GETITIMER(2) — HP-UX

NAME

getitimer, setitimer − get/set value of interval timer

SYNOPSIS

#include <sys/time.h>

getitimer(which, value)
int which;
struct itimerval *value;

setitimer(which, value, ovalue)
int which;
struct itimerval *value, *ovalue;

DESCRIPTION

The system provides each process with three interval timers, defined in <sys/time.h>. The getitimer call returns the current value for the timer specified in which, while the setitimer call sets the value of a timer (optionally returning the previous value of the timer).

A timer value is defined by the itimerval structure:

struct itimerval {

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. Setting it_interval to 0 causes a timer to be disabled after its next expiration (assuming it_value is non-zero).

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).

The _which_ parameter specifies which timer to use. The possible values are ITIMER_REAL, ITIMER_VIRTUAL, and ITIMER_PROF.

The ITIMER_REAL timer decrements in real time. A SIGALRM signal is delivered when this timer expires.

The ITIMER_VIRTUAL timer decrements in process virtual time. It runs only when the process is executing. A SIGVTALRM signal is delivered when it expires.

The ITIMER_PROF timer 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.

Interval timers are not inherited by a child process across a fork, but are inherited across an exec.

NOTES

Three macros for manipulating time values are defined in <sys/time.h>. Timerclear sets a time value to zero, timerisset tests if a time value is non-zero, and timercmp compares two time values (beware that >= and <= do not work with this macro).

The timer used with ITIMER_REAL. is the same as that used by alarm(2). Thus successive calls to alarm, getitimer, and setitimer will set and return the state of a single timer.

EXAMPLES

The following call to setitimer(2) 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);

HARDWARE DEPENDENCIES

Series 500:
An error is generated if a call is made to getitimer or setitimer in the [vfork, exec] window.

RETURN VALUE

If the calls succeed, a value of 0 is returned. If an error occurs, the value −1 is returned, and a more precise error code is placed in the global variable errno.

ERRORS

Getitimer or setitimer can fail if:

[EFAULT] The value structure specified a bad address. The reliable detection of this error will be implementation 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.

AUTHOR

Getitimer was developed by the University of California, Berkeley California, Computer Science Division, Department of Electrical Engineering and Computer Science.

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