getitimer, setitimer - get/set value of interval timer
#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);
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 inprogress 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.
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.
getitimer() and setitimer() will fail if:
[EFAULT] The value parameter specified a bad address.
[EINVAL] A value parameter specified a time that was
too large to be
handled.
gettimeofday(2), poll(2), select(2), sigaction(2)
The getitimer() function call appeared in 4.2BSD.
OpenBSD 3.6 December 11, 1993
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