前言：
Guarded Suspension意为保护暂停，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
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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
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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(); } } }} |
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public class Request { private final String value; public Request(String value) { this.value = value; } public String getValue() { return value; }} |
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public class RequestQueue { private final LinkedList<Request> 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(); } }} |
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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(); }} |
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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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原文链接：https://juejin.cn/post/7022609159912685575
