setitimer(2) [freebsd man page]

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

NAME

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

LIBRARY

     Standard C Library (libc, -lc)

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() 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 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, 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 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.

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

NOTES

     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.

RETURN 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
     error.

ERRORS

     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.

SEE ALSO

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

HISTORY

     The getitimer() system call appeared in 4.2BSD.

BSD
								   May 16, 1995 							       BSD

GETITIMER(2)							System Calls Manual						      GETITIMER(2)

NAME

       getitimer, setitimer - get/set value of interval timer

SYNOPSIS

       #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 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 nonzero).

       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 resolution (on the VAX, 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).

NOTES  (PDP-11)
       On the PDP-11, setitimer rounds timer values up to seconds resolution.  (This saves some space and computation in the  overburdened  PDP-11
       kernel.)

RETURN VALUE

       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

       The possible errors are:

       [EFAULT]       The value parameter specified a bad address.

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

SEE ALSO

       sigvec(2), gettimeofday(2)

4.2 Berkeley Distribution					  August 26, 1985						      GETITIMER(2)