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
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
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