Prog3A/praktkum3/DiningPhilosophers.java

import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

public class DiningPhilosophers {

    // Anzahl der Philosophen
    private static final int NUM_PHILOSOPHERS = 5;

    public static void main(String[] args) {
        Philosopher[] philosophers = new Philosopher[NUM_PHILOSOPHERS];
        Fork[] forks = new Fork[NUM_PHILOSOPHERS];

        // Initialisiere Gabeln
        for (int i = 0; i < NUM_PHILOSOPHERS; i++) {
            forks[i] = new Fork(i);
        }

        // Initialisiere Philosophen
        for (int i = 0; i < NUM_PHILOSOPHERS; i++) {
            Fork leftFork = forks[i];
            Fork rightFork = forks[(i + 1) % NUM_PHILOSOPHERS];

            // Um Deadlock zu vermeiden, greift der letzte Philosoph zuerst zur rechten Gabel.
            if (i == NUM_PHILOSOPHERS - 1) {
                philosophers[i] = new Philosopher(i, rightFork, leftFork);
            } else {
                philosophers[i] = new Philosopher(i, leftFork, rightFork);
            }

            new Thread(philosophers[i], "Philosopher-" + i).start();
        }
    }
}

class Fork {

    private final int id;
    private boolean inUse;

    // Konstruktor
    public Fork(int id) {
        this.id = id;
        this.inUse = false;
    }

    // Liefert die ID der Gabel zurück
    public int getId() {
        return id;
    }

    // Gabel aufnehmen
    public synchronized boolean take() {
        if (!inUse) {
            inUse = true; // Gabel ist jetzt in Benutzung
            try {
                Thread.sleep(1000); // 1 Sekunde warten, um die Gabel aufzunehmen
            } catch (InterruptedException e) {
                Thread.currentThread().interrupt();
            }
            return true;
        }
        return false; // Gabel ist bereits in Benutzung
    }

    // Gabel freigeben
    public synchronized void put() {
        inUse = false; // Gabel freigeben
    }

    @Override
    public String toString() {
        return "Fork-" + id;
    }
}


class Philosopher implements Runnable {
    private final int id;
    private final Fork leftFork;
    private final Fork rightFork;

    public Philosopher(int id, Fork leftFork, Fork rightFork) {
        this.id = id;
        this.leftFork = leftFork;
        this.rightFork = rightFork;
    }

    @Override
    public void run() {
        try {

            // Linke Gabel aufnehmen
            System.out.println("Philosopher-" + id + " is trying to get " + leftFork);
            while (!leftFork.take()) {
                Thread.yield(); // Busy waiting entschärfen
            }
            System.out.println("Philosopher-" + id + " got " + leftFork);

            // Rechte Gabel aufnehmen
            System.out.println("Philosopher-" + id + " is trying to get " + rightFork);
            while (!rightFork.take()) {
                Thread.yield(); // Busy waiting entschärfen
            }
            System.out.println("Philosopher-" + id + " got " + rightFork);

            // Philosoph isst
            System.out.println("Philosopher-" + id + " is eating.");
            Thread.sleep(2000); // 2 Sekunden essen

            // Gabeln freigeben
            leftFork.put();
            System.out.println("Philosopher-" + id + " put down " + leftFork);
            rightFork.put();
            System.out.println("Philosopher-" + id + " put down " + rightFork);

            // Philosoph beendet das Essen
            System.out.println("Philosopher-" + id + " finished eating.");
        } catch (InterruptedException e) {
            Thread.currentThread().interrupt();
            System.out.println("Philosopher-" + id + " was interrupted.");
        }
    }
}