Question

The following source code are used to implement product/consumer pattern, but they don’t work well, and I don’t know how to solve it.

class 1:productor

package test;

import java.util.ArrayList;
import java.util.List;

public class Productor extends Thread {

private List list = null;

public Productor(ArrayList list) {
    this.list = list;
}

public synchronized void product() throws InterruptedException {
    for (int e = 0; e < 10; e++) {
        System.out.println("Add-" + e + "  " + System.currentTimeMillis());
        list.add(e);

        if (list.size() >= 10) {
            wait();
        } else {
            notifyAll();
        }
    }
}

public void run() {
    try {
        while(true){
            product();
        }
    } catch (Exception e) {
        e.printStackTrace();
    }
}
}

class 2:Consumer
package test;

import java.util.ArrayList;
import java.util.List;

public class Consumer extends Thread {

private List list = null;

public Consumer(ArrayList list) {
    this.list = list;
}

public synchronized void consume() throws InterruptedException {
    if (list.size() <= 0) {
        wait();
    } else {
        notifyAll();
    }

    for (int e = 0; e < list.size(); e++) {
        System.out.println("Remove-" + e + "  "
                + System.currentTimeMillis());
        list.remove(e);
    }
}

public void run() {
    try {
        while(true){
            consume();
        }
    } catch (Exception e) {
        e.printStackTrace();
    }
}

}

class 3:Testing for product/consumer
package test;

import java.util.ArrayList;

public class TestCP {
public static void main(String args[]) throws InterruptedException {
    ArrayList product = new ArrayList();
    Productor pt = new Productor(product);
    Consumer ct = new Consumer(product);
    pt.start();
    ct.start();
}
}

The output of TestCP is :

Add-0 1340777963967

Add-1 1340777963968

Add-2 1340777963968

Add-3 1340777963968

Add-4 1340777963968

Add-5 1340777963968

Add-6 1340777963968

Add-7 1340777963968

Add-8 1340777963968

Add-9 1340777963968

My intent is that Productor products 10 elements that stored in a list and consumed by Consumer, then Productor products elements again, Consumer consumes again…
Any feedback will be appreciated, thanks.

Answer 1

You wait/notify on the diferent thread not on the list. So the threads are running on their own monitors not on a shared one. Search for “java wait notify” and keep on reading.