GETITIMER(2)GETITIMER(2)NAME
getitimer, setitimer - get/set value of interval timer
SYNOPSIS
#include <sys/time.h>
#define ITIMER_REAL 0 /* real time intervals */
#define ITIMER_VIRTUAL 1 /* virtual time intervals */
#define ITIMER_PROF 2 /* user and system virtual time */
getitimer(which, value)
int which;
struct itimerval *value;
setitimer(which, value, ovalue)
int which;
struct itimerval *value, *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 nonzero).
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.
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.
NOTES
Three macros for manipulating time values are defined in <sys/time.h>.
Timerclear sets a time value to zero, timerisset tests if a time value
is non-zero, and timercmp compares two time values (beware that >= and
<= do not work with this macro).
RETURN VALUE
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
The possible errors are:
[EFAULT] The value parameter specified a bad address.
[EINVAL] A value parameter specified a time was too large to be
handled.
SEE ALSOsigvec(2), gettimeofday(2)4.2 Berkeley Distribution August 26, 1985 GETITIMER(2)
