HP-UX Reference (11i v1 00/12) - 2 System Calls (vol 5)

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getitimer(2) getitimer(2)

HP-UX EXTENSIONS

DESCRIPTION

A timer value is deﬁned by the itimerval structure:

struct itimerval {

struct timeval it_interval; /* timer interval */

struct timeval it_value; /* current value */

};

Time 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>. 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).

Each time the ITIMER_PROF timer expires, the SIGPROF signal is delivered. Since this signal can inter-

rupt 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>:

timerclear Set a time value to zero.

timerisset Test if a time value is non-zero.

timercmp Compare two time values. (Beware that >= and <= do not work with the

timercmp macro.)

The timer used with ITIMER_REAL is also used by alarm() (see alarm(2)). Thus successive calls to

alarm(), getitimer() , and setitimer() set and return the state of a single timer. In addition, a

call to alarm() sets the timer interval to zero.

ERRORS

getitimer() or setitimer() fail if any of the following conditions are encountered:

[EFAULT] The value structure speciﬁed a bad address. Reliable detection of this error is imple-

mentation dependent.

[EINVAL] A value structure speciﬁed a microsecond value less that zero or greater than or equal

to one million.

[EINVAL] which does not specify one of the three possible timers.

EXAMPLES

The following call to setitimer() sets the real-time interval timer to expire initially after 10 seconds

and every 0.5 seconds thereafter:

struct itimerval rttimer;

struct itimerval old_rttimer;

rttimer.it_value.tv_sec = 10;

rttimer.it_value.tv_usec = 0;

rttimer.it_interval.tv_sec = 0;

rttimer.it_interval.tv_usec = 500000;

setitimer (ITIMER_REAL, &rttimer, &old_rttimer);

AUTHOR

getitimer() was developed by the University of California, Berkeley.