Java多線程基礎（十）——Work Thread模式

1、定義

Work Thread模式和Thread-Per-Message模式相似，Thread-Per-Message每次都建立一個新的線程處理請求，而Work Thread模式預先會建立一個線程池（Thread Pool），每次從線程池中取出線程處理請求。

2、模式案例

Request請求類：

public class Request {
    private final String name;
    private final int number;
    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 + " ]";
    }
}

Client線程類：
Client線程類用來送出請求：

• 建立Request實例
• 將這個實例傳送給Channel類的putRequest方法

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) {
        }
    }
}

Worker線程類：
WorkerThread類表示工人線程，工人線程能夠執行如下動做：

• 從Channel實例取出Request實例
• 調用Request實例的execute方法

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();
        }
    }
}

Channel類：

/**
 *Channel類可用來接受、傳送工做請求，並保存工人線程。
 */
public class Channel {
    private static final int MAX_REQUEST = 100; // 最大請求數
    private final Request[] requestQueue;         // 請求隊列
    private int tail;
    private int head;
    private int count;
    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;
    }
}

執行：

public class Main {
    public static void main(String[] args) {
        Channel channel = new Channel(5);
        channel.startWorkers();
        new ClientThread("Alice", channel).start();
        new ClientThread("Bobby", channel).start();
        new ClientThread("Chris", channel).start();
    }
}

3、模式講解

Work Thread模式的角色以下：

• Client（委託人）參與者

Client參與者會建立請求(Request)，而後傳送給Channel參與者。

• Channel（通道）參與者

Channel參與者保存Request請求隊列，同時會預建立Worker線程。

• Worker（工人）參與者

Worker參與者會從Channel獲取Request。

• Request（請求）參與者

Worker參與者會從Channel獲取Request。

注：啓動線程是一項繁重的工做，Worker Thread模式預先建立一批線程，能夠重複使用線程，達到資源再利用、提高性能的目的。