getitimer(2)							  getitimer(2)

Name
       getitimer, setitimer - get or set value of interval timer

Syntax
       #include <sys/time.h>

       #define ITIMER_REAL	0    /* real time intervals */
       #define ITIMER_VIRTUAL	1    /* virtual time intervals */
       #define ITIMER_PROF	2    /* user and system virtual time */

       getitimer(which, value)
       int which;
       struct itimerval *value;

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

Description
       The system provides each process with three interval timers, defined in
       <sys/time.h>.  The call returns the current value for the timer	speci‐
       fied  in	 which,	 while the call sets the value of a timer (optionally,
       returning the previous value of the timer).  The upper limit  for  time
       values are as follows:

	  For VAX machines, 10millisec * 0x7fffffff  (about 256 days)
	  For RISC machines, 3.906 millsec * 0x7fffffff (about 97 days)

       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 nonzero, it indicates the time to the next timer expira‐
       tion.  If it_interval is nonzero, it specifies a value to  be  used  in
       reloading  it_value when the timer expires.  Setting it_value to 0 dis‐
       ables a timer.  Setting it_interval to 0 causes a timer to be  disabled
       after its next expiration (assuming it_value is nonzero).

       Time values smaller than the resolution of the system clock are rounded
       up to this resolution (on MIPS, 3.906 milliseconds;  on	VAX,  10  mil‐
       liseconds).

       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
       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>.
       The  timerclear	sets  a time value to zero, timerisset tests if a time
       value is nonzero, 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.

Diagnostics
       The possible errors are:

       [EFAULT]	      The value structure specified a bad address.

       [EINVAL]	      A value structure specified a time that was too large to
		      be handled.

See Also
       gettimeofday(2), sigvec(2), pause(3)

								  getitimer(2)

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