Guarded Suspension Pattern

防卫暂停模式
Guarded Suspension Pattern的参与者：(对应Java设计模式中的"生产消费者模式")
GuardedObject(被防卫的对象)参与者，GuardedObject参与者是一个拥有被防卫的方法(guardedMethod)的类，当线程执行guardedMethod时，只要满足警戒条件，就会马上执行，但警戒条件不成立时，就要开始等待，警戒条件的成立与否，会随GuardedObject参与者的状态改变而变化；GuardedObject参与者除了guardedMethod以外，可能还会有用来更改实例状态(特别是用来更改警戒条件)的方法(stateChangingMethod)；Java语言中，使用while语句与wait方法来实现guardedMethod的，而是用notify/notifyAll方法来实现stateChangingMethod，在以下范例程序中，RequestQueue类就是GuardedObject参与者，getRequest方法与putRequest方法则分别是guardedMethod与stateChangingMethod
========Request类
public class Request {

private final String name;

public Request(String name) {
this.name = name;
}

public final String getName() {
return name;
}

public String toString() {
return "[ Request " + this.name + " ]";
}
}

=======RequestQueue类
public class RequestQueue {

private final LinkedList<Request> queue = new LinkedList();

public synchronized Request getRequest() {
try {
while (0 >= queue.size()) {
this.wait();
}
} catch (InterruptedException e) {
e.printStackTrace();
}
return (Request) queue.removeFirst();
}

public synchronized void putRequest(Request request) {
queue.addLast(request);
notifyAll();
}
}
=======ClientRequest类
public class ClientRequest extends Thread {

private Random random;
private RequestQueue queue;

public ClientRequest(RequestQueue queue, String name, long seed) {
super(name);
this.random = new Random(seed);
this.queue = queue;
}

public void run() {
try {
Request request = null;
for (int i = 0; i < 10000; i++) {
request = new Request("No." + i);
System.out.println(Thread.currentThread().getName()
+ " requests " + request);
queue.putRequest(request);
Thread.sleep(this.random.nextInt(1000));
}
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
=======ServerReqiest类
public class ServerRequest extends Thread {

private Random random;
private RequestQueue queue;

public ServerRequest(RequestQueue queue, String name, long seed) {
super(name);
this.queue = queue;
this.random = new Random(seed);
}

public void run() {
try {
Request request = null;
for (int i = 0; i < 10000; i++) {
request = queue.getRequest();
System.out.println(Thread.currentThread().getName()
+ " handles " + request);
Thread.sleep(this.random.nextInt(1000));
}
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
=========测试类
public class Main {

public static void main(String[] args) {
RequestQueue queue = new RequestQueue();
new ClientRequest(queue, "Alice", 3141592L).start();
new ServerRequest(queue, "Bobby", 6535897L).start();
}
}