参考《Java并发编程的艺术》
接口
package pres.ndz.simple.thread;
import org.quartz.Job;
public interface ThreadPool<Job extends Runnable> {
void execute(Job job);
void shutdowm();
void addWorkers(int num);
void removeWorker(int num);
int getJobSize();
}
实现
package pres.ndz.simple.thread;
import java.util.ArrayList;
import java.util.Collections;
import java.util.LinkedList;
import java.util.List;
import java.util.concurrent.atomic.AtomicLong;
/**
* 实现默认线程池
* 线程池中的线程不是由调用方来创建，而是初始化线程池时已经默认创建好了活跃线程，用的时候
* 线程池会自动取线程执行（活跃线程一直在等待执行其实，很像spring）
*/
public class DefaultThreadPool<Job extends Runnable> implements ThreadPool<Job> {
// 线程池最大线程数量
private static final int MAX_WORKER_NUMBERS = 10;
// 默认线程池数量
private static final int DEFAULT_WORKER_NUMBERS = 5;
// 线程池最小线程数量
private static final int MIN_WORKER_NUMBERS = 1;
// 工作清单
private final LinkedList<Job> jobs = new LinkedList<>();
// 工作者列表
private final List<Worker> workers = Collections.synchronizedList(new ArrayList<Worker>());
// 工作者线程数量
private int workerNum = DEFAULT_WORKER_NUMBERS;
// 线程编号生成
private AtomicLong threadNum = new AtomicLong();
public DefaultThreadPool(){
initializeWorkers(DEFAULT_WORKER_NUMBERS);
}
/**
* 指定线程池大小，最大不能超过 MAX_WORKER_NUMBERS
* 最小不能小于 MIN_WORKER_NUMBERS（0或负都将返回 MIN_WORKER_NUMBERS）
*/
public DefaultThreadPool(int num){
workerNum = num > MAX_WORKER_NUMBERS?MAX_WORKER_NUMBERS:num < MIN_WORKER_NUMBERS?
MIN_WORKER_NUMBERS : num;
initializeWorkers(num);
}
/**
* 初始化线程工作者
* 初始完毕后会生成给定数量的Thread 一直查看jobs的数量 ，大于0就执行
*/
private void initializeWorkers(int num){
for (int i = 0; i< num; i++){
Worker worker = new Worker();
workers.add(worker);
Thread thread = new Thread(worker, "ThreadPool-Worker-" + threadNum.incrementAndGet());
thread.start();
}
}
/**
* 调用方执行一个Job
*/
@Override
public void execute(Job job) {
if (job != null) {
// 添加一个工作，然后进行通知
// 多线程环境下添加job，会有资源竞争抢锁问题，所以使用synchronized用来同步添加
synchronized (jobs){
jobs.addLast(job);
// 当前线程添加完毕后，通知其他线程可以添加了
jobs.notify();
}
}
}
/**
* 停止所有的Worker(线程池全部关闭)
*/
@Override
public void shutdowm() {
for (Worker worker : workers){
worker.shutdown();
}
}
/**
* 添加给定数量的Worker
*/
@Override
public void addWorkers(int num) {
synchronized (jobs){
// 限制新增的worker不能超过最大值
if (num + this.workerNum > MAX_WORKER_NUMBERS){
num = MAX_WORKER_NUMBERS - this.workerNum;
}
initializeWorkers(num);
this.workerNum += num;
}
}
/**
* 移除（停止）给定数量停止Worker（线程池数量递减）
*/
@Override
public void removeWorker(int num) {
synchronized (jobs){
if (num >= this.workerNum){
throw new IllegalStateException("beyond workNum");
}
int count = 0;
while (count < num){
Worker worker = workers.get(count);
if (workers.remove(worker)){
worker.shutdown();
count ++;
}
}
}
}
@Override
public int getJobSize() {
return jobs.size();
}
/**
* 工作者（任务），负责消费任务
*/
class Worker implements Runnable{
// 是否工作
private volatile boolean running = true;
@Override
public void run() {
while (running){
Job job = null;
synchronized (jobs){
while (jobs.isEmpty()){
try {
jobs.wait();
}catch (InterruptedException ex){
// 感知到外部对WorkerThread的中断操作，返回
Thread.currentThread().interrupt();
return;
}
}
// 从工作清单中取出一个Job
job = jobs.removeFirst();
}
if(job != null ){
try {
job.run();
}catch (Exception ex){
// 忽略Job执行中的异常
}
}
}
}
public void shutdown(){
running = false;
}
}
}
测试
public class GarbageTest {
@Test
public void test() throws InterruptedException {
ThreadPool pool = new DefaultThreadPool(2);
for (int i = 0; i < 10; i++) {
if(i == 5) pool.removeWorker(1);
pool.execute(()-> {
System.out.printf("Thread is [%s], Job start ....
",Thread.currentThread().getName());
try {
Thread.sleep(2*1000);
} catch (InterruptedException e) {
e.printStackTrace();
}
});
}
Thread.sleep(60*10000);
}
}
结果
Thread is [ThreadPool-Worker-1], Job start ....
Thread is [ThreadPool-Worker-2], Job start ....
Thread is [ThreadPool-Worker-2], Job start ....
Thread is [ThreadPool-Worker-2], Job start ....
Thread is [ThreadPool-Worker-2], Job start ....
Thread is [ThreadPool-Worker-2], Job start ....
Thread is [ThreadPool-Worker-2], Job start ....
Thread is [ThreadPool-Worker-2], Job start ....
Thread is [ThreadPool-Worker-2], Job start ....
Thread is [ThreadPool-Worker-2], Job start ....
Process finished with exit code 130 (interrupted by signal 2: SIGINT)