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filnavn: Stemmesystem.java
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import java.util.ArrayDeque;

public class Stemmesystem
{
    private ArrayDeque<Integer> stemmer;

    public Stemmesystem()
    {
        stemmer = new ArrayDeque<>();
    }

    public void leggTilStemme(int stemme)
    {
        stemmer.push(stemme);
    }

    public int hentStemme()
    {
        if (tom())
        {
            return -1;
        }
        else
        {
            return stemmer.pop();
        }
    }

    public boolean tom()
    {
        return stemmer.isEmpty();
    }
}

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filnavn: MonitorStemmesystem.java
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import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

public class MonitorStemmesystem
{
    private Stemmesystem stemmesystem;

    private Lock laas;
    private Condition kanHente;

    public MonitorStemmesystem(Stemmesystem stemmesystem)
    {
        this.stemmesystem = stemmesystem;

        laas = new ReentrantLock(true);
        kanHente = laas.newCondition();
    }

    public void leggTilStemme(int stemme)
    {
        laas.lock();

        try
        {
            stemmesystem.leggTilStemme(stemme);

            kanHente.signalAll();
        }
        finally
        {
            laas.unlock();
        }
    }

    public int hentStemme() throws InterruptedException
    {
        laas.lock();

        try
        {
            while (tom())
            {
                kanHente.await();
            }

            return stemmesystem.hentStemme();
        }
        finally
        {
            laas.unlock();
        }
    }

    public boolean tom()
    {
        laas.lock();

        try
        {
            return stemmesystem.tom();
        }
        finally
        {
            laas.unlock();
        }
    }
}

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filnavn: Stemmekontor.java
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import java.util.Random;
import java.util.concurrent.CountDownLatch;

public class Stemmekontor implements Runnable
{
    private String sted;
    private MonitorStemmesystem monitor;
    private CountDownLatch antallStemmeurner;

    private Random generator;
    
    public Stemmekontor(String sted, MonitorStemmesystem monitor, CountDownLatch antallStemmeurner)
    {
        this.sted = sted;
        this.monitor = monitor;
        this.antallStemmeurner = antallStemmeurner;

        generator = new Random();
    }

    @Override
    public void run()
    {
        int antallStemmerPerUrne = 100;
        
        while (antallStemmeurner.getCount() != 0)
        {
            for (int i = 0; i < antallStemmerPerUrne; i ++)
            {
                monitor.leggTilStemme(generator.nextInt(10)); // 0 <= stemme <= 9
            }

            System.out.println(sted + " la til stemmer.");
            antallStemmeurner.countDown();
        }
    }
}

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filnavn: Stemmeteller.java
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import java.util.concurrent.BrokenBarrierException;
import java.util.concurrent.CyclicBarrier;

public class Stemmeteller implements Runnable
{
    private int id;
    private MonitorStemmesystem monitor;
    private CyclicBarrier tidForPause;
    
    public Stemmeteller(int id, MonitorStemmesystem monitor, CyclicBarrier tidForPause)
    {
        this.id = id;
        this.monitor = monitor;
        this.tidForPause = tidForPause;
    }

    @Override
    public void run()
    {
        try
        {
            int antallTalt = 0;
            int skalTelle = 100;
    
            int stemme;
    
            while (antallTalt < skalTelle)
            {
                stemme = monitor.hentStemme();
                System.out.println(id + ": " + stemme);
    
                antallTalt ++;
            }
    
            System.out.println(id + " er klar for pause.");

            tidForPause.await();

            System.out.println(id + " tar en pause.");
        } 
        catch (InterruptedException e)
        {
            System.err.println("Traaden ble avbrutt.");
            return;
        } 
        catch (BrokenBarrierException e) 
        {
            System.err.println("Barrieren ble brutt.");
            return;
        }
    }
}

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filnavn: Hovedprogram.java
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import java.util.concurrent.CountDownLatch;
import java.util.concurrent.CyclicBarrier;

public class Hovedprogram
{
    public static void main(String[] args) throws InterruptedException
    {
        Stemmesystem stemmesystem = new Stemmesystem();

        MonitorStemmesystem monitor = new MonitorStemmesystem(stemmesystem);

        /* Klargjor stemmekontorene */

        int antallUrner = 10;

        CountDownLatch antallStemmeUrner = new CountDownLatch(antallUrner);

        Thread grunerlokka = new Thread(new Stemmekontor("Grunerlokka", monitor, antallStemmeUrner));
        Thread blindern = new Thread(new Stemmekontor("Blindern", monitor, antallStemmeUrner));

        /* Klargjor stemmetellerne */

        int antallStemmetellere = Runtime.getRuntime().availableProcessors(); // 8

        CyclicBarrier tidForPause = new CyclicBarrier(antallStemmetellere);

        Thread[] stemmetellere = new Thread[antallStemmetellere];

        for (int id = 0; id < antallStemmetellere; id ++)
        {
            stemmetellere[id] = new Thread(new Stemmeteller(id, monitor, tidForPause));
        }

        /* Setter stemmetellerne og stemmekontorene i gang */

        for (Thread stemmeteller : stemmetellere)
        {
            stemmeteller.start();
        }

        grunerlokka.start();
        blindern.start();

        antallStemmeUrner.await();

        System.out.println("Stemmeurnene er lagt til.");
    }
}