文章目录

• 概述
• 示例

概述

我们工作中，并发编程必然离不开jdk提供的j.u.c中的线程池 ，假设让我们自己去设计一个线程池，该从哪几个方面来着手考虑呢？

首先： 既然是线程池 ， 那必然 有个初始化的线程数量 和 最大数量 ----> 两个属性 ： init 和 max

其次：当线程池中的线程达到了 init 数量，但还没到max 数量的时候，将任务放入任务队列中，而不是直接开辟新的线程，是不是一种更好的设计？ 所以 引入 任务队列，存放任务

最后：当线程池中的线程 把 任务队列也塞满了，也达到了Max的值，新的线程过来，我们改如何处理呢？ 是不是指定拒绝策略更合适呢？ 比如 直接拒绝，抛出异常，放入临时队列等等。所以 拒绝策略也是需要的

总结一下

init （coreSize） / max , 线程池初始化大小和最大线程数

任务队列

拒绝策略

。。。

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示例

逐步实现该需求， 先把基本的流程调通，这里我们先实现定义线程池数量的功能 ，代码如下

package com.artisan.test;import java.util.ArrayList; import java.util.LinkedList; import java.util.List; import java.util.stream.IntStream;public class SimpleThreadPool {// 线程数private int size;// 默认线程数private static int DEFAULT_SIZE = 10;// 任务队列private final static LinkedList<Runnable> TASK_QUEUE = new LinkedList();// 工作线程集合private final static List<WorkTask> THREAD_QUEUE = new ArrayList<>();private static volatile int seq = 0;private static final ThreadGroup GROUP = new ThreadGroup("Pool_Group");private static final String THREAD_PREFIX = "SIMPLE_THREAD_POOL-";/*** 默认构造函数* 默认10个线程*/public SimpleThreadPool() {this(DEFAULT_SIZE);}/*** 线程池中的线程数量** @param size*/public SimpleThreadPool(int size) {this.size = size;// 初始化init();}/*** 初始化*/private void init() {for (int i = 0; i < size; i++) {createWorkTask();}}/*** 创建工作线程*/private void createWorkTask() {// 创建工作线程WorkTask workTask = new WorkTask(GROUP, THREAD_PREFIX + (seq++));// 启动workTask.start();// 加入到工作线程集合THREAD_QUEUE.add(workTask);}/*** 将任务runnable 提交到 TASK_QUEUE** @param runnable*/public void submit(Runnable runnable) {synchronized (TASK_QUEUE) {// 添加到队列的最后面TASK_QUEUE.addLast(runnable);// 唤醒所有正在等待的线程TASK_QUEUE.notifyAll();}}/*** 线程状态*/enum TaskState {FREE,RUNNING,BLOCKED,DEAD}/*** private 私有类* 继承Thread 的 工作线程*/private static class WorkTask extends Thread {// 默认状态 FREEprivate volatile TaskState state = TaskState.FREE;public WorkTask(ThreadGroup threadGroup, String name) {super(threadGroup, name);}/*** 获取线程状态** @return*/public TaskState getTaskState() {return this.state;}/*** 重写run方法*/@Overridepublic void run() {// 跳出while的标识OUTER:// 只要不是DEAD 状态，一直从队列中获取消息while (state != TaskState.DEAD) {Runnable runnable;// 对队列进行加锁操作synchronized (TASK_QUEUE) {// 如果队列为空，waitwhile (TASK_QUEUE.isEmpty()) {try {// 更改状态state = TaskState.BLOCKED;// wait 放弃该锁TASK_QUEUE.wait();} catch (InterruptedException e) {// 如果有个线程在wait,终止该线程会被InterruptedException异常捕获，// break OUTER 跳出while循环，从而达到终止这个线程break OUTER;}}// TASK_QUEUE不为空 从队列中获取一个Runnable对象// Removes and returns the first element from this listrunnable = TASK_QUEUE.removeFirst();}if (runnable != null) {// 运行状态state = TaskState.RUNNING;// 运行runnable.run();// 运行结束后 置为FREEstate = TaskState.FREE;}}}/*** 关闭线程*/public void close() {this.state = TaskState.DEAD;}}/*** 测试** @param args*/public static void main(String[] args) {SimpleThreadPool simpleThreadPool = new SimpleThreadPool(); // for (int i = 0; i < 50; i++) { // simpleThreadPool.submit(()->{ // try { // System.out.println(Thread.currentThread().getName() + " is running" ); // Thread.sleep(1_000); // System.out.println(Thread.currentThread().getName() + " finished" ); // } catch (InterruptedException e) { // e.printStackTrace(); // } // }); // }IntStream.range(0, 50).forEach(i ->simpleThreadPool.submit(() -> {try {System.out.println(Thread.currentThread().getName() + "____" + i + " start");Thread.sleep(1_000);System.out.println(Thread.currentThread().getName() + "____" + i +" finished");} catch (InterruptedException e) {e.printStackTrace();}}));} }

