Concurrent -- 08 -- Exchanger用法解析

Gene Xu

于 2020-07-26 15:48:50 发布

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分类专栏： Thread 文章标签： Exchanger

本文链接：https://blog.youkuaiyun.com/Goodbye_Youth/article/details/107594577

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原文链接：Concurrent – 08 – Exchanger用法解析

Exchanger，即交换器，是一个同步工具类，用于控制两个线程在同步点处的数据交换

Exchanger 提供了一个同步点 (调用 exchange() 方法的地方即为同步点)，当一个线程先执行到达同步点后，会被阻塞，直到另一个线程也进入到同步点为止，当两个线程都到达该同步点后，就会进行数据交换

举例说明 1

ExchangerTest.java

public class ExchangerTest {

    public static void main(String[] args) {
        Exchanger<String> exchanger = new Exchanger<>();
        new Thread(new Boy(exchanger)).start();
        new Thread(new Girl(exchanger)).start();
        
        // 女生慢慢地从教室里走出来...
        // 男生说：【我其实暗恋你很久了...】
        // 女生说：【我很喜欢你...】
    }
}

class Boy implements Runnable {

    private Exchanger<String> exchanger;

    public Boy(Exchanger<String> exchanger) {
        this.exchanger = exchanger;
    }

    @Override
    public void run() {
        try {
            System.out.println("女生慢慢地从教室里走出来...");
            TimeUnit.SECONDS.sleep(2);
            // 男生对女生说的话
            String boy = exchanger.exchange("我很喜欢你...");
            System.out.println("男生说：【" + boy +"】");
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

class Girl implements Runnable {

    private Exchanger<String> exchanger;

    public Girl(Exchanger<String> exchanger) {
        this.exchanger = exchanger;
    }
    
    @Override
    public void run() {
        try {
            // 女生对男生说的话
            String girl = exchanger.exchange("我其实暗恋你很久了...");
            System.out.println("女生说：【" + girl +"】");
        } catch (Exception e) {  
            e.printStackTrace();  
        } 
    }
}

如上所示，调用 exchange() 方法会阻塞当前线程，使其进入同步点，当另一个线程也调用 exchange() 方法到达同步点后，两者就会进行数据交换

举例说明 2

ExchangerTest.java

public class ExchangerTest {

    public static void main(String[] args) {
        Exchanger<String> exchanger = new Exchanger<>();
        new Thread(new Boy(exchanger)).start();
        new Thread(new Girl(exchanger)).start();
        
        // 女生慢慢地从教室里走出来...
        // java.util.concurrent.TimeoutException
        //      at java.util.concurrent.Exchanger.exchange(Exchanger.java:626)
        //      at com.xj.current.tool.Girl.run(ExchangerTest.java:55)
        //      at java.lang.Thread.run(Thread.java:748)

    }
}

class Boy implements Runnable {

    private Exchanger<String> exchanger;

    public Boy(Exchanger<String> exchanger) {
        this.exchanger = exchanger;
    }

    @Override
    public void run() {
        try {
            System.out.println("女生慢慢地从教室里走出来...");
            TimeUnit.SECONDS.sleep(2);
            // 男生对女生说的话
            String boy = exchanger.exchange("我很喜欢你...");
            System.out.println("男生说：【" + boy +"】");
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

class Girl implements Runnable {

    private Exchanger<String> exchanger;

    public Girl(Exchanger<String> exchanger) {
        this.exchanger = exchanger;
    }
    
    @Override
    public void run() {
        try {
            // 女生对男生说的话
            String girl = exchanger.exchange("我其实暗恋你很久了...", 1, TimeUnit.SECONDS);
            System.out.println("女生说：【" + girl +"】");
        } catch (Exception e) {  
            e.printStackTrace();  
        } 
    }
}