Question

Maybe this question has been asked many times before, but I never found a satisfying answer.

The problem:

I have to simulate a process scheduler, using the round robin strategy. I’m using threads to simulate processes and multiprogramming; everything works fine with the JVM managing the threads. But the thing is that now I want to have control of all the threads so that I can run each thread alone by a certain quantum (or time), just like real OS processes schedulers.

What I’m thinking to do:

I want have a list of all threads, as I iterate the list I want to execute each thread for their corresponding quantum, but as soon the time’s up I want to pause that thread indefinitely until all threads in the list are executed and then when I reach the same thread again resume it and so on.

The question:

So is their a way, without using deprecated methods stop(), suspend(), or resume(), to have this control over threads?

Answer 1

Who said Java is not low level enough?

Here is my 3 minute solution. I hope it fits your needs.

import java.util.ArrayList;
import java.util.List;

public class ThreadScheduler {

    private List<RoundRobinProcess> threadList
            = new ArrayList<RoundRobinProcess>();

    public ThreadScheduler(){
        for (int i = 0 ; i < 100 ; i++){
            threadList.add(new RoundRobinProcess());
            new Thread(threadList.get(i)).start();
        }
    }


    private class RoundRobinProcess implements Runnable{

        private final Object lock = new Object();
        private volatile boolean suspend = false , stopped = false;

        @Override
        public void run() {
            while(!stopped){
                while (!suspend){
                    // do work
                }
                synchronized (lock){
                    try {
                        lock.wait();
                    } catch (InterruptedException e) {
                        Thread.currentThread().interrupt();
                        return;
                    }
                }
            }
        }

        public void suspend(){
            suspend = true;
        }
        public void stop(){
            suspend = true;stopped = true;
            synchronized (lock){
                lock.notifyAll();
            }
        }

        public void resume(){
            suspend = false;
            synchronized (lock){
                lock.notifyAll();
            }
        }

    }
}

Please note that “do work” should not be blocking.