noble (2) getitimer.2freebsd.gz

NAME

     getitimer, setitimer — get/set value of interval timer

LIBRARY

     Standard C Library (libc, -lc)

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()
     system call returns the current value for the timer specified in which in the structure at value.  The
     setitimer() system call sets a timer to the specified value (returning the previous value of the timer if
     ovalue is not a null pointer).

     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, regardless of the value of it_interval.  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 maximum number of seconds allowed for it_interval and it_value in setitimer() is 100000000.

NOTES

     Three macros for manipulating time values are defined in <sys/time.h>.  The timerclear() macro sets a time
     value to zero, timerisset() tests if a time value is non-zero, and timercmp() compares two time values.

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

     The getitimer() and setitimer() system calls will fail if:

     [EFAULT]           The value argument specified a bad address.

     [EINVAL]           The value argument specified a time that was too large to be handled.

SEE ALSO

     gettimeofday(2), select(2), sigaction(2), clocks(7)

STANDARDS

     The getitimer() and setitimer() functions conform to IEEE Std 1003.1-2001 (“POSIX.1”).  The later IEEE Std
     1003.1-2008 (“POSIX.1”) revision however marked both functions as obsolescent, recommending the use of
     timer_gettime(2) and timer_settime(2) instead.

HISTORY

     The getitimer() system call appeared in 4.2BSD.