Java多執行緒16 Guarded Suspension設計模式
摘要：
Java多執行緒目錄
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...
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.