GETITIMER(2) BSD System Calls Manual GETITIMER(2)NAME
getitimer, setitimer — get/set value of interval timer
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <sys/time.h>
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 not NULL.
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 expira‐
tion. 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 dis‐
ables a timer. Setting it_interval to 0 causes a timer to be disabled
after its next expiration (assuming it_value is non-zero).
The which parameter specifies the type of the timer:
ITIMER_REAL timer decrements in real time. This timer is
affected by adjtime(2) and settimeofday(2). A
SIGALRM signal is delivered when this timer
expires.
ITIMER_VIRTUAL timer decrements in process virtual time. It
runs only when the process is executing. A
SIGVTALRM signal is delivered when it expires.
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 inter‐
preters 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.
ITIMER_MONOTONIC timer decrements in monotonic time. This timer
is not affected by adjtime(2) and
settimeofday(2). A SIGALRM signal is delivered
when this timer expires.
Note that:
· Time values smaller than the resolution of the system clock are
rounded up to this resolution (typically 10 milliseconds).
· The interaction between setitimer() and alarm(3) or sleep(3) is
unspecified by the specification.
RETURN VALUES
If the calls succeed, a value of 0 is returned. If an error occurs, the
value -1 is returned, and a more precise error code is placed in the
global variable errno.
ERRORS
Both functions may fail if:
[EFAULT] The value parameter specified a bad address.
[EINVAL] The which parameter was not a known timer type, or the
value parameter specified a time that was too large to
be handled.
SEE ALSOgettimeofday(2), select(2), sigaction(2), itimerval(3), timeradd(3)STANDARDS
The functions conform to IEEE Std 1003.1-2001 (“POSIX.1”). The later
IEEE Std 1003.1-2008 (“POSIX.1”) revision however marked both as obsoles‐
cent, recommending the use of timer_gettime(2) and timer_settime(2)
instead.
HISTORY
The getitimer() function call appeared in 4.2BSD. The ITIMER_MONOTONIC
functionality appeared in NetBSD 6.0.
BSD October 27, 2011 BSD