opendarwin man page for setitimer

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 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.

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