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GETITIMER(2) Linux Programmer’s Manual GETITIMER(2)
NAME
getitimer, setitimer - get or set value of an 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 system provides each process with three interval timers, each decrementing in a
distinct time domain. When any timer expires, a signal is sent to the process, and
the timer (potentially) restarts.
ITIMER_REAL decrements in real time, and delivers SIGALRM upon expiration.
ITIMER_VIRTUAL decrements only when the process is executing, and delivers SIGV-
TALRM upon expiration.
ITIMER_PROF decrements both when the process executes and when the system is
executing on behalf of the process. Coupled with ITIMER_VIRTUAL,
this timer is usually used to profile the time spent by the applica-
tion in user and kernel space. SIGPROF is delivered upon expira-
tion.
Timer values are defined by the following structures:
struct itimerval {
struct timeval it_interval; /* next value */
struct timeval it_value; /* current value */
};
struct timeval {
long tv_sec; /* seconds */
long tv_usec; /* microseconds */
};
The function getitimer fills the structure indicated by value with the current set-
ting for the timer indicated by which (one of ITIMER_REAL, ITIMER_VIRTUAL, or
ITIMER_PROF). The element it_value is set to the amount of time remaining on the
timer, or zero if the timer is disabled. Similarly, it_interval is set to the
reset value. The function setitimer sets the indicated timer to the value in
value. If ovalue is nonzero, the old value of the timer is stored there.
Timers decrement from it_value to zero, generate a signal, and reset to it_inter-
val. A timer which is set to zero (it_value is zero or the timer expires and
it_interval is zero) stops.
Both tv_sec and tv_usec are significant in determining the duration of a timer.
Timers will never expire before the requested time, instead expiring some short,
constant time afterwards, dependent on the system timer resolution (currently
10ms). Upon expiration, a signal will be generated and the timer reset. If the
timer expires while the process is active (always true for ITIMER_VIRT) the signal
will be delivered immediately when generated. Otherwise the delivery will be off-
set by a small time dependent on the system loading.
RETURN VALUE
On success, zero is returned. On error, -1 is returned, and errno is set appropri-
ately.
ERRORS
EFAULT value or ovalue are not valid pointers.
EINVAL which is not one of ITIMER_REAL, ITIMER_VIRT, or ITIMER_PROF.
CONFORMING TO
SVr4, 4.4BSD (This call first appeared in 4.2BSD).
SEE ALSO
gettimeofday(2), sigaction(2), signal(2)
BUGS
Under Linux, the generation and delivery of a signal are distinct, and there each
signal is permitted only one outstanding event. It’s therefore conceivable that
under pathologically heavy loading, ITIMER_REAL will expire before the signal from
a previous expiration has been delivered. The second signal in such an event will
be lost.
Linux 0.99.11 1993-08-05 GETITIMER(2)
Generated by $Id: phpMan.php,v 4.55 2007/09/05 04:42:51 chedong Exp $ Author: Che Dong
On Apache/1.3.41 (Unix) PHP/5.2.5 mod_perl/1.30 mod_gzip/1.3.26.1a
Under GNU General Public License
2009-01-10 11:15 @38.103.63.58 CrawledBy CCBot/1.0 (+http://www.commoncrawl.org/bot.html)