Java多线程 Guarded Suspension设计模式

Java多线程 Guarded Suspension设计模式

目录1.Guarded Suspension模式的结构2. Guarded Suspension模式的简单实现

前言：

Guarded Suspension意bYTvpCfBs为保护暂停，其核心思想是仅当服务进程准备好时，才提供服务。设想一种场景，服务器可能会在很短时间内承受大量的客户端请求，客户端请求的数量可能超过服务器本身的即时处理能力，而服务端程序又不能丢弃任何一个客户请求。此时，最佳的处理方案莫过于让客户端要求进行排队，由服务端程序一个接一个处理。这样，既保证了所有的客户端请求均不丢失，同时也避免了服务器由于同时处理太多的请求而崩溃

1.Guarded Suspension模式的结构

Guarded Suspension模式的主要成员有：Request、RequestQueue、ClientThread、 ServerThread

Request：表示客户端请求

RequestQueue：用于保存客户端请求队列

ClientThread：客户端进程

ServerThread：服务器进程

其中，ClientThread负责不断发起请求，并将请求对象放入请求队列。ServerThread则根据其自身的状态，在有能力处理请求时，从RequestQueue中提取请求对象加以处理。

从流程图中可以看到，客户端的请求数量超过了服务线程的能力。在频繁的客户端请求中，RequestQueue充当了中间缓存，存放未处理的请求，保证了客户请求不丢失，同时也保护了服务线程不会受到大量并发的请求，而导致计算机资源不足

2. Guarded Suspension模式的简单实现

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;

this.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();

bYTvpCfBs }

}

}

}

public class Request {

private final String value;

public Request(String value) {

this.value = value;

}

public String getValue() {

return value;

}

}

public class RequestQueue {

private final LinkedList queue = new LinkedList<>();

public Request getRequest() {

synchronized (queue) {

while (queue.size() <= 0) {

try {

queue.wait();

} catch (InterruptedException e) {

return null;

}

}

return queue.removeFirst();

}

}

public void putRequest(Request request) {

synchronized (queue) {

queue.addLast(request);

queue.notifyAll();

}

}

}

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());

}

@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();

}

}

public class SuspensionClient {

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

final RequestQueue queue = new RequestQueue();

new ClientThread(queue,"Jack").start();

ServerThread serverThread = new ServerThread(queue);

serverThread.start();

Thread.sleep(10000);

serverThread.close();

}

}

运行:

Client -> request Jack

Server ->Jack

Client -> request Jack

Server ->Jack

Client -> request Jack

Server ->Jack

Client -> request Jack

Server ->Jack

Client -> request Jack

Client -> request Jack

Client -> request Jack

Server ->Jack

Client -> request Jack

Client -> request Jack

Server ->Jack

Client -> request Jack

Server ->Jack

Server ->Jack

Server ->Jack

Server ->Jack

Received the empty request.

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