Java多執行緒16 Guarded Suspension設計模式
Guarded Suspension意為保護暫停,其核心思想是僅當服務程序準備好時,才提供服務。設想一種場景,伺服器可能會在很短時間內承受大量的客戶端請求,客戶端請求的數量可能超過伺服器本身的即時處理能力,而服務端程式又不能丟棄任何一個客戶請求。此時,最佳的處理方案莫過於讓客戶端要求進行排隊,由服務端程式一個接一個處理。這樣,既保證了所有的客戶端請求均不丟失,同時也避免了伺服器由於同時處理太多的請求而崩潰
1.Guarded Suspension模式的結構
Guarded Suspension模式的主要成員有:Request、RequestQueue、ClientThread、 ServerThread
Request:表示客戶端請求
RequestQueue:用於儲存客戶端請求佇列
ClientThread:客戶端程序
ServerThread:伺服器程序
其中,ClientThread負責不斷髮起請求,並將請求物件放入請求佇列。ServerThread則根據其自身的狀態,在有能力處理請求時,從RequestQueue中提取請求物件加以處理。
從流程圖中可以看到,客戶端的請求數量超過了服務執行緒的能力。在頻繁的客戶端請求中,RequestQueue充當了中間快取,存放未處理的請求,保證了客戶請求不丟失,同時也保護了服務執行緒不會受到大量併發的請求,而導致計算機資源不足
2. Guarded Suspension模式的簡單實現
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(); } } } }
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<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(); } } }
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(); } }
執行
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.