Exchanger

Exchanger用于两个线程间交换数据。说起来这个和前面讲过的SynchronousQueue比较像。但是比
SynchronousQueue功能更强大的是可以双向交换数据。

image.png

在发生数据交换的时候的行为也和SynchronousQueue比较像:

1. 如果线程1想要和线程2交换数据，此时线程2并未准备好，那么此时线程1就会进入block状态
2. 线程2准备好，线程1解除block状态，发生数据交换

来个示例：

    public void testExchange() {
        Exchanger<String> stringExchanger = new Exchanger<>();

        CallThread callThread = new CallThread(stringExchanger);
        AnswerThread answerThread = new AnswerThread(stringExchanger);

        callThread.start();
        answerThread.start();
    }

    static class CallThread extends Thread {
        Exchanger<String> stringExchanger;

        public CallThread(Exchanger<String> stringExchanger) {
            setName("CallThread");
            this.stringExchanger = stringExchanger;
        }

        @Override
        public void run() {
            super.run();
            try {
                String call = stringExchanger.exchange("Call");
                System.out.println(Thread.currentThread().getName() + " " + call);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }

    static class AnswerThread extends Thread {
        Exchanger<String> stringExchanger;

        public AnswerThread(Exchanger<String> stringExchanger) {
            setName("AnswerThread");
            this.stringExchanger = stringExchanger;
        }

        @Override
        public void run() {
            super.run();
            try {
                String answer = stringExchanger.exchange("Answer");
                System.out.println(Thread.currentThread().getName() + " " + answer);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }

看下输出:

image.png

可以看到两个线程的数据发生了交换。