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Java中的多個消費者生產者

[英]Multiple Consumer Producer In Java

 原文  2018-08-29 17:28:01  6   1    java/ multithreading/ producer-consumer

問題描述

我試圖為消費者創建2個線程，為生產者創建2個線程。 所有4個線程都在爭用一種資源。 其中兩個試圖從資源中消費，而兩個試圖生產。

下面是代碼 

package com.threading;

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

public class TestConsumerProducer2 {

    protected static int maxSize = 2;

    static class Consumer implements Runnable {
        List<Integer> goods;

        public Consumer(List<Integer> goods) {
            this.goods = goods;
        }

        public void consume() {
            synchronized (goods) {

                if (goods.size() <= 0) {
                    try {
                        goods.wait();
                    } catch (InterruptedException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }
                }
                System.out.println(Thread.currentThread().getName() + " >>>> consuming >>>" + goods.remove(0));
                goods.notifyAll();
            }
        }

        @Override
        public void run() {
            for (int i = 0; i < 10; i++) {
                consume();
                try {
                    Thread.currentThread().sleep(100);
                } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
        }
    }

    static class Producer implements Runnable {
        List<Integer> goods;

        public Producer(List<Integer> goods) {
            this.goods = goods;
        }

        public void produce(int i) {
            synchronized (goods) {

                if (goods.size() >= maxSize) {
                    try {
                        goods.wait();
                    } catch (InterruptedException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }
                }
                System.out.println(Thread.currentThread().getName() + ">>> producing >> " + i);
                goods.add(i);
                goods.notifyAll();
            }
        }

        @Override
        public void run() {
            // TODO Auto-generated method stub
            for (int i = 0; i < 10; i++) {
                produce(i);
                try {
                    Thread.currentThread().sleep(100);
                } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
        }
    }

    public static void main(String[] args) {
        List<Integer> goods = new ArrayList<>();
        Consumer consumer = new Consumer(goods);
        Producer producer = new Producer(goods);
        Thread consumerWorker1 = new Thread(consumer);
        Thread consumerWorker2 = new Thread(consumer);

        Thread prroducerWorker1 = new Thread(producer);
        Thread prroducerWorker2 = new Thread(producer);

        consumerWorker1.start();
        consumerWorker2.start();
        prroducerWorker1.start();
        prroducerWorker2.start();

        try {
            consumerWorker1.join();
            consumerWorker2.join();
            prroducerWorker1.join();
            prroducerWorker2.join();
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

        System.out.println("Job completed >>>>");
    }
}

程序輸出

線程2 >>>生產>> 0

線程1 >>>>消耗>>> 0

線程3 >>>生產>> 0

線程“ Thread-0”中的異常java.lang.IndexOutOfBoundsException：Index：0，Size：0 at java.util.ArrayList.rangeCheck（ArrayList.java:657）at java.util.ArrayList.remove（ArrayList.java:496） ）在com.threading.TestConsumerProducer2 $ Consumer.consume（TestConsumerProducer2.java:27）在com.threading.TestConsumerProducer2 $ Consumer.run（TestConsumerProducer2.java:35）在java.lang.Thread.run（Thread.java:748）線程2 >>>生產>> 1

線程1 >>>>消耗>>> 0

線程3 >>>生產>> 1

線程1 >>>>消耗>>> 1

線程2 >>>生產>> 2

線程1 >>>>消耗>>> 1

線程3 >>>生產>> 2

線程1 >>>>消耗>>> 2

線程2 >>>生產>> 3

線程1 >>>>消耗>>> 2

線程2 >>>生產>> 4

線程3 >>>生產>> 3

線程1 >>>>消耗>>> 3

線程2 >>>生產>> 5

線程1 >>>>消耗>>> 4

線程3 >>>生產>> 4

線程1 >>>>消耗>>> 3

線程2 >>>生產>> 6線程1 >>>>消耗>>> 5

線程2 >>>生產>> 7

線程3 >>>生產>> 5

問題陳述：為什么沒有一個線程執行10次？ 代碼中的死鎖情況在哪里？ 當商品對象被使用者線程鎖定並且size <= 0時，為什么應該進入等待狀態，為什么會有IndexOutOfBoundsException？

