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getitimer(2) getitimer(2)

NAME

getitimer, setitimer - get/set value of interval timer

SYNOPSIS

#include <sys/time.h>

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

int setitimer(

int which,

const struct itimerval *value,

struct itimerval *ovalue

);

DESCRIPTION

The getitimer() function stores the current value of the timer speciﬁed by which into the structure

pointed to by value. The setitimer() function sets 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. 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, regardless of the value of it_interval. Setting

it_interval to 0 disables a timer after its next expiration (assuming it_value is non-zero).

Implementations may place limitations on the granularity of timer values. For each interval timer, if the

requested timer value requires a ﬁner granularity than the implementation supports, the actual timer

value will be rounded up to the next supported value.

Implementations may place limitations on the timer value. To make sure that a process gets at least as

much time as requested, the timer value is rounded up to the next timer tick (a timer tick is the smallest

supported value). The timer value is rounded up to the next timer tick because, the timer will be initialize

somewhere between timer ticks. If a

setitimer() is followed by a getitimer() without a timer tick

in between, it is possible that the value returned by getitimer() may be more than the initial value

requested by

setitimer() due to this rounding.

An XSI-conforming implementation provides each process with at least three interval timers, which are

indicated by the which argument:

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 exe-

cuting. 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 statisti-

cally proﬁling the execution of interpreted programs.

The interaction between setitimer() and any of alarm(), sleep() or usleep() is unspeciﬁed.

RETURN VALUE

Upon successful completion, getitimer() or setitimer() returns 0. Otherwise, −1 is returned and

errno is set to indicate the error.

ERRORS

The setitimer() function will fail if:

[EINVAL] The value argument is not in canonical form.(In canonical form, the number of

microseconds is a non-negative integer less than 1,000,000 and the number of seconds

is a non-negative integer.)

The getitimer() and setitimer() functions may fail if:

[EINVAL] The which argument is not recognized.