调度模式·Worker-Channel-Request

以下代码在《Java多线程设计模式》(结城浩著，博硕文化译，中国铁道出版社，2005）第8章"Worler Thread －－等到工作来，来了就工作"代码基础上改进而得。

改动主要为：
（1）提炼了IRequest接口
（2）添加了终结工作线程的方法。

参与者：
Client--委托方。
Channel--生产线
Request--生产任务
WorkerThread--工作线程

委托方把Request放入Channel中。Worker从Channel中取出Request，进行加工。

代码：

Channel.java

public class Channel
{
    private static final int MAX_REQUEST = 100;

    private final IRequest[] requestQueue;

    private int tail; // 下一个putRequest的地方

    private int head; // 下一个takeRequest的地方

    private int count; // Request的数量
    
    private boolean stoped = true;

    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(this);
        }
    }

    public void startWorkers()
    {
        this.stoped = false;
        for (int i = 0; i < threadPool.length; i++)
        {
            threadPool[i].start();
        }
    }
    
    public synchronized int getCount()
    {
        return this.count;
    }
    
    public synchronized boolean isStoped()
    {
        return this.stoped;
    }
    
    public synchronized void stopWorkers()
    {
        this.stoped = true;
    }

    public synchronized void putRequest(IRequest request)
    {
        while (count >= requestQueue.length)
        {
            try
            {
                wait();
            }
            catch (InterruptedException e)
            {
            }
        }
        requestQueue[tail] = request;
        tail = (tail + 1) % requestQueue.length;
        count++;
        notifyAll();
    }

    public synchronized IRequest takeRequest()
    {
        while (count <= 0)
        {
            try
            {
                wait();
            }
            catch (InterruptedException e)
            {
            }
        }
        IRequest request = requestQueue[head];
        head = (head + 1) % requestQueue.length;
        count--;
        notifyAll();
        return request;
    }
}

IRequest.java

public interface IRequest
{
    public abstract void execute() throws Exception;
}

WorkerThread.java

public class WorkerThread extends Thread
{
    private final Channel channel;

    public WorkerThread(Channel channel)
    {
        this.channel = channel;
    }

    public void run()
    {
        System.out.println("[Thread]: WorkerThread " + this.getName()
                + " start!");

        while (true)
        {
            if (channel.getCount() <= 0 && channel.isStoped())
            {
                System.out.println("[Thread]: WorkerThread " + this.getName()
                        + " stop!");
                stop();
            }
            else
            {
                IRequest request = channel.takeRequest();
                try
                {
                    request.execute();
                }
                catch (Exception e)
                {
                    System.out.println(e.getMessage());
                }
            }
        }
    }
}

Client方调用方法：

(1) 首先初始化Channel，设定工作线程数。
int workerCount = ......;
channel = new Channel(workerCount);
(2)启动生产线
channel.startWorkers();
(3)放置Request
channel.putRequest(aRequest);
(4)下班了－－停止生产线
channel.stopWorkers();
workers把目前生产线上的Request处理完后，自己Stop掉自己。