import java.util.Scanner;
import java.util.Random;

public class CheckpointSync{
	public static void main(String[] args){
		System.out.print("Enter number of workers to use: ");
		Scanner in = new Scanner(System.in);
		Worker.nWorkers = in.nextInt();
		System.out.print("Enter number of tasks to complete:");
		runTasks(in.nextInt());
	}

	
	private static void runTasks(int nTasks){
		for(int i = 0; i < nTasks; i++){
			System.out.println("Starting task number " + (i+1) + ".");
			runThreads();
			Worker.checkpoint();
		}
	}

	
	private static void runThreads(){
		for(int i = 0; i < Worker.nWorkers; i ++){
			new Thread(new Worker(i+1)).start();
		}
	}

	
	public static class Worker implements Runnable{
		public Worker(int threadID){
			this.threadID = threadID;
		}
		public void run(){
			work();
		}

		
		private synchronized void work(){
			try {
				int workTime = rgen.nextInt(900) + 100;
				System.out.println("Worker " + threadID + " will work for " + workTime + " msec.");
				Thread.sleep(workTime);