wait()/ notify()无法正常工作

时间:2016-07-24 12:45:59

标签: java multithreading deadlock wait notify

我有一个ConsumerProducer对象,我想从两个不同的线程获取锁定。课程如下:

public class ConsumerProducer {

    public String stringPool = null;

    public void put(String s){
        stringPool = s;
    }

    public String get(){
        String ret = stringPool;
        stringPool = null;
        return ret;
    }

}

线程impl类如下:

public class WaitNotifyTest implements Runnable {

    private String threadType;
    public ConsumerProducer cp;
    public static volatile int i = 1;

    public WaitNotifyTest(String threadType, ConsumerProducer cp) {
        this.threadType = threadType;
        this.cp = cp;
    }

    public static void main(String[] args) throws InterruptedException {

        ConsumerProducer cp = new ConsumerProducer();
        WaitNotifyTest test1 = new WaitNotifyTest("Consumer", cp);
        WaitNotifyTest test2 = new WaitNotifyTest("Producer", cp);

        Thread t1 = new Thread(test1);
        Thread t2 = new Thread(test2);

        t1.start();
        t2.start();
        t1.join();
        t2.join();
    }

    @Override
    public void run() {
        while (true) {

            if (threadType.equalsIgnoreCase("Consumer")) {
                synchronized (cp) {
                    try {
                        if (null != cp.get()) {
                            cp.wait();
                        }
                        consume();
                        System.out.println("notify from Consumer");
                        cp.notify();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }

            } else {
                synchronized (cp) {
                    try {
                        if (null == cp.get()) {
                            cp.wait();
                        }
                        produce();
                        System.out.println("notify from Producer");
                        cp.notify();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            }
            if (i == 5) {
                break;
            }
            i++;
        }
    }

    public void consume() {
        System.out.println("Putting: Counter" + i);
        cp.put("Counter" + i);
    }

    public void produce() {
        System.out.println("getting: " + cp.get());
    }

}

但是当我运行代码时,它正面临某种死锁,并且像

一样被卡住了
Putting: Counter3
notify from Consumer

有些事情发生了严重错误,但我无法确定。请帮忙。

2 个答案:

答案 0 :(得分:1)

您的消费者正在做生产者的工作,生产者正在做消费者的工作。 交换责任并修改条件等。请参考下面的代码。

  1. 当没有任何东西可以获取时,消费者会等待,他会释放cp的锁定。这样生产者就有机会进入同步区块。
  2. 制片人只在没有任何东西时生产,否则他会等待。之后,他将释放cp的锁定。这样消费者就有机会进入同步区块。
  3. 消费者就是把事情赶走的人。
  4. 制作人将事情放在桌面上。
  5. 根据你的评论。你想把Counter从1改为5,所以你应该只在Producer线程中添加i ++。如何控制两个线程的增加?
  6. 您无法判断消费者或制作人是否从get()对象调用cp,而是将{null}分配给stringPool。这显然是错误的,并且会使消费者从公共空间中获得空位。我添加了一个新方法clearString(),只有当消费者对产品进行了补充时,才会将公共空间设置为null。

    public class WaitNotifyTest implements Runnable {
    
    private String threadType;
    public ConsumerProducer cp;
    public static volatile int i = 0;
    
    public WaitNotifyTest(String threadType, ConsumerProducer cp) {
        this.threadType = threadType;
        this.cp = cp;
    }
    
    public static void main(String[] args) throws InterruptedException {
    
        ConsumerProducer cp = new ConsumerProducer();
        WaitNotifyTest test1 = new WaitNotifyTest("Consumer", cp);
        WaitNotifyTest test2 = new WaitNotifyTest("Producer", cp);
    
        Thread t1 = new Thread(test1);
        Thread t2 = new Thread(test2);
    
        t1.start();
        t2.start();
        t1.join();
        t2.join();
    }
    
    @Override
    public void run() {
        while (true) {
            if (threadType.equalsIgnoreCase("Consumer")) {
                synchronized (cp) {
                    try {
                        /*
                         * Consumer will wait when there is nothing to get and he will release the lock of cp.
                         * So that producer has change to go into the synchronized block.
                         */
    
                        if (null == cp.get()) {
                            cp.wait();
                        }
                        consume();
                        System.out.println("notify from Consumer");
                        cp.notify();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
    
            } else {
                synchronized (cp) {
                    try {
                        /*
                         * Producer only produce when there is nothing or he will wait. At the same time, he will release the lock of cp.
                         * So that consumer has chance to go into the synchronized block.
                         */
                        if (null != cp.get()) {
                            cp.wait();
                        }
                        i++;
                        produce();
                        System.out.println("notify from Producer");
                        cp.notify();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            }
            if (i == 5) {
                break;
            }
    
        }
    }
    
    public void consume() {
        System.out.println("getting: " + cp.get());
        cp.clearString();
    }
    
    public void produce() {
        System.out.println("Putting: Counter" + i);
        cp.put("Counter" + i);
    }}
    
  7. 另请参阅ConsumerProducer类。

    public class ConsumerProducer {
            public String stringPool = null;
    
            public void put(String s){
                stringPool = s;
            }
    
            public String get(){
                return stringPool;
            }
    
            public void clearString(){
                stringPool = null;
            }
    }
    

答案 1 :(得分:0)

更新的代码在这里: ConsumerProducer.java:
    公共类ConsumerProducer {

    public volatile String stringPool = null;

    public void put(String s){
        this.stringPool = s;
    }

    public String get(){
        String ret = this.stringPool;
        //this.stringPool = null;
        return ret;
    }
    //added
    public void clearString(){
        this.stringPool = null;
    }

}

WaitNotifyTest.java     公共类WaitNotifyTest实现Runnable {

    private String threadType;
    public ConsumerProducer cp;
    public static volatile int i = 0;

    public WaitNotifyTest(String threadType, ConsumerProducer cp) {
        this.threadType = threadType;
        this.cp = cp;
    }

    public static void main(String[] args) throws InterruptedException {

        ConsumerProducer cp = new ConsumerProducer();
        WaitNotifyTest test1 = new WaitNotifyTest("Consumer", cp);
        WaitNotifyTest test2 = new WaitNotifyTest("Producer", cp);

        Thread t1 = new Thread(test1);
        Thread t2 = new Thread(test2);

        t1.start();
        t2.start();
        t1.join();
        t2.join();
    }

    @Override
    public void run() {
        while (true) {

            if (threadType.equalsIgnoreCase("Consumer")) {
                synchronized (cp) {
                    try {
                        if (null == cp.get()) {
                            cp.wait();
                        }
                        consume();
                        System.out.println("notify from Consumer");
                        cp.notify();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }

            } else {
                synchronized (cp) {
                    try {
                        if (null != cp.get()) {
                            cp.wait();
                        }
                        i++;
                        produce();
                        System.out.println("notify from Producer");
                        cp.notify();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            }
            if (i == 5) {
                break;
            }

        }
    }

    public void produce() {
        System.out.println("Putting: Counter" + i);
        cp.put("Counter" + i);
    }

    public void consume() {
        System.out.println("getting: " + cp.get());
        cp.clearString();
    }

}