getitimer, setitimer - Return or set the value of interval
timers
#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 );
Interfaces documented on this reference page conform to
industry standards as follows:
getitimer(), setitimer(): XSH4.2, XSH5.0
Refer to the standards(5) reference page for more information
about industry standards and associated tags.
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.
The getitimer() function returns the current value for the
timer specified by the which parameter in the structure
pointed to by the value parameter.
The setitimer() function sets the timer specified by which
to the specified 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 SIGPROF signal is delivered. Because this
signal may interrupt in-progress system calls, programs
using this timer must be prepared to restart interrupted
system calls.
The following information applies only to the backwardcompatible
versions 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.
Upon successful completion, the value 0 (zero) is
returned. Otherwise, -1 is returned and errno is set to
indicate the error.
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.
Functions: gettimeofday(2)
Standards: standards(5)
getitimer(2)
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