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Manual page for GETITIMER(2)

getitimer, setitimer - get/set value of interval timer

SYNOPSIS

#include <sys/time.h>

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

int 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 stores the current value of the timer specified by which into the structure pointed to by value. The setitimer() call sets the value of 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.

A timer value is defined by the itimerval structure, which includes the following members:

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 zero disables a timer; however, it_value and it_interval must still be initialized. Setting it_interval to zero 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 three timers are:

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 executing. 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 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.

RETURN VALUES

getitimer() and setitimer() return:

0: on success.
-1: on failure and set errno to indicate the error.

ERRORS

The possible errors are:

EFAULT: The value or ovalue parameter specified a bad address.
EINVAL: The value parameter specified a time that was too large to be handled.

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).