NAME
getitimer,
setitimer —
get/set value of interval
timer
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);
void
timerclear(struct
timeval *);
int
timerisset(struct
timeval *);
int
timercmp(struct
timeval *a, struct
timeval *b,
CMP);
void
timersub(struct
timeval *a, struct
timeval *b, struct
timeval *res);
void
timeradd(struct
timeval *a, struct
timeval *b, struct
timeval *res);
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
non-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 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. Setting it_interval to 0 causes a timer to be disabled after its next expiration (assuming it_value is non-zero).
Time values smaller than the resolution of the system clock are rounded up to this resolution (typically 10 milliseconds).
The 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 remaining five functions are in fact macros for manipulating
time values, defined in
<sys/time.h>.
timerclear(a)
sets the time value in a to zero.
timerisset(a)
tests if the time value in a is non-zero.
timercmp(a,
b, CMP) compares two time values
in the form a CMP b, where
CMP is <, <=, ==, !=, >=, or > .
timersub(a,
b, res) subtracts
a - b and stores the result in
res.
timeradd(a,
b, res) adds two timers and
stores the result in res.
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
getitimer() and
setitimer() will fail if:
- [
EFAULT] - The value parameter specified a bad address.
- [
EINVAL] - An unrecognized value for which was specified.
In addition, setitimer() may return the
following error:
- [
EINVAL] - value or ovalue specified a time that was too large to be handled.
SEE ALSO
clock_gettime(2), gettimeofday(2), poll(2), select(2), sigaction(2)
STANDARDS
The getitimer() and
setitimer() functions conform to
IEEE Std 1003.1-2008 (“POSIX.1”).
HISTORY
The getitimer() and
setitimer() system calls first appeared in
4.1cBSD.