Question

我使用Java中的Monitor（Synchronized）实现了Dining Philosopher问题。

该计划的目标是：

每个哲学家都应该遵循思考，筷子，吃饭，放筷子（没有竞争条件）的工作流程。
没有死锁

我认为这段代码似乎运行正常，但有些东西是不对的，因为它是永远运行的我试图调试它，调试工具停在这一行哲学家[i] .t.join（）;但该计划没有终止。

请帮助我确定问题或告诉我如何解决问题。谢谢你的建议。

MyMonitor类：

class MyMonitor {
    private enum States {THINKING, HUNGRY, EATING};
    private States[] state;

    public MyMonitor() {
        state = new States[5];
        for(int i = 0; i < 5; i++) {
            state[i] = States.THINKING;
            System.out.println("Philosopher " + i + " is THINKING");
        }
    }

    private void test(int i) {
        if((state[(i+4)%5]!=States.EATING) && (state[i]==States.HUNGRY) && (state[(i+1)%5]!=States.EATING)) {
            state[i] = States.EATING;
            System.out.println("Philosopher " + i + " is EATING");
            notify();
        }
    }

    public synchronized void pickup(int i) {
            state[i] = States.HUNGRY;
            System.out.println("Philosopher " + i + " is HUNGRY");      
            test(i);
            if (state[i] != States.EATING) {
                System.out.println("Philosopher " + i + " is WAITING");
                try {
                    wait();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
    }

    public synchronized void putdown(int i) {
            state[i] = States.THINKING;
            System.out.println("Philosopher " + i + " is THINKING");
            test((i+4)%5);
            test((i+1)%5);
        }
    }

MyPhilosopher类：

class MyPhilosopher implements Runnable{
    private int myID;
    private int eatNum;
    private MyMonitor monitor;
    private Thread t;

    public MyPhilosopher(int myID, int eatNum, MyMonitor monitor) {
        this.myID = myID;
        this.eatNum = eatNum;
        this.monitor = monitor;
        t = new Thread(this);
        t.start();
    }

    public void run() {
        int count = 1;
        while(count <= eatNum ){
            monitor.pickup(myID);
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            monitor.putdown(myID);
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            count++;
        }
    }

    public static void main(String[] args) {
        int eatNum = 10;

            System.out.println("----------------------------------------------------------------------------------------------------");
        System.out.println("xxx");
        System.out.println("xxx");
        System.out.println("xxx");
            System.out.println("----------------------------------------------------------------------------------------------------");
        System.out.println("Starting");
        System.out.println("----------------------------------------------------------------------------------------------------");
        System.out.println("");
        MyMonitor monitor = new MyMonitor();
        MyPhilosopher[] philosopher = new MyPhilosopher[5];

        for(int i = 0; i < 5; i++) {
            philosopher[i] = new MyPhilosopher(i, eatNum, monitor);
        }


        for(int i = 0; i < 5; i++) {
            try {
                philosopher[i].t.join();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }

            System.out.println("----------------------------------------------------------------------------------------------------");
        System.out.println("Ended");
    }
}

Answer 1

我已经执行了你的代码，它运行完美，直到两次或多次执行。此外，你可以减少睡眠时间，你的代码是正确但完美的，直到4个哲学家等待，其中一个正在吃。我不喜欢它。你正在打破一个coffman条件，但我建议你使用其他实现，如打破保持和等待条件。我的意思是，你既可以拿筷子也可以不拿筷子，其他的实施也可以，即使是哲学家拿筷子在右边，奇怪的哲学家拿左边的筷子。祝你好运！

