线程池总结

package com.example.ivanThreadPoolTest;

import java.util.LinkedList;
import java.util.List;
import java.util.concurrent.ThreadPoolExecutor;

public final class ThreadPool {
// 线程池中默认线程的个数为5
private static int worker_num = 5;
// 工作线程
private WorkThread[] workThreads;

// 任务队列，作为一个缓冲,List线程不安全
private List<Runnable> taskQueue = new LinkedList<Runnable>();

private static ThreadPool threadPool;

// 创建具有默认线程个数的线程池
public ThreadPool() {
this(5);
}
// 创建线程池,worker_num为线程池中工作线程的个数
private ThreadPool(int worker_num) {
ThreadPool.worker_num = worker_num;
workThreads = new WorkThread[worker_num];
for (int i = 0; i < worker_num; i++) {
workThreads[i] = new WorkThread();
workThreads[i].start();// 开启线程池中的线程
}
}

// 单态模式，获得一个默认线程个数的线程池
public static ThreadPool getThreadPool() {
return getThreadPool(ThreadPool.worker_num);
}

// 单态模式，获得一个指定线程个数的线程池,worker_num(>0)为线程池中工作线程的个数
// worker_num<=0创建默认的工作线程个数
public static ThreadPool getThreadPool(int worker_num1) {
if (threadPool == null)
threadPool = new ThreadPool(worker_num1);
return threadPool;
}

// 执行任务,其实只是把任务加入任务队列，什么时候执行有线程池管理器觉定
public void addTask(Runnable task) {
synchronized (taskQueue) {
taskQueue.add(task);
taskQueue.notifyAll();
}
}

// 销毁线程池,该方法保证在所有任务都完成的情况下才销毁所有线程，否则等待任务完成才销毁
public void destroy() {
while (!taskQueue.isEmpty()) {// 如果还有任务没执行完成，就先睡会吧
try {
Thread.sleep(10);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
// 工作线程停止工作，且置为null
for (int i = 0; i < worker_num; i++) {
workThreads[i].stopWorker();
workThreads[i] = null;
}
threadPool = null;
taskQueue.clear();// 清空任务队列
}

/**
* 内部类，工作线程
*/
private class WorkThread extends Thread {
// 该工作线程是否有效，用于结束该工作线程
private boolean isRunning = true;

/*
* 关键所在啊，如果任务队列不空，则取出任务执行，若任务队列空，则等待
*/
@Override
public void run() {
Runnable r = null;
while (isRunning) {// 注意，若线程无效则自然结束run方法，该线程就没用了
synchronized (taskQueue) {
while (isRunning && taskQueue.isEmpty()) {// 队列为空
try {
taskQueue.wait(20);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
if (!taskQueue.isEmpty())
r = taskQueue.remove(0);// 取出任务
}
if (r != null) {
r.run();// 执行任务
}
r = null;
}
}

// 停止工作，让该线程自然执行完run方法，自然结束
public void stopWorker() {
isRunning = false;
}
}
}

package com.example.ivanThreadPoolTest;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;

public class SystemExecutors {

/**
* 创建一个可缓存线程池，如果线程池长度超过处理需要，可灵活回收空闲线程，若无可回收，则新建线程。
*/
public void cachedThreadPool (){
ExecutorService cachedThreadPool = Executors.newCachedThreadPool();
for (int i = 0; i < 10; i++) {
final int index = i;
//          try {
//              Thread.sleep(index * 1000);
//          } catch (InterruptedException e) {
//              e.printStackTrace();
//          }

cachedThreadPool.execute(new Runnable() {

@Override
public void run() {
System.out.println(index);
}
});
}
}
/**
* 创建一个定长线程池，可控制线程最大并发数，超出的线程会在队列中等待
*/
public void newFixedThreadPool(){
ExecutorService fixedThreadPool = Executors.newFixedThreadPool(3);
for (int i = 0; i < 10; i++) {
final int index = i;
fixedThreadPool.execute(new Runnable() {

@Override
public void run() {
try {
System.out.println(index);
Thread.sleep(2000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
});
}
}

/**
* 创建一个定长线程池，支持定时及周期性任务执行。延迟执行示例代码如下
*/
public void newScheduledThreadPool(){
ScheduledExecutorService scheduledThreadPool = Executors.newScheduledThreadPool(5);
scheduledThreadPool.schedule(new Runnable() {

@Override
public void run() {
System.out.println("delay 3 seconds");
}
}, 3, TimeUnit.SECONDS);
}
/**
* 定期执行示例代码如下：
* 表示延迟1秒后每3秒执行一次。
* ScheduledExecutorService比Timer更安全，功能更强大，后面会有一篇单独进行对比。
*/
public void newScheduledThreadPool2(){
ScheduledExecutorService scheduledThreadPool = Executors.newScheduledThreadPool(5);
scheduledThreadPool.scheduleAtFixedRate(new Runnable() {

@Override
public void run() {
System.out.println("delay 1 seconds, and excute every 3 seconds");
}
}, 1, 3, TimeUnit.SECONDS);
}

/**
* 创建一个单线程化的线程池，它只会用唯一的工作线程来执行任务，保证所有任务按照指定顺序(FIFO, LIFO, 优先级)执行
*/
public void newSingleThreadExecutor(){
ExecutorService singleThreadExecutor = Executors.newSingleThreadExecutor();
for (int i = 0; i < 10; i++) {
final int index = i;
singleThreadExecutor.execute(new Runnable() {

@Override
public void run() {
try {
System.out.println(index);
Thread.sleep(2000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
});
}
}
}

package com.example.ivanThreadPoolTest;

public class MainTest {

public static void main(String[] args) {
ThreadPoolTest();
//      new SystemExecutors().cachedThreadPool();
//      new SystemExecutors().newFixedThreadPool();
//      new SystemExecutors().newScheduledThreadPool();
//      new SystemExecutors().newScheduledThreadPool2();
//      new SystemExecutors().newSingleThreadExecutor();
}
public static void ThreadPoolTest(){

ThreadPool pool;
pool = ThreadPool.getThreadPool();
for(int i = 0 ; i <10 ; i++){
final int index = i;
Runnable r = new Runnable() {

@Override
public void run() {
System.out.println(index);
}
};
pool.addTask(r);
}

}
}