Java多线程设计模式（二）

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mb5fe1902d5617a 2013-09-15 01:06:00

文章标签 java ide i++ 数据构造函数 文章分类 代码人生

目录(?)[-]

Guarded Suspension Pattern
Balking Pattern
Producer-Consumer Pattern

Guarded Suspension Pattern

该模式描述的是当一个线程在执行某个操作时，但由于其他资源还没有准备好，需要等待，那么就等待资源准备好才开始自己的操作。我们直接看代码例子：

[java] view plaincopy

public class Request {
private Stringname;
public Request(String name) {
this.name = name;
}
public String getName() {
returnname;
}
@Override
public String toString() {
return"[ Request " +name +" ]";
}
}
public class RequestQueue {
final private LinkedList<request>queue = new LinkedList<request>();
public synchronizedvoid putRequest(Request request) {
this.queue.addLast(request);
notifyAll();
}
publicsynchronized Request getRequest() {
// 多线程版本的if
while (this.queue.size() <= 0) {
try {
wait();
}catch (InterruptedException e) {
}
}
return queue.removeFirst();
}
}
import java.util.Random;
public class ClientThreadextends Thread {
private Random random;
private RequestQueuerequestQueue;
public ClientThread(RequestQueue requestQueue, String name,long seed) {
super(name);
this.requestQueue = requestQueue;
this.random =new Random(seed);
}
@Override
public void run() {
for (int i = 0; i < 10000; i++) {
Request request = new Request("No." + i);
System.out.println(Thread.currentThread().getName() +" requests " + request);
this.requestQueue.putRequest(request);
try {
Thread.sleep(this.random.nextInt(1000));
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}
import java.util.Random;
public class ServerThreadextends Thread {
private Random random;
private RequestQueuequeue;
public ServerThread(RequestQueue queue, String name,long seed) {
super(name);
this.queue = queue;
random =new Random(seed);
}
@Override
public void run() {
for (int i = 0; i < 10000; i++) {
Request request = queue.getRequest();
System.out.println(Thread.currentThread().getName() +" handles " + request);
try {
Thread.sleep(random.nextInt(1000));
} catch (InterruptedException e) {
}
}
}
}
public class Main {
public static void main(String[] args) {
RequestQueue queue = new RequestQueue();
ServerThread serverThread = new ServerThread(queue,"ServerThread", 3141592l);
ClientThread clientThread = new ClientThread(queue,"ClientThread", 6535897l);
serverThread.start();
clientThread.start();
}
}
</request></request>

这段代码的关键在 ReqeustQueue类的getReqeust()方法，在该方法中，判断队列是否小于或等于0，如果是，那么就等待队列有数据之后在进行获取 Request对象的操作，注意这里使用的是while，而非if。Single Threaded Execution Pattern 只有一个线程可以进入临界区，其他线程不能进入，进行等待；而Guarded Suspension Pattern中，线程要不要等待，由警戒条件决定。只有RequestQueue类使用到了wait/notifyAll，Guarded Suspension Pattern的实现是封闭在RequestQueue类里的。
Balking Pattern

该模式的重点是，如果一个请求的资源状态还没有准备好，那么就不进行处理，直接返回，它与Guarded Suspension Pattern的区别在于Guarded Suspension Pattern在警戒条件不成立时，线程等待，而Balking Pattern线程直接返回。我们来看代码实现：

[java] view plaincopy