MirOS Manual: getitimer(2), setitimer(2), timeradd(3), timerclear(3), timercmp(3), timerisset(3), timersub(3)

GETITIMER(2)               BSD Programmer's 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);

     timerclear(struct timeval *);

     timerisset(struct timeval *);

     timercmp(struct timeval *a, struct timeval *b, CMP);

     timersub(struct timeval *a, struct timeval *b, struct timeval *res);

     timeradd(struct timeval *a, struct timeval *b, struct timeval *res);


     The system provides each process with three interval timers, defined in
     <sys/time.h>. The getitimer() call returns the current value for the ti-
     mer 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-null).

     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 re-
     loading it_value when the timer expires. Setting it_value to 0 disables 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).

     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

     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

     The remaining five functions are in fact macros for manipulating time
     values, defined in <sys/time.h>.

     timerclear(a) sets the time value in a to zero.

     timerisset(a) tests if the time value in a is non-zero.

     timercmp(a, b, CMP) compares two time values in the form a CMP b, where
     CMP is <, <=, ==, !=, >=, or > .

     timersub(a, b, res) subtracts a - b and stores the result in res.

     timeradd(a, b, res) adds two timers and stores the result in res.


     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 glo-
     bal 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

     [EINVAL]      An unrecognized value for which was specified.


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


     The getitimer() function call appeared in 4.2BSD.

MirOS BSD #10-current         December 11, 1993                              1

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