private void sendEvent() {
        long currentTime = siddhiAppContext.getTimestampGenerator().currentTime();
        if (throughputTracker != null && Level.BASIC.compareTo(siddhiAppContext.getRootMetricsLevel()) <= 0) {
            throughputTracker.eventIn();
        }
        Event event = new Event(currentTime, new Object[]{currentTime});
        try {
            streamJunction.sendEvent(event);
        } catch (Exception e) {
            streamJunction.handleError(event, e);
        }
    }
This will be called only once and this can be used to release
the acquired resources for processing.
This will be called before shutting down the system.
modules/siddhi-core/src/main/java/io/siddhi/core/trigger/CronTrigger.java