1 個解決方案

解決方案1
 3 已采納  2018-08-29 18:12:48

更改代碼中if到while出現可解決此問題。

在Oracle網站上的“ Guarded Blocks”教程中有相關建議：

注意：始終在循環中調用wait，以測試正在等待的條件。 不要以為中斷是針對您正在等待的特定條件，還是該條件仍然為真。

（通過中斷，它們表示從等待中返回，而不一定是源自調用Thread.interrupt的人的實際中斷。）

關鍵點：

  • 線程僅在檢查時擁有鎖時才知道商品清單的內容。

  • 調用wait會放棄該鎖，從而允許其他線程在此線程處於休眠狀態時取得進展。

  • 一旦線程放棄了鎖，先前對商品清單狀態所做的任何檢查將不再有效。

線程從等待狀態返回后，它已經重新獲得了鎖，但是線程需要重新評估條件檢查，否則它將作用於陳舊的信息。 在線程上次檢查條件的時間與當前時間之間可能發生了很多事情。 之所以會得到IllegalArgumentException，是因為當前線程假設在等待當前線程時，有另一個線程刪除了該線程。 

package com.threading;

import java.util.ArrayList; 

import java.util.List;

public class TestConsumerProducer2 {

protected static int maxSize = 2;

static class Consumer implements Runnable {
    List<Integer> goods;

    public Consumer(List<Integer> goods) {
        this.goods = goods;
    }

    public void consume() {
        synchronized (goods) {

            while (goods.size() <= 0) {
                try {
                    goods.wait();
                } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
            System.out.println(Thread.currentThread().getName() + " >>>> consuming >>>" + goods.remove(0));
            goods.notifyAll();
        }
    }

    @Override
    public void run() {
        for (int i = 0; i < 10; i++) {
            consume();
            try {
                Thread.currentThread().sleep(100);
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
    }
}

static class Producer implements Runnable {
    List<Integer> goods;

    public Producer(List<Integer> goods) {
        this.goods = goods;
    }

    public void produce(int i) {
        synchronized (goods) {

            while (goods.size() >= maxSize) {
                try {
                    goods.wait();
                } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
            System.out.println(Thread.currentThread().getName() + ">>> producing >> " + i);
            goods.add(i);
            goods.notifyAll();
        }
    }

    @Override
    public void run() {
        // TODO Auto-generated method stub
        for (int i = 0; i < 10; i++) {
            produce(i);
            try {
                Thread.currentThread().sleep(100);
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
    }
}

public static void main(String[] args) {
    List<Integer> goods = new ArrayList<>();
    Consumer consumer = new Consumer(goods);
    Producer producer = new Producer(goods);
    Thread consumerWorker1 = new Thread(consumer);
    Thread consumerWorker2 = new Thread(consumer);

    Thread prroducerWorker1 = new Thread(producer);
    Thread prroducerWorker2 = new Thread(producer);

    consumerWorker1.start();
    consumerWorker2.start();
    prroducerWorker1.start();
    prroducerWorker2.start();

    try {
        consumerWorker1.join();
        consumerWorker2.join();
        prroducerWorker1.join();
        prroducerWorker2.join();
    } catch (InterruptedException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

    System.out.println("Job completed >>>>");
}

}

代碼現在成功完成，輸出如下： 

C:\>java com.threading.TestConsumerProducer2
Thread-2>>> producing >> 0
Thread-1 >>>> consuming >>>0
Thread-3>>> producing >> 0
Thread-0 >>>> consuming >>>0
Thread-2>>> producing >> 1
Thread-3>>> producing >> 1
Thread-0 >>>> consuming >>>1
Thread-1 >>>> consuming >>>1
Thread-2>>> producing >> 2
Thread-3>>> producing >> 2
Thread-0 >>>> consuming >>>2
Thread-1 >>>> consuming >>>2
Thread-2>>> producing >> 3
Thread-0 >>>> consuming >>>3
Thread-3>>> producing >> 3
Thread-1 >>>> consuming >>>3
Thread-2>>> producing >> 4
Thread-0 >>>> consuming >>>4
Thread-3>>> producing >> 4
Thread-1 >>>> consuming >>>4
Thread-2>>> producing >> 5
Thread-0 >>>> consuming >>>5
Thread-3>>> producing >> 5
Thread-1 >>>> consuming >>>5
Thread-2>>> producing >> 6
Thread-0 >>>> consuming >>>6
Thread-3>>> producing >> 6
Thread-1 >>>> consuming >>>6
Thread-2>>> producing >> 7
Thread-0 >>>> consuming >>>7
Thread-3>>> producing >> 7
Thread-1 >>>> consuming >>>7
Thread-2>>> producing >> 8
Thread-0 >>>> consuming >>>8
Thread-3>>> producing >> 8
Thread-1 >>>> consuming >>>8
Thread-2>>> producing >> 9
Thread-0 >>>> consuming >>>9
Thread-3>>> producing >> 9
Thread-1 >>>> consuming >>>9
Job completed >>>>

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