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背景：2019年4月春招找实习，面试华为后端开发，面试官上来给了一张A4纸，让手写一个java线程池，要求可运行。

============================ 分割线 ================================

一、首先回顾一下线程池的原理

根据以上流程图，编写线程池代码

package scu.stone.thread;import java.util.concurrent.ArrayBlockingQueue;import java.util.concurrent.BlockingQueue;public class MyThreadPool {
   	//线程池中默认线程的个数为5	private static int WORK_NUM = 5;	//队列默认任务为100	private static int TASK_COUNT = 100;		//工作线程数组	private WorkThread[] workThreads;	//等待队列	private final BlockingQueue
   
     taskQueue;	//用户在构造这个线程池时，希望启动的线程数	private final int workerNum;  		/**	 * 内部类，工作线程类	 */	private class WorkThread extends Thread{
   		@Override		public void run() {
   			Runnable runnable = null;			try {
   				while (! isInterrupted()) {
     //如果没有被标记中断，则从对阻塞队列中取出任务执行					runnable = taskQueue.take();  //take：阻塞接口的移除方法					if (runnable != null) {
   						System.out.println("Thread ID:" + getId() + " ready exec:" + runnable.toString());						runnable.run();					}					runnable = null;  //help gc 				}			} catch (Exception e) {
   				// TODO: handle exception			}		}		//线程停止工作		public void stopWork() {
   			interrupt();		}	}		//构造方法：创建具有默认线程个数的线程池	public MyThreadPool() {
   		this(WORK_NUM,TASK_COUNT);	}	//创建线程池,workNum为线程池中工作线程的个数	public MyThreadPool(int workerNum, int taskCount) {
   		if (workerNum <= 0) {
   			workerNum = WORK_NUM;		}		if (taskCount <= 0) {
   			taskCount = TASK_COUNT;		}		this.workerNum = workerNum;		taskQueue = new ArrayBlockingQueue<>(taskCount);		workThreads = new WorkThread[workerNum];		for (int i = 0; i < workerNum; i++) {
   			workThreads[i] = new WorkThread();  //new一个工作线程			workThreads[i].start();  //启动工作线程		}		Runtime.getRuntime().availableProcessors();	}	//执行任务，其实就是把任务加入任务队列，什么时候执行由线程池管理器决定	public void execute(Runnable task) {
   		try {
   			taskQueue.put(task);   //put:阻塞接口的插入		} catch (Exception e) {
   			// TODO: handle exception		}	}	//销毁线程池,该方法保证所有任务都完成的情况下才销毁所有线程，否则等待任务完成再销毁	public void destory() {
   		//工作线程停止工作，且置为null		System.out.println("ready close thread...");		for (int i = 0; i < workerNum; i++) {
   			workThreads[i].stopWork();			workThreads[i] = null; //help gc		}		taskQueue.clear();  //清空等待队列			}	//覆盖toString方法，返回线程信息：工作线程个数和已完成任务个数	@Override	public String toString() {
   		return "WorkThread number:" + workerNum + " ==分割线== wait task number:" + taskQueue.size();	}}
   

2.任务类

package scu.stone.thread;import java.util.Random;public class MyTask implements Runnable {
   		private String name;	public String getName() {
   		return name;	}	private Random random = new Random();		public MyTask(String name) {
   		this.name = name;	}	@Override	public void run() {
   		try {
   			Thread.sleep(random.nextInt(1000) + 2000);		} catch (Exception e) {
   			System.out.println(Thread.currentThread().getId() + "sleep InterruptedException:" + 					Thread.currentThread().isInterrupted());		}		System.out.println("task--- " + name + "---done!");	}}

3.测试类

package scu.stone.thread;import java.util.concurrent.BlockingQueue;import java.util.concurrent.RejectedExecutionHandler;import java.util.concurrent.ThreadPoolExecutor;import java.util.concurrent.TimeUnit;public class TestMyThreadPool extends ThreadPoolExecutor{
   	public TestMyThreadPool(int corePoolSize,int maximumPoolSize,long keepAliveTime,TimeUnit unit,			BlockingQueue
   
     workQueue,RejectedExecutionHandler handler) {
   		super(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue, handler);	}		public static void main(String[] args) throws InterruptedException {
   		//创建3个线程的线程池		MyThreadPool myThreadPool = new MyThreadPool(3, 3);		myThreadPool.execute(new MyTask("A"));		myThreadPool.execute(new MyTask("B"));		myThreadPool.execute(new MyTask("C"));		myThreadPool.execute(new MyTask("D"));		myThreadPool.execute(new MyTask("E"));				System.out.println(myThreadPool);		Thread.sleep(10000);		myThreadPool.destory(); //所有线程都执行完成后，再destory		System.out.println(myThreadPool);	}}
   

4.测试结果，如下：

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