getitimer.2 (2010 09)

g
getitimer(2) getitimer(2)
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 *value,
struct itimerval *ovalue
);
DESCRIPTION
The getitimer() function stores the current value of the timer specified by which into the structure
pointed to by value . The
setitimer() function sets the timer specified by which to the value specified
in the structure pointed to by value , and if ovalue is not a null pointer, stores the previous value of the
timer in the structure pointed to by ovalue .
The
<sys/time.h> header declares the itimerval structure:
struct timeval it_interval; /* timer interval */
struct timeval it_value; /* current value */
If it_value is non-zero, it indicates the time to the next timer expiration. If it_interval is non-zero, it
specifies a value to be used in reloading it_value when the timer expires. Setting it_value to 0 disables
the timer, regardless of the value of it_interval . Setting it_interval to 0 disables the 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 will be rounded up to the next supported value. Timer values smaller than the resolution of the
system clock are rounded up to this resolution. The machine-dependent clock resolution is 1 /
HZ seconds,
where the constant
HZ is defined in <sys/param.h>
. To make sure that a process gets at least as
much time as requested, the timer value is rounded up to the next timer tick (a timer tick is the smallest
supported value). The timer value is rounded up to the next timer tick, because the timer may be initial-
ized somewhere between timer ticks. If a
setitimer() is followed by a getitimer() without a
timer tick in between, it is possible that the value returned by getitimer() may be more than the ini-
tial value requested by setitimer() due to this rounding.
Implementations may place limitations on the timer value. Timer values larger than an implementation-
specific maximum value are rounded down to this maximum. The maximum values for the three interval
timers are specified by the constants
MAX_ALARM, MAX_VTALARM, and MAX_PROF defined in
<sys/param.h>. On all implementations, these values are guaranteed to be at least 31 days (in
seconds).
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 to the process
when this timer expires.
ITIMER_VIRTUAL Decrements in process virtual time. This timer runs only when the pro-
cess is executing. A SIGVTALRM signal is delivered to the process when
the timer expires.
ITIMER_PROF Decrements both in process virtual time and when the system is running
on behalf of the process. This timer is designed to be used by inter-
preters in statistically profiling the execution of interpreted programs.
Each time the ITIMER_PROF timer expires, a SIGPROF signal is
delivered to the process.
In addition to the above timers, HP-UX provides the following three per-thread interval timers for
PTHREAD_SCOPE_SYSTEM threads, which are indicated by the which argument:
ITIMER_THREAD_REAL Decrements in real time. A SIGALRM signal is delivered to the
thread which set this timer when the timer expires.
HP-UX 11i Version 3: September 2010 − 1 − Hewlett-Packard Company 1