Philosopher 4 is THINKING
Philosopher 0 is EATING
Philosopher 3 is HUNGRY
Philosopher 3 is WAITING
Philosopher 1 is HUNGRY
Philosopher 1 is WAITING
Philosopher 2 is THINKING
Philosopher 3 is EATING
Philosopher 0 is THINKING
Philosopher 1 is EATING
Philosopher 4 is HUNGRY
Philosopher 4 is WAITING
Philosopher 3 is THINKING
Philosopher 4 is EATING
Philosopher 2 is HUNGRY
Philosopher 2 is WAITING
Philosopher 0 is HUNGRY
Philosopher 0 is WAITING
Philosopher 1 is THINKING
Philosopher 2 is EATING
Philosopher 4 is THINKING
Philosopher 0 is EATING
Philosopher 3 is HUNGRY
Philosopher 3 is WAITING
Philosopher 2 is THINKING
Philosopher 3 is EATING
Philosopher 1 is HUNGRY
Philosopher 1 is WAITING
Philosopher 0 is THINKING
Philosopher 1 is EATING
Philosopher 4 is HUNGRY
Philosopher 4 is WAITING
Philosopher 3 is THINKING
Philosopher 4 is EATING
Philosopher 2 is HUNGRY
Philosopher 2 is WAITING
Philosopher 0 is HUNGRY
Philosopher 0 is WAITING
Philosopher 1 is THINKING
Philosopher 2 is EATING
Philosopher 3 is HUNGRY
Philosopher 3 is WAITING
Philosopher 4 is THINKING
Philosopher 0 is EATING
Philosopher 2 is THINKING
Philosopher 3 is EATING
Philosopher 1 is HUNGRY
Philosopher 1 is WAITING
Philosopher 4 is HUNGRY
Philosopher 4 is WAITING
Philosopher 0 is THINKING
Philosopher 1 is EATING
Philosopher 2 is HUNGRY
Philosopher 2 is WAITING
Philosopher 3 is THINKING
Philosopher 4 is EATING
Philosopher 1 is THINKING
Philosopher 2 is EATING
Philosopher 0 is HUNGRY
Philosopher 0 is WAITING
Philosopher 4 is THINKING
Philosopher 0 is EATING
Philosopher 3 is HUNGRY
Philosopher 3 is WAITING
Philosopher 2 is THINKING
Philosopher 3 is EATING
Philosopher 1 is HUNGRY
Philosopher 1 is WAITING
Philosopher 4 is HUNGRY
Philosopher 4 is WAITING
Philosopher 0 is THINKING
Philosopher 1 is EATING
Philosopher 2 is HUNGRY
Philosopher 2 is WAITING
Philosopher 3 is THINKING
Philosopher 4 is EATING
Philosopher 0 is HUNGRY
Philosopher 0 is WAITING
Philosopher 1 is THINKING
Philosopher 2 is EATING
Philosopher 4 is THINKING
Philosopher 0 is EATING
Philosopher 2 is THINKING
Philosopher 1 is HUNGRY
Philosopher 1 is WAITING
Philosopher 0 is THINKING
Philosopher 1 is EATING
Philosopher 1 is THINKING
----------------------------------------------------------------------------------------------------
Ended

但是，我已经检查过你在某些特殊情况下遇到了死锁：当所有哲学家中至少有人可以吃，而其他人则在等待。但是我已经通过在函数的头部中使用synchronize来改变你的代码，在while和在方法putdown（）中使用test（）方法的if条件我已经通过notifyAll（）更改了通知; 代码是这样的：

class MyMonitor {
private enum States {THINKING, HUNGRY, EATING};
private  States[] state;

public MyMonitor() {
    state = new States[5];
    for(int i = 0; i < 5; i++) {
        state[i] = States.THINKING;
        System.out.println("Philosopher " + i + " is THINKING");
    }
}

private synchronized void test(int i) {
    while((state[(i+4)%5]!=States.EATING) && (state[i]==States.HUNGRY) && (state[(i+1)%5]!=States.EATING)) {
        state[i] = States.EATING;
        System.out.println("Philosopher " + i + " is EATING");
     //   notify();
    }
}

public synchronized void pickup(int i) {
        state[i] = States.HUNGRY;
        System.out.println("Philosopher " + i + " is HUNGRY");      
        test(i);
        if (state[i] != States.EATING) {
            System.out.println("Philosopher " + i + " is WAITING");
            try {
                wait();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
}

public synchronized void putdown(int i) {
        state[i] = States.THINKING;
        System.out.println("Philosopher " + i + " is THINKING");
        //test((i+4)%5);
        //test((i+1)%5);
        notifyAll();
    }
}

我建议你使用一个或多个实现，然后再考虑你想要破解什么样的coffman条件。祝你好运

Thread.join（）在Dining Philosophers实现中没有达到预期效果

1 个答案: