NAME
getitimer, setitimer — get/set value of interval timerLIBRARY
Standard C Library (libc, -lc)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 *value, struct itimerval *ovalue);
DESCRIPTION
The system provides each process with three interval timers, defined in <sys/time.h>. The getitimer() system call returns the current value for the timer specified in which in the structure at value. The setitimer() system call sets a timer to the specified value (returning the previous value of the timer if ovalue is not a null pointer). A timer value is defined by the itimerval structure:
struct itimerval {
struct timeval it_interval; /* timer interval */
struct timeval it_value; /* current value */
};
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.
The maximum number of seconds allowed for
it_interval and
it_value in
setitimer() is 100000000.
NOTES
Three macros for manipulating time values are defined in <sys/time.h>. The timerclear() macro sets a time value to zero, timerisset() tests if a time value is non-zero, and timercmp() compares two time values.RETURN VALUES
Upon successful completion, the value 0 is returned; otherwise the value -1 is returned and the global variable errno is set to indicate the error.ERRORS
The getitimer() and setitimer() system calls will fail if:- [
EFAULT] - The value argument specified a bad address.
- [
EINVAL] - The value argument specified a time that was too large to be handled.
SEE ALSO
gettimeofday(2), select(2), sigaction(2), clocks(7)STANDARDS
The getitimer() and setitimer() functions conform to IEEE Std 1003.1-2001 (“POSIX.1”). The later IEEE Std 1003.1-2008 (“POSIX.1”) revision however marked both functions as obsolescent, recommending the use of timer_gettime(2) and timer_settime(2) instead.HISTORY
The getitimer() system call appeared in 4.2BSD.| May 1, 2020 | Debian |