java生产者/消费者模式实现——一生产者一消费者（操作值）

Posted 2020-06-17

 胶多不粘话多不甜，直接上代码：

生产者类：

/**
 * Created by 51304 on 2016/2/28.
 */
public class P {
    private String lock;
    public P(String lock){
        this.lock = lock;
    }

    public void setValue(){
        try{
            synchronized (this.lock){
                if(!ValueObject.value.equals("")){
                    lock.wait();
                }
                String value = System.currentTimeMillis() + "_" +
                        System.nanoTime();
                System.out.println("set value is " + value);
                ValueObject.value = value;
                lock.notify();
            }
        } catch (InterruptedException e){
            e.printStackTrace();
        }
    }
}

消费者类：

import com.sun.org.apache.xpath.internal.SourceTree;

/**
 * Created by 51304 on 2016/2/28.
 */
public class C {
    private String lock;
    public C(String lock){
        this.lock = lock;
    }

    public void getValue(){
        try{
            synchronized (this.lock){
                if(ValueObject.value.equals("")){
                    this.lock.wait();
                }
                System.out.println("get value is " + ValueObject.value);
                ValueObject.value = "";
                this.lock.notify();
            }
        } catch (InterruptedException e){
            e.printStackTrace();
        }
    }
}

存储值的对象：

/**
 * Created by 51304 on 2016/2/28.
 */
public class ValueObject {
    public static String value = "";
}

生产者线程：

/**
 * Created by 51304 on 2016/2/28.
 */
public class ThreadP extends Thread {
    private P p;
    public ThreadP(P p){
        this.p = p;
    }

    @Override
    public void run(){
        while (true){
            p.setValue();
        }
    }
}

消费者线程：

/**
 * Created by 51304 on 2016/2/28.
 */
public class ThreadC extends Thread {
    private C c;
    public ThreadC(C c){
        this.c = c;
    }

    @Override
    public void run(){
        while (true){
            c.getValue();
        }
    }
}

main方法：

/**
 * Created by 51304 on 2016/2/28.
 */
public class TestMain {
    public static void main(String[] args) {
        String lock = new String("");
        P p = new P(lock);
        C c = new C(lock);

        ThreadP threadP =new ThreadP(p);
        ThreadC threadC = new ThreadC(c);

        threadP.start();
        threadC.start();
    }
}

运行截图：

思考：如果多生产者和多消费者程序能正常工作吗？

答案是：程序会出现假死，也就是所有线程都停留在等待状态。出现这个现象的原因是，多生产者模式下notify()通知的线程还是生产者（选择通知那个线程时随机的，但只会通知一个），同理消费者也一样。当然解决的办法很明显使用notifyall().