMER
Section: POSIX Programmer's Manual (3P)
Updated: 2003
Index
Return to Main Contents
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
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_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,
<signal.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, Copyright (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.opengroup.org/unix/online.html .
Index
- PROLOG
-
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- EXAMPLES
-
- APPLICATION USAGE
-
- RATIONALE
-
- FUTURE DIRECTIONS
-
- SEE ALSO
-
- COPYRIGHT
-
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