Reference

getitimer(2)

get/set value of interval timer

NAME

getitimer, setitimer – get/set value of interval timer

SYNOPSIS

#include <sys/time.h>

#define ITIMER_REAL 0

#define ITIMER_VIRTUAL 1

#define ITIMER_PROF 2

int

getitimer(int which, struct itimerval *value);

int

setitimer(int which, const struct itimerval *restrict value, struct itimerval *restrict 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 in the structure at value. The setitimer() call sets a timer to the specified value (returning the previous value of the timer if ovalue is non-nil).

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 (typically 10 milliseconds).

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).

RETURN VALUES

Upon successful completion, a value of 0 is returned. Otherwise, a value of -1 is returned and the global integer variable errno is set to indicate the error.

ERRORS

getitimer() and setitimer() will fail if:

[EFAULT]

The value parameter specified a bad address.

[EINVAL]

The value parameter specified a time that was too large to be handled or not in the canonical form.

[EINVAL]

The which parameter was invalid.

SEE ALSO

gettimeofday(2), select(2), sigaction(2)

HISTORY

The getitimer() function call appeared in 4.2BSD.

History