getitimer man page on FreeBSD

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

     getitimer, setitimer — get/set value of interval timer

     Standard C Library (libc, -lc)

     #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() 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 expira‐
     tion.  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 dis‐
     ables 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 inter‐
     preted programs.  Each time the ITIMER_PROF timer expires, the SIGPROF
     signal is delivered.  Because this signal may interrupt in-progress sys‐
     tem calls, programs using this timer must be prepared to restart inter‐
     rupted system calls.

     The maximum number of seconds allowed for it_interval and it_value in
     setitimer() is 100000000.

     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.

     Upon successful completion, the value 0 is returned; otherwise the
     value -1 is returned and the global variable errno is set to indicate the

     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.

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

     The getitimer() system call appeared in 4.2BSD.

BSD				 May 16, 1995				   BSD

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