Suspension模式 --等我準備好

定義：

Suspension模式通過線程等待來保證實例的安全性。

引例

類的一覽表

名字	說明
Request	請求類
RequestQueue	依次存放求情的類
ClientThread	發送請求類
ServerThread	接受請求類
Main	測試行爲類

public class Request {
	private final String name;

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

	public String getName() {
		return name;
	}

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

public class RequestQueue {
	// 有點像消息隊列。生產者與消費者
	private final LinkedList queue = new LinkedList();

	public synchronized Request getRequest() {
		while (queue.size() <= 0) {
			try {
				// 隊列爲空則等待阻塞
				wait();
			} catch (InterruptedException e) {
			}
		}
		return (Request) queue.removeFirst();
	}

	public synchronized void putRequest(Request request) {
		queue.addLast(request);
		notifyAll();
	}
}

public class ClientThread extends Thread {
	private Random random;
	private RequestQueue requestQueue;

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

	public void run() {
		for (int i = 0; i < 10000; i++) {
			Request request = new Request("No." + i);
			System.out.println(Thread.currentThread().getName() + " requests " + request);
			requestQueue.putRequest(request);
			try {
				Thread.sleep(random.nextInt(1000));
			} catch (InterruptedException e) {
			}
		}
	}
}

public class ServerThread extends Thread {
	private Random random;
	private RequestQueue requestQueue;

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

	public void run() {
		for (int i = 0; i < 10000; i++) {
			Request request = requestQueue.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 requestQueue = new RequestQueue();
		new ClientThread(requestQueue, "Alice", 3141592L).start();
		new ServerThread(requestQueue, "Bobby", 6535897L).start();
	}
}

結果： 

Alice requests [ Request No.0 ]
Bobby handles  [ Request No.0 ]
Alice requests [ Request No.1 ]
Alice requests [ Request No.2 ]
Bobby handles  [ Request No.1 ]
Bobby handles  [ Request No.2 ]
Alice requests [ Request No.3 ]
Bobby handles  [ Request No.3 ]
Alice requests [ Request No.4 ]
Bobby handles  [ Request No.4 ]
Alice requests [ Request No.5 ]
Alice requests [ Request No.6 ]

 Suspension模式 中的角色

GuardedObject（被守護的對象）是一個持有被守護方法的類。當線程執行守護方法時，若守護條件成立則執行，若不成立則等待。守護條件的成立會隨着被守護的對象狀態發生改變。