Exchanger的理解和使用

一、简介

Exchanger用于两个线程之间进行数据交换，每个线程调用exchage方法到达各自的同步点，当且仅当两个线程都达到同步点的时候，才可以交换信息，否则先到达同步点的线程必须等待。

二、使用案例

    public static void main(String[] args) {
        Exchanger<String> exchanger = new Exchanger<>();
        Thread thread1 = new Thread(new Runnable() {
            @Override
            public void run() {
                String method1 = "method1";
                log.info("线程1到达同步点...");
                try {
                    String strFromThread2 = exchanger.exchange(method1);
                    log.info("线程1获取的交换数据是{}", strFromThread2);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                log.info("线程1运行结束");
            }
        });

        Thread thread2 = new Thread(new Runnable() {
            @Override
            public void run() {
                String method2 = "method2";
                try {
                    log.info("线程2开始执行...");
                    // 让线程1先达到同步点
                    TimeUnit.SECONDS.sleep(3);
                    log.info("线程2达到同步点...");
                    String strFromThread1 = exchanger.exchange(method2);
                    log.info("线程2获取的交换数据是{}", strFromThread1);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                log.info("线程2运行结束");
            }
        });

        thread1.start();
        thread2.start();
    }

运行结果如下：

03:02:43.733 [Thread-0] INFO com.example.concurrent.ExchangerTest - 线程1到达同步点...
03:02:43.733 [Thread-1] INFO com.example.concurrent.ExchangerTest - 线程2开始执行...
03:02:46.740 [Thread-1] INFO com.example.concurrent.ExchangerTest - 线程2达到同步点...
03:02:46.740 [Thread-1] INFO com.example.concurrent.ExchangerTest - 线程2获取的交换数据是method1
03:02:46.740 [Thread-0] INFO com.example.concurrent.ExchangerTest - 线程1获取的交换数据是method2
03:02:46.749 [Thread-1] INFO com.example.concurrent.ExchangerTest - 线程2运行结束
03:02:46.749 [Thread-0] INFO com.example.concurrent.ExchangerTest - 线程1运行结束

需要注意的是，Exchanger仅可用作两个线程之间的信息交换，当超过2个线程调用同一个Exchanger时，得到的结果是不可预料的。