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OpenDarwin 7.2.1 - man page for setitimer (opendarwin section 2)

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GETITIMER(2)			     BSD System Calls Manual			     GETITIMER(2)

     getitimer, setitimer -- get/set value of interval timer

     #include <sys/time.h>
     #define ITIMER_REAL      0
     #define ITIMER_VIRTUAL   1
     #define ITIMER_PROF      2

     getitimer(int which, struct itimerval *value);

     setitimer(int which, const struct itimerval *value, struct itimerval *ovalue);

     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.

     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).

     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.

     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.

     select(2), sigaction(2), gettimeofday(2)

     The getitimer() function call appeared in 4.2BSD.

4.2 Berkeley Distribution		December 11, 1993		4.2 Berkeley Distribution
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