code: public static void destroy() {
  		try {
  			logger.info("--- Para.destroy() ---");
  			for (DestroyListener destroyListener : DESTROY_LISTENERS) {
  				if (destroyListener != null) {
  					destroyListener.onDestroy();
  					logger.debug("Executed {}.onDestroy().", destroyListener.getClass().getName());
  				}
  			}
  			if (!EXECUTOR.isShutdown()) {
  				EXECUTOR.shutdown();
  				EXECUTOR.awaitTermination(60, TimeUnit.SECONDS);
  			}
  			if (!SCHEDULER.isShutdown()) {
  				SCHEDULER.shutdown();
  				SCHEDULER.awaitTermination(60, TimeUnit.SECONDS);
  			}
  		} catch (Exception e) {
  			logger.error("Failed to destroy Para.", e);
  		}
  	}
docs: Calls all registered listeners on exit. Call this method last.