关于线程死锁有关问题 wait notifyAll

public class ProducerConsumer{    public static void main(String[] args){        SyncStack ss = new SyncStack();        Producer p = new Producer(ss);        Producer pp = new Producer(ss);        Consumer c = new Consumer(ss);        new Thread(pp).start();        new Thread(p).start();        new Thread(c).start();    }}class WoTou{    int id;    WoTou(int id){        this.id=id;    }    public String toString(){        return "WoTou:"+id;    }}class SyncStack{    int index = 0;    WoTou[] arrwt=new WoTou[6];        public synchronized void push(WoTou wt){        while(index==arrwt.length){            try{                this.wait();            }catch(InterruptedException e){                System.out.println(e);            }        }        this.notifyAll();        arrwt[index]=wt;        index++;            }    public synchronized WoTou pop(){        while(index==0){            try{                this.wait();            }catch(InterruptedException e){                System.out.println(e);            }        }        this.notifyAll();        index--;        return arrwt[index];    }}class Producer implements Runnable{    SyncStack ss=null;    Producer(SyncStack ss){        this.ss=ss;    }    public void run(){        for(int i=0;i<10;i++){            WoTou wt = new WoTou(i);            ss.push(wt);            System.out.println("生产："+wt);            try {                Thread.sleep((int)(Math.random() * 200));            } catch (InterruptedException e) {                e.printStackTrace();            }        }    }}class Consumer implements Runnable{    SyncStack ss = null;    Consumer(SyncStack ss){        this.ss=ss;    }    public void run(){        for(int i=0;i<10;i++){            WoTou wt=ss.pop();            System.out.println("消费："+wt);            try {                Thread.sleep((int)(Math.random() * 200));            } catch (InterruptedException e) {                e.printStackTrace();            }        }    }}