setitimer



GETITIMER(2)              OpenBSD Programmer's 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);

     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

     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]           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

     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.

OpenBSD 5.4                      July 17, 2013                     OpenBSD 5.4

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