运行：

SIMPLE_THREAD_POOL-9____0 start SIMPLE_THREAD_POOL-4____5 start SIMPLE_THREAD_POOL-0____9 start SIMPLE_THREAD_POOL-5____4 start SIMPLE_THREAD_POOL-6____3 start SIMPLE_THREAD_POOL-8____1 start SIMPLE_THREAD_POOL-7____2 start SIMPLE_THREAD_POOL-1____8 start SIMPLE_THREAD_POOL-3____6 start SIMPLE_THREAD_POOL-2____7 start SIMPLE_THREAD_POOL-4____5 finished SIMPLE_THREAD_POOL-6____3 finished SIMPLE_THREAD_POOL-5____4 finished SIMPLE_THREAD_POOL-3____6 finished SIMPLE_THREAD_POOL-0____9 finished SIMPLE_THREAD_POOL-9____0 finished SIMPLE_THREAD_POOL-0____13 start SIMPLE_THREAD_POOL-2____7 finished SIMPLE_THREAD_POOL-5____12 start SIMPLE_THREAD_POOL-1____8 finished SIMPLE_THREAD_POOL-6____11 start SIMPLE_THREAD_POOL-7____2 finished SIMPLE_THREAD_POOL-4____10 start SIMPLE_THREAD_POOL-8____1 finished SIMPLE_THREAD_POOL-7____17 start SIMPLE_THREAD_POOL-1____16 start SIMPLE_THREAD_POOL-2____15 start SIMPLE_THREAD_POOL-9____14 start SIMPLE_THREAD_POOL-8____18 start SIMPLE_THREAD_POOL-3____19 start SIMPLE_THREAD_POOL-0____13 finished SIMPLE_THREAD_POOL-0____20 start SIMPLE_THREAD_POOL-5____12 finished SIMPLE_THREAD_POOL-5____21 start SIMPLE_THREAD_POOL-6____11 finished SIMPLE_THREAD_POOL-6____22 start SIMPLE_THREAD_POOL-4____10 finished SIMPLE_THREAD_POOL-4____23 start SIMPLE_THREAD_POOL-7____17 finished SIMPLE_THREAD_POOL-7____24 start SIMPLE_THREAD_POOL-1____16 finished SIMPLE_THREAD_POOL-1____25 start SIMPLE_THREAD_POOL-2____15 finished SIMPLE_THREAD_POOL-2____26 start SIMPLE_THREAD_POOL-9____14 finished SIMPLE_THREAD_POOL-9____27 start SIMPLE_THREAD_POOL-8____18 finished SIMPLE_THREAD_POOL-8____28 start SIMPLE_THREAD_POOL-3____19 finished SIMPLE_THREAD_POOL-3____29 start SIMPLE_THREAD_POOL-5____21 finished SIMPLE_THREAD_POOL-2____26 finished SIMPLE_THREAD_POOL-1____25 finished SIMPLE_THREAD_POOL-7____24 finished SIMPLE_THREAD_POOL-4____23 finished SIMPLE_THREAD_POOL-0____20 finished SIMPLE_THREAD_POOL-6____22 finished SIMPLE_THREAD_POOL-0____35 start SIMPLE_THREAD_POOL-4____34 start SIMPLE_THREAD_POOL-7____33 start SIMPLE_THREAD_POOL-1____32 start SIMPLE_THREAD_POOL-8____28 finished SIMPLE_THREAD_POOL-3____29 finished SIMPLE_THREAD_POOL-2____31 start SIMPLE_THREAD_POOL-9____27 finished SIMPLE_THREAD_POOL-5____30 start SIMPLE_THREAD_POOL-9____39 start SIMPLE_THREAD_POOL-3____38 start SIMPLE_THREAD_POOL-8____37 start SIMPLE_THREAD_POOL-6____36 start SIMPLE_THREAD_POOL-8____37 finished SIMPLE_THREAD_POOL-2____31 finished SIMPLE_THREAD_POOL-5____30 finished SIMPLE_THREAD_POOL-3____38 finished SIMPLE_THREAD_POOL-9____39 finished SIMPLE_THREAD_POOL-6____36 finished SIMPLE_THREAD_POOL-9____44 start SIMPLE_THREAD_POOL-0____35 finished SIMPLE_THREAD_POOL-4____34 finished SIMPLE_THREAD_POOL-3____43 start SIMPLE_THREAD_POOL-4____47 start SIMPLE_THREAD_POOL-7____33 finished SIMPLE_THREAD_POOL-7____48 start SIMPLE_THREAD_POOL-5____42 start SIMPLE_THREAD_POOL-1____32 finished SIMPLE_THREAD_POOL-2____41 start SIMPLE_THREAD_POOL-8____40 start SIMPLE_THREAD_POOL-1____49 start SIMPLE_THREAD_POOL-0____46 start SIMPLE_THREAD_POOL-6____45 start SIMPLE_THREAD_POOL-3____43 finished SIMPLE_THREAD_POOL-5____42 finished SIMPLE_THREAD_POOL-7____48 finished SIMPLE_THREAD_POOL-4____47 finished SIMPLE_THREAD_POOL-9____44 finished SIMPLE_THREAD_POOL-6____45 finished SIMPLE_THREAD_POOL-0____46 finished SIMPLE_THREAD_POOL-1____49 finished SIMPLE_THREAD_POOL-8____40 finished SIMPLE_THREAD_POOL-2____41 finished

可知： 虽然定义了50个任务，但是根据日志来看，是由10个线程来完成的，符合预期。

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