@Override
    public void start() {
        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 acquire
required resources for the processing element.
This will be called after initializing the system and before
starting to process the events.
modules/siddhi-core/src/main/java/io/siddhi/core/trigger/StartTrigger.java