Java多线程之 使用Exchanger在线程之间交换数据

               

在多线程中，两个线程之间交换数据是非常常见的情况，我们可以使用公共的数据结构，同样，Java也提供了很好

的类供我们使用，那就是Exchanger类，这个类可以帮助我们在两个线程之间同步数据结构，下面我们以这个类再来实

现一遍生产者消费者模型，貌似这个模型已经被写烂了。

package com.bird.concursey.charpet5;import java.util.List;import java.util.concurrent.Exchanger;public class Producer implements Runnable { //This will be the data structure that the producer will interchange with the consumer. private List buffer;  private Exchanger> exchanger;  public Producer(List buffer, Exchanger> exchanger) {  super();  this.buffer = buffer;  this.exchanger = exchanger; } @Override public void run() {  int cycle = 1;  for(int i = 0; i < 10; i++) {   System.out.printf("Producer: Cycle %d\n",cycle);   for (int j=0; j<10; j++){    String message="Event "+((i*10)+j);    System.out.printf("Producer: %s\n",message);    buffer.add(message);   }   try {    buffer = exchanger.exchange(buffer);   } catch (InterruptedException e) {    // TODO Auto-generated catch block    e.printStackTrace();   }   System.out.println("Producer: "+buffer.size());   cycle++;  } }}

package com.bird.concursey.charpet5;import java.util.ArrayList;import java.util.List;import java.util.concurrent.Exchanger;public class Consumer implements Runnable {  private List buffer;  private Exchanger> exchange;  public Consumer(List buffer, Exchanger> exchange) {  super();  this.buffer = buffer;  this.exchange = exchange; } @Override public void run() {  int cycle = 1;  for(int i = 0; i < 10; i++) {   System.out.printf("Consumer: Cycle %d\n",cycle);   try {    buffer = exchange.exchange(buffer);   } catch (InterruptedException e) {    e.printStackTrace();   }   System.out.println("Consumer: "+buffer.size());   for (int j=0; j<10; j++){    String message=buffer.get(0);    System.out.println("Consumer: "+message);    buffer.remove(0);   }   cycle++;  } }  public static void main(String[] args) {  List buffer1 = new ArrayList();  List buffer2 = new ArrayList();    Exchanger> exchange = new Exchanger>();    Producer producer = new Producer(buffer1, exchange);  Consumer consumer = new Consumer(buffer2, exchange);    Thread threadProducer=new Thread(producer);  Thread threadConsumer=new Thread(consumer);    threadProducer.start();  threadConsumer.start(); }}

The consumer begins with an empty buffer and calls Exchanger to synchronize with theproducer. It needs data to consume. The producer begins its execution with an empty buffer.It creates 10 strings, stores it in the buffer, and uses the exchanger to synchronize withthe consumer.

At this point, both threads (producer and consumer) are in Exchanger and it changes thedata structures, so when the consumer returns from the exchange() method, it will have abuffer with 10 strings. When the producer returns from the exchange() method, it will havean empty buffer to fill again. This operation will be repeated 10 times.

If you execute the example, you will see how producer and consumer do their jobsconcurrently and how the two objects interchange their buffers in every step. As it occurs withother synchronization utilities, the first thread that calls the exchange() method was put tosleep until the other threads arrived.

           

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