Java遊戲起步：（一）線程與線程池

任何遊戲都至少需要運行兩個線程,主線程和GUI線程
而線程池是一個管理運行線程的有用工具,下面的代碼示範了一個線程池的實現方法~~
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(ThreadPool.java)
import java.util.LinkedList;

/**
    線程池是一組線程，限制執行任務的線程數
*/
public class ThreadPool extends ThreadGroup {

    private boolean isAlive;
    private LinkedList taskQueue;
    private int threadID;
    private static int threadPoolID;

    /**
        建立新的線程池，numThreads是池中的線程數
    */
    public ThreadPool(int numThreads) {
        super("ThreadPool-" + (threadPoolID++));
        setDaemon(true);

        isAlive = true;

        taskQueue = new LinkedList();
        for (int i=0; i<numThreads; i++) {
            new PooledThread().start();
        }
    }
    /**
        請求新任務。人物在池中下一空閑線程中運行，任務按收到的順序執行
    */
    public synchronized void runTask(Runnable task) {
        if (!isAlive) {
            throw new IllegalStateException();//線程被關則拋出IllegalStateException異常
        }
        if (task != null) {
            taskQueue.add(task);
            notify();
        }

    }

    protected synchronized Runnable getTask()
        throws InterruptedException
    {
        while (taskQueue.size() == 0) {
            if (!isAlive) {
                return null;
            }
            wait();
        }
        return (Runnable)taskQueue.removeFirst();
    }

    /**
        關閉線程池，所有線程停止，不再執行任務
    */
    public synchronized void close() {
        if (isAlive) {
            isAlive = false;
            taskQueue.clear();
            interrupt();
        }
    }

    /**
        關閉線程池並等待所有線程完成，執行等待的任務
    */
    public void join() {
        //告訴等待線程線程池已關
        synchronized (this) {
            isAlive = false;
            notifyAll();
        }

        // 等待所有線程完成
        Thread[] threads = new Thread[activeCount()];
        int count = enumerate(threads);
        for (int i=0; i<count; i++) {
            try {
                threads[i].join();
            }
            catch (InterruptedException ex) { }
        }
    }

    /**
        用於進行任務的線程
    */
    private class PooledThread extends Thread {

        public PooledThread() {
            super(ThreadPool.this,
                "PooledThread-" + (threadID++));
        }

        public void run() {
            while (!isInterrupted()) {

                // 得到任務
                Runnable task = null;
                try {
                    task = getTask();
                }
                catch (InterruptedException ex) { }

                // 若getTask()返回null或中斷，則關閉此線程並返回
                if (task == null) {
                    return;
                }

                // 運行任務，吸收異常
                try {
                    task.run();
                }
                catch (Throwable t) {
                    uncaughtException(this, t);
                }
            }
        }
    }
}
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要測試這個線程池，可以通過下面這個Test程式！
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(ThreadPoolTest.java)
public class ThreadPoolTest {

    public static void main(String[] args) {
        if (args.length != 2) {
            System.out.println("Tests the ThreadPool task.");
            System.out.println(
                "Usage: java ThreadPoolTest numTasks numThreads");
            System.out.println(
                "  numTasks - integer: number of task to run.");
            System.out.println(
                "  numThreads - integer: number of threads " +
                "in the thread pool.");
            return;
        }
        int numTasks = Integer.parseInt(args[0]);
        int numThreads = Integer.parseInt(args[1]);

        // 產生線程池
        ThreadPool threadPool = new ThreadPool(numThreads);

        // 運行任務
        for (int i=0; i<numTasks; i++) {
            threadPool.runTask(createTask(i));
        }

        // 關閉線程池並等待所有任務完成
        threadPool.join();
    }

    /**
        一個簡單的任務(列印ID)
    */
    private static Runnable createTask(final int taskID) {
        return new Runnable() {
            public void run() {
                System.out.println("Task " + taskID + ": start");

                // 增加耗時
                try {
                    Thread.sleep(500);
                }
                catch (InterruptedException ex) { }

                System.out.println("Task " + taskID + ": end");
            }
        };
    }

}
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這樣的線程池可以在許多地方應用！