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GETITIMER(2) BSD System Calls Manual GETITIMER(2)
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);
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-nil).
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 dis-
abled 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 resolu-
tion (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 pro-
filing 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 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
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.
SEE ALSO
select(2), sigaction(2), gettimeofday(2)
HISTORY
The getitimer() function call appeared in 4.2BSD.
4.2 Berkeley Distribution December 11, 1993 4.2 Berkeley Distribution |
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