getitimer(2)getitimer(2)NAME
getitimer, setitimer - Return or set the value of interval timers
SYNOPSIS
#include <sys/time.h>
int getitimer(
int which,
struct itimerval *value ); int setitimer(
int which,
const struct itimerval *value,
struct itimerval *ovalue );
The following definition of the setitimer() function does not conform
to current standards and is supported only for backward compatibility:
int setitimer(
int which,
struct itimerval *value,
struct itimerval *ovalue );
STANDARDS
Interfaces documented on this reference page conform to industry stan‐
dards as follows:
getitimer(), setitimer(): XSH4.2, XSH5.0
Refer to the standards(5) reference page for more information about
industry standards and associated tags.
PARAMETERS
Identifies the interval timer. This parameter may be expressed as one
of three symbolic constants: ITIMER_REAL, ITIMER_VIRTUAL, and
ITIMER_PROF. Points to an itimerval structure whose members specify a
timer interval and the time left to the end of the interval. Points to
an itimerval structure whose members specify a current timer interval
and the time left to the end of the interval.
DESCRIPTION
The getitimer() function returns the current value for the timer speci‐
fied by the which parameter in the structure pointed to by the value
parameter.
The setitimer() function sets the timer specified by which to the spec‐
ified value (returning the previous value of the timer if ovalue is
nonzero).
A timer value is defined by the itimerval structure:
struct itimerval {
struct timeval it_interval;
struct timeval it_value; };
If the it_value field is nonzero, it indicates the time to the next
timer expiration. If the it_interval field is nonzero, it specifies a
value to be used in reloading it_value when the timer expires. Setting
it_value to 0 (zero) disables a timer. Setting it_interval to 0 causes
a timer to be disabled after its next expiration (assuming it_value is
nonzero).
Time values smaller than the resolution of the system clock are rounded
up to this resolution.
The system provides each process with three interval timers, defined in
the <sys/time.h> header file: Decrements in real time. A SIGALRM signal
is delivered when this timer expires. Decrements in process virtual
time. It runs only when the process is executing. A SIGVTALRM signal is
delivered when it expires. 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 SIG‐
PROF signal is delivered. Because this signal may interrupt in-progress
system calls, programs using this timer must be prepared to restart
interrupted system calls.
NOTES
The following information applies only to the backward-compatible ver‐
sions of the getitimer() and setitimer() functions.
Three macros for manipulating time values are defined in the
<sys/time.h> header file. The timerclear() macro sets a time value to
zero, the timerisset() macro tests if a time value is nonzero, and the
timercmp() macro compares two time values. Beware that the comparisons
>= and <= do not work with the timercmp() macro.
RETURN VALUES
Upon successful completion, the value 0 (zero) is returned. Otherwise,
-1 is returned and errno is set to indicate the error.
ERRORS
The setitimer() function sets errno to the specified values for the
following conditions: [Tru64 UNIX] The value parameter specified a bad
address. The value parameter specified a time that was too large to be
handled, or was a negative time value, or the which value is not
defined.
The getitimer() function sets errno to the specified values for the
following conditions: [Tru64 UNIX] The value parameter specified a bad
address. The which value is not defined.
[Tru64 UNIX] The value parameter specified a time that was too
large to be handled.
SEE ALSO
Functions: gettimeofday(2)
Standards: standards(5)getitimer(2)
