Java自定义线程池和线程总数控制

1 概述

池化是常见的思想，线程池是非常典型的池化的实现，《Java并发编程实战》也大篇幅去讲解了Java中的线程池。本文实现一个简单的线程池。

2 核心类

【1】接口定义

public interface IThreadPool<Job extends Runnable> {/** * 关闭线程池 */public void shutAlldown();/** * 执行任务 *  * @param job 任务 */public void execute(Job job);/** * 添加工作者 *  * @param addNum 添加数 */public void addWorkers(int addNum);/** * 减少工作者 *  * @param reduceNum 减少数目 */public void reduceWorkers(int reduceNum);}

【2】实现类

线程池的核心是维护了1个任务列表和1个工作者列表。

import java.util.ArrayList;import java.util.Collections;import java.util.LinkedList;import java.util.List;public class XYThreadPool<Job extends Runnable> implements IThreadPool<Job> {// 默认线程数private static int DEAFAULT_SIZE = 5;// 最大线程数private static int MAX_SIZE = 10;// 任务列表private LinkedList<Job> tasks = new LinkedList<Job>();// 工作线程列表private List<Worker> workers = Collections.synchronizedList(new ArrayList<Worker>());/** * 默认构造函数 */public XYThreadPool() {initWokers(DEAFAULT_SIZE);}/** * 执行线程数 *  * @param threadNums 线程数 */public XYThreadPool(int workerNum) {workerNum = workerNum <= 0 ? DEAFAULT_SIZE: workerNum > MAX_SIZE ? MAX_SIZE : workerNum;initWokers(workerNum);}/** * 初始化线程池 *  * @param threadNums 线程数 */public void initWokers(int threadNums) {for (int i = 0; i < threadNums; i++) {Worker worker = new Worker();worker.start();workers.add(worker);}// 添加关闭钩子Runtime.getRuntime().addShutdownHook(new Thread() {public void run() {shutAlldown();}});}@Overridepublic void shutAlldown() {for (Worker worker : workers) {worker.shutdown();}}@Overridepublic void execute(Job job) {synchronized (tasks) {// 提交任务就是将任务对象加入任务队列，等待工作线程去处理tasks.addLast(job);tasks.notifyAll();}}@Overridepublic void addWorkers(int addNum) {// 新线程数必须大于零，并且线程总数不能大于最大线程数if ((workers.size() + addNum) <= MAX_SIZE && addNum > 0) {initWokers(addNum);} else {System.out.println("addNum too large");}}@Overridepublic void reduceWorkers(int reduceNum) {if ((workers.size() - reduceNum <= 0))System.out.println("thread num too small");else {// 暂停指定数量的工作者int count = 0;while (count != reduceNum) {for (Worker w : workers) {w.shutdown();count++;}}}}/** * 工作线程 */class Worker extends Thread {private volatile boolean flag = true;@Overridepublic void run() {while (flag) {Job job = null;// 加锁（若只有一个woker可不必加锁，那就是所谓的单线程的线程池，线程安全）synchronized (tasks) {// 任务队列为空while (tasks.isEmpty()) {try {// 阻塞，放弃对象锁，等待被notify唤醒tasks.wait();System.out.println("block when tasks is empty");} catch (InterruptedException e) {e.printStackTrace();}}// 不为空取出任务job = tasks.removeFirst();System.out.println("get job:" + job + ",do biz");job.run();}}}public void shutdown() {flag = false;}}}

1 当调用wait()方法时线程会放弃对象锁，进入等待此对象的等待锁定池，只有针对此对象调用notify()方法后本线程才进入对象锁定池准备

2 Object的方法：void notify(): 唤醒一个正在等待该对象的线程。void notifyAll(): 唤醒所有正在等待该对象的线程。notifyAll使所有原来在该对象上等待被notify的线程统统退出wait状态，变成等待该对象上的锁，一旦该对象被解锁，它们会去竞争。notify只是选择一个wait状态线程进行通知，并使它获得该对象上的锁，但不惊动其它同样在等待被该对象notify的线程们，当第一个线程运行完毕以后释放对象上的锁，此时如果该对象没有再次使用notify语句，即便该对象已经空闲，其他wait状态等待的线程由于没有得到该对象的通知，继续处在wait状态，直到这个对象发出一个notify或notifyAll，它们等待的是被notify或notifyAll，而不是锁。

3 无需控制线程总数
每调用一次就会创建一个拥有10个线程工作者的线程池。

public class TestService1 {public static void main(String[] args) {// 启动10个线程XYThreadPool<Runnable> pool = new XYThreadPool<Runnable>(10);pool.execute(new Runnable() {@Overridepublic void run() {System.out.println("====1 test====");}});}}public class TestService2 {public static void main(String[] args) {// 启动10个线程XYThreadPool<Runnable> pool = new XYThreadPool<Runnable>(10);pool.execute(new Runnable() {@Overridepublic void run() {System.out.println("====2 test====");}});}}

4 控制线程总数
希望在项目中所有的线程调用，都共用1个固定工作者数大小的线程池。

import javax.annotation.PostConstruct;import org.springframework.stereotype.Component;import com.xy.pool.XYThreadPool;/** * 统一线程池管理类  */@Componentpublic class XYThreadManager {private XYThreadPool<Runnable> executorPool;@PostConstructpublic void init() {executorPool = new XYThreadPool<Runnable>(10);}public XYThreadPool<Runnable> getExecutorPool() {return executorPool;}}import org.springframework.beans.factory.annotation.Autowired;import org.springframework.stereotype.Service;@Service("testService3")public class TestService3 {@Autowiredprivate XYThreadManager threadManager;public void test() {threadManager.getExecutorPool().execute(new Runnable() {@Overridepublic void run() {System.out.println("====3 test====");}});}}import org.springframework.beans.factory.annotation.Autowired;import org.springframework.stereotype.Service;@Service("testService4")public class TestService4 {@Autowiredprivate XYThreadManager threadManager;public void test() {threadManager.getExecutorPool().execute(new Runnable() {@Overridepublic void run() {System.out.println("====4 test====");}});}}import org.springframework.context.ApplicationContext;import org.springframework.context.support.ClassPathXmlApplicationContext;public class TestMain {@SuppressWarnings("resource")public static void main(String[] args) {ApplicationContext atc = new ClassPathXmlApplicationContext("applicationContext.xml");TestService3 t3 = (TestService3) atc.getBean("testService3");t3.test();TestService4 t4 = (TestService4) atc.getBean("testService4");t4.test();}}