code: public static void clearThreadPool() {
  		for (ExecutorService pool:threadPool) {
  			pool.shutdown();
  		}
  		
  		for (ExecutorService pool:threadPool) {
  			try {
  				pool.awaitTermination(10, TimeUnit.SECONDS);
  			} catch (InterruptedException e) {
  				e.printStackTrace();
  			}
  		}
  		
  		threadPool.clear();
  	}
docs: /*
  Stop