SyncPhilosopher.java

public class SyncPhilosopher implements Runnable {

    private Object left;
    private Object right;
    private int num;
    

    public SyncPhilosopher(int num, Object left, Object right) {
        this.left = left;
        this.right = right;
        this.num = num;
    }

    public synchronized void test() {
        // irgendwas nebenlaeufiges
    }

    // ist das gleiche wie
    // public void test() {
    //    // sehr ressourcenlastige Berechnung
    //     synchronized(this) {
    //        irgendwas nebenlaeufiges
    //     }
    // }
    
    public void run() {
        // sehr naive Loesung
        while (true) {
            // thinking
            System.out.println(num + " thinking");
            // eating
            synchronized(left) {
                synchronized(right) {
                    try {
                        Thread.sleep((long) 1000*Math.random());
                    } catch (InterruptedException e) {
                    }
                  System.out.println(num + " eating");
                } // Lock "right" wieder frei
            } // Lock "left" wieder frei
        }
    }

    public static void main(String[] args) {
        int count = 4;

        if (args.length > 0) {
            try {
                count = Integer.parseInt(args[0]);
            } catch (NumberFormatException e) {
            }
        }

        Object sticks[] = new Object[count];
        SyncPhilosopher phils[] = new SyncPhilosopher[count];

        // 
        for (int i=0; i<count; i++) {
            sticks[i] = new Object(); 
        }

        for (int i=0; i<count-1; i++) {
            phils[i] = new SyncPhilosopher(i,sticks[i],sticks[(i+1) % count]);
            new Thread(phils[i]).start();
            // bei `extends Thread`:
            // phils[i].start()
        }

        phils[3] = new SyncPhilosopher(3,sticks[0],sticks[3]);
        new Thread(phils[3]).start();
        
    }

}