getitimer.2 (2010 09)

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getitimer(2) getitimer(2)

ITIMER_THREAD_VIRTUAL

Decrements in thread virtual time. This timer runs only when the

thread is executing. A

SIGVTALRM signal is delivered to the

thread which set this timer when the timer expires.

ITIMER_THREAD_PROF

Decrements both in thread virtual time and when the system is

running on behalf of the thread. Each time the

ITIMER_THREAD_PROF

timer expires, a SIGPROF signal is

delivered to the thread which set this timer.

Since a

SIGPROF signal can interrupt in-progress system calls, programs using this timer must be

prepared to restart the interrupted system call.

Interval timers are not inherited by a child process across a

fork(), but are inherited across an

exec().

Three macros for manipulating time values are deﬁned in

<sys/time.h>:

timerclear Set a time value to zero.

timerisset Test if a time value is non-zero.

timercmp Compare two time values. (Beware that >=

and <= do not work with the

timercmp macro.)

The timer used with

ITIMER_REAL is also used by alarm() (see alarm (2)). Thus successive calls to

alarm(), getitimer(), and setitimer() set and return the state of a single timer. In addition, a

call to alarm() sets the timer interval to zero.

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.

[EFAULT] The value structure speciﬁed a bad address. Reliable detection of this error is

implementation dependent.

EXAMPLES

The following call to

setitimer() 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);

AUTHOR

getitimer() was developed by the University of California, Berkeley.