guarded-suspension模式

• guarded是“被保护着的”、“被防卫着的”意思。当现在并不适合马上执行某个操作时，就要求想要执行该操作的线程等待，以保障实例的安全性。（暂停的是服务器的端的线程）。

• Request

public class Request {
    final private String value;

    public Request(String value) {
        this.value = value;
    }

    public String getValue() {
        return value;
    }
}

• RequestQueue

public class RequestQueue {
    private  Queue<Request> queue = new LinkedList<>();
    public synchronized void putRequest(Request request){
        queue.offer(request);
        notifyAll();
    }
    public synchronized Request getRequest(){
        while (queue.peek() == null){
            try {
                wait();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        return queue.remove();
    }

}

• ClientThread

public class ClientThread extends Thread {

    private final RequestQueue queue;

    private final Random random;

    private final String sendValue;

    public ClientThread(RequestQueue queue, String sendValue) {
        this.queue = queue;
        this.sendValue = sendValue;
        random = new Random(System.currentTimeMillis());
    }

    @Override
    public void run() {
        for (int i = 0; i < 10; i++) {
            System.out.println("Client -> request " + sendValue);
            queue.putRequest(new Request(sendValue));
            try {
                Thread.sleep(random.nextInt(1000));
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
}

• ServerThread

public class ServerThread extends Thread {

    private final RequestQueue queue;

    private final Random random;

    private volatile boolean closed = false;

    public ServerThread(RequestQueue queue) {
        this.queue = queue;
        random = new Random(System.currentTimeMillis());
    }

    /**
     * server三种被中断的方式：
     * 1：正要运行的时候发现closed标识已经为true了
     * 2：处于wait状态。closed起不到作用，调用close方法中断，request返回null
     * 3: sleep的时候被中断
     */
    @Override
    public void run() {
        while (!closed) {
            Request request = queue.getRequest();
            if (null == request) {
                System.out.println("Received the empty request.");
                continue;
            }
            System.out.println("Server ->" + request.getValue());
            try {
                Thread.sleep(random.nextInt(1000));
            } catch (InterruptedException e) {
                return;
            }
        }
    }

    public void close() {
        this.closed = true;
        this.interrupt();
    }
}

• 调用类

public class SuspensionClient {
    public static void main(String[] args) throws InterruptedException {

        final RequestQueue queue = new RequestQueue();
        new ClientThread(queue, "Alex").start();
        ServerThread serverThread = new ServerThread(queue);
        serverThread.start();
        //serverThread.join();

        Thread.sleep(10000);
        serverThread.close();
    }
}