setitimer man page on BSDi

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GETITIMER(2)		    BSD Programmer's Manual		  GETITIMER(2)

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

SYNOPSIS
     #include <time.h>

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

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

DESCRIPTION
     The system provides each process with three interval timers: ITIMER_REAL,
     ITIMER_VIRTUAL and ITIMER_PROF.

     The getitimer() call returns the current value for the timer specified in
     which in the structure at value.

     The setitimer() call sets the timer specified in which to the specified
     value, and returns the previous value of the timer if ovalue is not NULL.

     The which parameter is one of the following:

     ITIMER_REAL
	  This timer decrements in real time.  A SIGALRM signal is delivered
	  when this timer expires.

     ITIMER_VIRTUAL
	  This timer decrements in process virtual time.  It runs only when
	  the process is executing.  A SIGVTALRM signal is delivered when it
	  expires.

     ITIMER_PROF
	  This timer decrements both in process virtual time and when the sys-
	  tem 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.

     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.  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).

NOTES
     Three macros for manipulating time values are defined in <time.h>.
     Timerclear sets a time value to zero, timerisset tests if a time value is
     non-zero, and timercmp compares two time values.

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),	 sigvec(2),  gettimeofday(2)

HISTORY
     The getitimer function call appeared in 4.2BSD.

4.2 Berkeley Distribution	 May 16, 1995				     2
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