Worker Thread模式--工作沒來就一直等，工作來了就幹活

定義：

Worker Thread模式也叫背景模式或者線程池模式，工作線程逐個取回並處理，在所有工作完全完成後，線程等待新的工作到來。

引例：

類的一覽表

名字	說明
main	測試行爲類
clientthread	表示發出工作的類
request	表示工作請求的類
channel	接受工作並將工作請求交給工人線程
workerthread	工人線程類

public class Main {
    public static void main(String[] args) {
        Channel channel = new Channel(5);   // 工人線程的數量
        channel.startWorkers();
        new ClientThread("Alice", channel).start();
        new ClientThread("Bobby", channel).start();
        new ClientThread("Chris", channel).start();
    }
}

public class Request {
    private final String name; //  委託者
    private final int number;  // 請求編號
    private static final Random random = new Random();
    public Request(String name, int number) {
        this.name = name;
        this.number = number;
    }
    public void execute() {
        System.out.println(Thread.currentThread().getName() + " executes " + this);
        try {
            Thread.sleep(random.nextInt(1000));
        } catch (InterruptedException e) {
        }
    }
    public String toString() {
        return "[ Request from " + name + " No." + number + " ]";
    }
}

public class Channel {
    private static final int MAX_REQUEST = 100;
    private final Request[] requestQueue;
    private int tail;  // 下一個putRequest的地方
    private int head;  // 下一個takeRequest的地方
    private int count; // Request的數量

    private final WorkerThread[] threadPool;

    public Channel(int threads) {
        this.requestQueue = new Request[MAX_REQUEST];
        this.head = 0;
        this.tail = 0;
        this.count = 0;

        threadPool = new WorkerThread[threads];
        for (int i = 0; i < threadPool.length; i++) {
            threadPool[i] = new WorkerThread("Worker-" + i, this);
        }
    }
    public void startWorkers() {
        for (int i = 0; i < threadPool.length; i++) {
            threadPool[i].start();
        }
    }
    public synchronized void putRequest(Request request) {
        while (count >= requestQueue.length) {
            try {
                wait();
            } catch (InterruptedException e) {
            }
        }
        requestQueue[tail] = request;
        tail = (tail + 1) % requestQueue.length;
        count++;
        notifyAll();
    }
    public synchronized Request takeRequest() {
        while (count <= 0) {
            try {
                wait();
            } catch (InterruptedException e) {
            }
        }
        Request request = requestQueue[head];
        head = (head + 1) % requestQueue.length;
        count--;
        notifyAll();
        return request;
    }
}

 

public class ClientThread extends Thread {
    private final Channel channel;
    private static final Random random = new Random();
    public ClientThread(String name, Channel channel) {
        super(name);
        this.channel = channel;
    }
    public void run() {
        try {
            for (int i = 0; true; i++) {
                Request request = new Request(getName(), i);
                channel.putRequest(request);
                Thread.sleep(random.nextInt(1000));
            }
        } catch (InterruptedException e) {
        }
    }
}

public class WorkerThread extends Thread {
    private final Channel channel;
    public WorkerThread(String name, Channel channel) {
        super(name);
        this.channel = channel;
    }
    public void run() {
        while (true) {
            Request request = channel.takeRequest();
            request.execute();
        }
    }
}

結果： 

 Worker-1 executes [ Request from Alice No.0 ]
Worker-3 executes [ Request from Bobby No.0 ]
Worker-0 executes [ Request from Chris No.0 ]
Worker-2 executes [ Request from Alice No.1 ]
Worker-4 executes [ Request from Bobby No.1 ]
Worker-1 executes [ Request from Alice No.2 ]
Worker-4 executes [ Request from Chris No.1 ]
Worker-3 executes [ Request from Bobby No.2 ]
Worker-0 executes [ Request from Bobby No.3 ]
Worker-4 executes [ Request from Alice No.3 ]

 Worker Thread模式中的角色

client（委託者）：client角色創建請求的request角色，並將其傳遞給channel角色。

channel（通信線路）：channel角色接收client傳遞過來的request角色，並傳遞給worker角色。

worker（工人）：worker角色從channel獲得request角色並工作。

request（請求）：表示工作。