HP-UX Reference (11i v2 03/08) - 2 System Calls (vol 5)

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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 a

timer, regardless of the value of it_interval . Setting it_interval to 0 disables a timer after its next expira-

tion (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. Time values smaller than the resolution of the sys-

tem 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. Time 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 when this timer

expires.

ITIMER_VIRTUAL Decrements in process virtual time. It runs only when the process is exe-

cuting. 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 sta-

tistically proﬁling the execution of interpreted programs. Each time the

ITIMER_PROF timer expires, the SIGPROF signal is delivered.

Since SIGPROF signal can interrupt in-progress system calls, programs using this timer must be

prepared to restart interrupted system calls.

Interval timers are not inherited by a child process across a

fork(), but are inherited across an

exec().

Three macros for manipulating time values are deﬁned in <

sys/time.h>:

Section 2−−94 Hewlett-Packard Company − 1 − HP-UX 11i Version 2: August 2003