@Override
    public void stop() {
        try {
            if (scheduler != null) {
                scheduler.deleteJob(new JobKey(jobName, jobGroup));
                if (log.isDebugEnabled()) {
                    log.debug("Scheduler job: " + jobName + " Group: " + jobGroup + " has successfully stopped");
                }
            }
        } catch (SchedulerException e) {
            log.error(ExceptionUtil.getMessageWithContext(e, siddhiAppContext) +
                    " Error while removing the cron trigger job '" + jobGroup + "':'" + jobName + "'", 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