GETITIMER(2)

NAME

getitimer, setitimer − get/set value of interval timer

SYNOPSIS

#include <sys/time.h>

#define ITIMER_REAL   0   /* real time intervals */
#define ITIMER_VIRTUAL   1   /* virtual time intervals */
#define ITIMER_PROF   2   /* user and system virtual time */
getitimer(which, value)
int which;
struct itimerval *value;

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

HP-UX COMPATIBILITY

Level: HP-UX/STANDARD

Origin: UCB

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 {
structtimeval it_interval;/* timer interval */
structtimeval 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 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.

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.

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. Getitimer or setitimer can fail if:

[EFAULT] The value structure specified a bad address.

[EINVAL] A value structure specified an invalid time.

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

HARDWARE DEPENDENCIES

Series 500

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

[EINVAL] Call not allowed in [vfork,exec] window

Museum

Related Articles