SYNOPSIS
        void heart_beat()

DESCRIPTION
        This function will be called automatically every
        __HEART_BEAT_INTERVAL__ seconds. The driver will call the function
        directly in the object, even if the function is being shadowed.

        The start and stop of heart beat is controlled by the efun
        set_heart_beat(). Be careful not to have objects with heart
        beat running all the time, as it uses a lot of driver
        resources. If there is an error in the heart beat routine, the
        heart beat will be turned off for this object and the
        master function heart_beat_error() is called. If the call
        to the master function returns a non-zero value, the heart beat
        will be turned back on again.

        The function this_player() will return this object, but only if
        it is living. Otherwise, this_player() will return 0.

        The function will be called only if there is at least one interactive
        user in the game.

        Note that error messages will be given to the current user
        which will be the object itself or nobody.

EXAMPLE
        object owner;
        void create() {
           ...
           owner=this_player();
           set_heart_beat(1);
        }
        void heart_beat() {
           tell_object(owner, "Your heart goes: BUM BUM\n");
        }

        We have to use tell_object() because write goes to the current
        user and this can only be the object itself or nobody.

HISTORY
        LDMud 3.3.687 made the interval time configurable at driver compile
        time (used to be 2 seconds fixed).

SEE ALSO
        set_heart_beat(E), call_out(E), enable_commands(E),
        heart_beat_error(M)