Exchanger类详解

　　Exchanger并发辅助类，允许在并发任务之间交换数据。具体来说Exchanger类在两个线程之间定义同步点。当两个线程到达同步点时，它们交换数据结构。需要注意的是Exchanger类只能同步两个线程。

　　内存一致性效果：对于通过Exchanger成功交换对象的每对线程，每个线程中在exchanger()之前的操作 happen-before从另一线程中相应的exchanger()返回的后续操作。

下面用一对一的生产者-消费者例子进行说明。

　　生产者代码如下：

public class Producer implements Runnable {

    private List<String> buffer;

    private Exchanger<List<String>> exchanger;

    public Producer(List<String> buffer, Exchanger<List<String>> exchanger) {

        this.buffer = buffer;

        this.exchanger = exchanger;

    }

    @Override

    public void run() {

        int cycle=1;

        for (int i=0; i<10; i++) {

            System.out.println("Producer:Cycle "+cycle);

            for (int j = 1; j <=10; j++) {

                String msg="Event "+(i*10+j);

                System.out.println("Producer: "+msg);

                buffer.add(msg);

            }

            try {

                buffer=exchanger.exchange(buffer);//和消费者交换数据结构

            } catch (InterruptedException e) {

                e.printStackTrace();

            }

            System.out.println("Producer size: "+buffer.size());

            cycle++;

        }

    }

}

　　消费者代码：

public class Consumer implements Runnable {

    private List<String> buffer;

    private Exchanger<List<String>> exchanger;

    public Consumer(List<String> buffer, Exchanger<List<String>> exchanger) {

        this.buffer = buffer;

        this.exchanger = exchanger;

    }

    @Override

    public void run() {

        int cycle=1;

        for (int i=0; i<=9; i++) {

            System.out.println("Consumer: Cycle "+cycle);

            try {

                buffer=exchanger.exchange(buffer);//he生产者交换数据结构

            } catch (InterruptedException e) {

                e.printStackTrace();

            }

            System.out.println("Consumer size: "+buffer.size());

            for (int j = 1; j <=10; j++) {

                String msg=buffer.get(0);

                System.out.println("Consumer: "+msg);

                buffer.remove(0);

            }

            cycle++;

        }

    }

}

　　运行：

public class Core {

    public static void main(String[] args) {

        List<String> buffer1=new ArrayList<String>();

        List<String> buffer2=new ArrayList<String>();

        Exchanger<List<String>> exchanger=new Exchanger<List<String>>();

        Producer producer=new Producer(buffer1, exchanger);

        Consumer consumer=new Consumer(buffer2, exchanger);

        Thread thread1=new Thread(producer);

        Thread thread2=new Thread(consumer);

        thread1.start();

        thread2.start();

    }

}

巴特西

Exchanger类详解

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