任何游戏都至少需要运行两个线程,主线程和GUI线程
而线程池是一个管理运行线程的有用工具,下面的代码示范了一个线程池的实现方法~~
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(ThreadPool.java)
import java.util.LinkedList;
/**
线程池是一组线程，限制执行任务的线程数
*/
public class ThreadPool extends ThreadGroup {
private boolean isAlive;
private LinkedList taskQueue;
private int threadID;
private static int threadPoolID;
/**
创建新的线程池，numThreads是池中的线程数
*/
public ThreadPool(int numThreads) {
super("ThreadPool-" + (threadPoolID++));
setDaemon(true);
isAlive = true;
taskQueue = new LinkedList();
for (int i=0; i<numThreads; i++) {
new PooledThread().start();
}
}
/**
请求新任务。人物在池中下一空闲线程中运行，任务按收到的顺序执行
*/
public synchronized void runTask(Runnable task) {
if (!isAlive) {
throw new IllegalStateException();//线程被关则抛出IllegalStateException异常
}
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();
}
/**
关闭线程池，所有线程停止，不再执行任务
*/
public synchronized void close() {
if (isAlive) {
isAlive = false;
taskQueue.clear();
interrupt();
}
}
/**
关闭线程池并等待所有线程完成，执行等待的任务
*/
public void join() {
//告诉等待线程线程池已关
synchronized (this) {
isAlive = false;
notifyAll();
}
// 等待所有线程完成
Thread[] threads = new Thread[activeCount()];
int count = enumerate(threads);
for (int i=0; i<count; i++) {
try {
threads[i].join();
}
catch (InterruptedException ex) { }
}
}
/**
用于进行任务的线程
*/
private class PooledThread extends Thread {
public PooledThread() {
super(ThreadPool.this,
"PooledThread-" + (threadID++));
}
public void run() {
while (!isInterrupted()) {
// 得到任务
Runnable task = null;
try {
task = getTask();
}
catch (InterruptedException ex) { }
// 若getTask()返回null或中断，则关闭此线程并返回
if (task == null) {
return;
}
// 运行任务，吸收异常
try {
task.run();
}
catch (Throwable t) {
uncaughtException(this, t);
}
}
}
}
}
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要测试这个线程池，可以通过下面这个Test程序！
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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]);
// 生成线程池
ThreadPool threadPool = new ThreadPool(numThreads);
// 运行任务
for (int i=0; i<numTasks; i++) {
threadPool.runTask(createTask(i));
}
// 关闭线程池并等待所有任务完成
threadPool.join();
}
/**
一个简单的任务(打印ID)
*/
private static Runnable createTask(final int taskID) {
return new Runnable() {
public void run() {
System.out.println("Task " + taskID + ": start");
// 增加耗时
try {
Thread.sleep(500);
}
catch (InterruptedException ex) { }
System.out.println("Task " + taskID + ": end");
}
};
}
}
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这样的线程池可以在许多地方应用！ 
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