简单线程池的实现

最近看了下JAVA线程相关的资料，顺便写了个自己的线程池的实现方式，记录一下。


首先定义一个简单的任务：

/**
 * Task
 * Created on: 2008-9-29 上午10:29:18
 * Description: 
 */
package cn.edu.ccnu.inc.ivan.thread;

/**
 * @author <a href="mailto:[email protected]">Ivan</a>
 */
public interface Task {

	public int getNum();
	public void execute();
}

其次定义工作线程，该线程用于执行任务：

/**
 * WorkThread
 * Created on: 2008-9-29 上午10:30:06
 * Description: 
 */
package cn.edu.ccnu.inc.ivan.thread;

import java.util.Queue;

/**
 * @author <a href="mailto:[email protected]">Ivan</a>
 */
public class WorkThread extends Thread {
	
	/**
	 * 线程关闭的标识位
	 */
	private boolean shutDown = false;
	
	/**
	 * 线程池管理器
	 */
	ThreadPoolManager mgr;
	
	/**
	 * 任务队列
	 */
	private Queue<Task> taskQueue;
	
	public WorkThread(ThreadPoolManager mgr, Queue<Task> taskQueue, String name) {
		super(name);
		this.mgr = mgr;
		this.taskQueue = taskQueue;
	}
	
	public void run() {
		while(!shutDown) {
			Task task;
			// 如果任务队列不为空，则取出一个任务并开始执行，否则线程等等
			if(!taskQueue.isEmpty()) {
				synchronized(taskQueue) {
					task = taskQueue.poll();
				}
				task.execute();
				// 任务执行完毕之后释放线程到空闲线程队列中
				mgr.releaseThread(this);
			} else {
				try {
					synchronized(taskQueue) {
						taskQueue.wait();
					}
				} catch (InterruptedException e) {
					e.printStackTrace();
				}
			}
		}
	}
	
	public void shutDown() {
		this.shutDown = true;
	}
}

最后就是其核心类，线程池管理器：

/**
 * ThreadPoolManager
 * Created on: 2008-9-29 上午10:34:09
 * Description: 
 */
package cn.edu.ccnu.inc.ivan.thread;
import java.util.Queue;
import java.util.concurrent.ConcurrentLinkedQueue;

/**
 * @author <a href="mailto:[email protected]">Ivan</a>
 */
public class ThreadPoolManager {

	public static int DEFAULT_POOL_SIZE = 5;
	public static int POOL_SIZE = 0;
	
	/**
	 * 空闲线程
	 */
	private Queue<WorkThread> idleThread;
	
	/**
	 * 任务队列
	 */
	private Queue<Task> taskQueue;
	
	/**
	 * 线程池大小
	 */
	private int poolSize;
	
	public ThreadPoolManager() {
		this(DEFAULT_POOL_SIZE);
	}
	
	public ThreadPoolManager(int poolSize) {
		if(poolSize < 0) {
			this.poolSize = DEFAULT_POOL_SIZE;
		} else {
			this.poolSize = poolSize;
		}
		idleThread = new ConcurrentLinkedQueue<WorkThread>();
		taskQueue = new ConcurrentLinkedQueue<Task>();
		init();
	}
	
	/**
	 * 初始化线程池，新建 N 个空闲线程
	 *
	 */
	private void init() {
		System.out.println("Start up thread pool...");
		synchronized(taskQueue) {
			for(int i=0; i < poolSize; i++) {
				WorkThread workThread = new WorkThread(this, taskQueue, "Thread " + i);
				idleThread.add(workThread);
				POOL_SIZE++;
				workThread.start();
			}
		}
	}
	
	/**
	 * 关闭线程池，关闭线程池中各个线程
	 * 在调用该方法后，线程并没有马上关闭，而是在线程任务执行完之后关闭
	 *
	 */
	public void shutDown() {
		System.out.println("Shut down all work thread...");
		synchronized(taskQueue) {
			for(WorkThread thread : idleThread) {
				thread.shutDown();
			}
		}
	}
	
	/**
	 * 添加任务并唤醒各因无任务而等待的空闲线程
	 * @param task
	 * @throws Exception
	 */
	public void addTask(Task task) throws Exception {
		synchronized(taskQueue) {
			taskQueue.add(task);
			taskQueue.notifyAll();
		}
	}
	
//	public void schedule() throws Exception {
//		while(!shutDown) {
//			if(!taskQueue.isEmpty()) {
//				WorkThread workThread = getIdleThread();
//				synchronized(workThread) {
//					workThread.notifyAll();
//				}
//			} else {
//				taskQueue.wait();
//			}
//		}
//	}
	
	/**
	 * 获取空闲线程，当线程池内无空闲线程时等待
	 * @return
	 * @throws Exception
	 */
	public WorkThread getIdleThread() throws Exception {
		if(idleThread.isEmpty()) {
			System.out.println("No idle thread in pool, please wait...");
			idleThread.wait();
		}
		synchronized(idleThread) {
			return idleThread.poll();
		}
	}
	
	/**
	 * 释放线程
	 * @param thread
	 */
	public void releaseThread(WorkThread thread) {
		System.out.println("Release the thread [" + thread.getName() + "] to the pool...");
		synchronized(idleThread) {
			idleThread.add(thread);
			idleThread.notifyAll();
		}
	}
}

测试起来就比较简单，为了模拟线程效果，在任务中只是打印一行执行过程，并让线程睡眠一段时间，同样，在所有任务执行完成后，让线程池睡眠一段时间再关闭：

/**
 * SimpleTask
 * Created on: 2008-9-29 上午10:47:07
 * Description: 
 */
package cn.edu.ccnu.inc.ivan.thread;

import edu.ccnu.inc.ivan.util.DateUtils;

/**
 * @author <a href="mailto:[email protected]">Ivan</a>
 */
public class SimpleTask implements Task {

	int num = 0;
	
	public SimpleTask(int num) {
		this.num = num;
	}

	public void execute() {
		try {
			System.out.println("[" + DateUtils.getTimeNow() + "] Task[" + getNum() + "]:I have worked in thread [" + Thread.currentThread().getName() + "]");
			Thread.sleep(Math.round(Math.random() * 1000));
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
	}

	public int getNum() {
		return num;
	}

	public void setNum(int num) {
		this.num = num;
	}
}

/**
 * TestThreadPoolManager
 * Created on: 2008-9-29 上午10:45:35
 * Description: 
 */
package cn.edu.ccnu.inc.ivan.thread;

import junit.framework.TestCase;

/**
 * @author <a href="mailto:[email protected]">Ivan</a>
 */
public class TestThreadPoolManager extends TestCase {

	public void testManager() throws Exception {
		ThreadPoolManager pool = new ThreadPoolManager();
		for(int i = 0; i < 100; i++) {
			pool.addTask(new SimpleTask(i));
		}
		Thread.sleep(1000 * 10);
		pool.shutDown();
	}

}