The setitimer function sets the timer specified by which to the
    value specified by 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;
                   struct  timeval it_value;
           };

    The value of the itimerval structure members are: as follows

    itimerval Member
    Value              Meaning

    it_interval = 0    Disables a timer after its next expiration
                       (assumes it_value is nonzero).
    it_interval =      Specifies a value used in reloading it_value
    nonzero            when the timer expires.
    it_value = 0       Disables a timer.
    it_value =         Indicates the time to the next timer
    nonzero            expiration.

    Time values smaller than the resolution of the system clock are
    rounded up to this resolution.

    The getitimer function provides one interval timer, defined in
    the <time.h> header file as ITIMER_REAL. This timer decrements in
    real time. When the timer expires, it delivers a SIGALARM signal.

                                   NOTE

       The interaction between setitimer and any of alarm, sleep,
       or usleep is unspecified.