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java并发编程(十八)-通过阻塞队列实现一个自己的线程池


什么是线程池?为什么要用线程池?  

  1. 降低资源的消耗。降低线程创建和销毁的资源消耗;
  2. 提高响应速度:线程的创建时间为T1,执行时间T2,销毁时间T3,免去T1和T3的时间
  3. 提高线程的可管理性。

实现一个我们自己的线程池

  1. 线程必须在池子已经创建好了,并且可以保持住,要有容器保存多个线程;

     2、线程还要能够接受外部的任务,运行这个任务。容器保持这个来不及运行的任务.

 

package com.caojiulu.mypool;

import java.util.LinkedList;
import java.util.List;
import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.BlockingQueue;

/**
*@author caojiulu
*
*类说明:自己线程池的实现
*/
public class MyThreadPool {
// 线程池中默认线程的个数为5
private static int WORK_NUM = 5;
// 队列默认任务个数为100
private static int TASK_COUNT = 100;

// 工作线程组
private WorkThread[] workThreads;

// 任务队列,作为一个缓冲
private final BlockingQueue<Runnable> taskQueue;
private final int worker_num;//用户在构造这个池,希望的启动的线程数

// 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,worker_num为线程池中工作线程的个数
public MyThreadPool(int worker_num,int taskCount) {
if (worker_num<=0) worker_num = WORK_NUM;
if(taskCount<=0) taskCount = TASK_COUNT;
this.worker_num = worker_num;
taskQueue = new ArrayBlockingQueue<>(taskCount);
workThreads = new WorkThread[worker_num];
for(int i=0;i<worker_num;i++) {
workThreads[i] = new WorkThread();
workThreads[i].start();
}
Runtime.getRuntime().availableProcessors();
}


// 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决定
public void execute(Runnable task) {
try {
taskQueue.put(task);
} catch (InterruptedException e) {
e.printStackTrace();
}

}


// 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() {
// 工作线程停止工作,且置为null
System.out.println("ready close pool.....");
for(int i=0;i<worker_num;i++) {
workThreads[i].stopWorker();
workThreads[i] = null;//help gc
}
taskQueue.clear();// 清空任务队列
}

// 覆盖toString方法,返回线程池信息:工作线程个数和已完成任务个数
@Override
public String toString() {
return "WorkThread number:" + worker_num
+ " wait task number:" + taskQueue.size();
}

/**
* 内部类,工作线程
*/
private class WorkThread extends Thread{

@Override
public void run(){
Runnable r = null;
try {
while (!isInterrupted()) {
r = taskQueue.take();
if(r!=null) {
System.out.println(getId()+" ready exec :"+r);
r.run();
}
r = null;//help gc;
}
} catch (Exception e) {
// TODO: handle exception
}
}

public void stopWorker() {
interrupt();
}

}
}

测试类:

package com.caojiulu.mypool;

import java.util.Random;

/**
*@author caojiulu
*
*类说明:
*/
public class TestMyThreadPool {
public static void main(String[] args) throws InterruptedException {
// 创建3个线程的线程池
MyThreadPool2 t = new MyThreadPool2(3,0);
t.execute(new MyTask("testA"));
t.execute(new MyTask("testB"));
t.execute(new MyTask("testC"));
t.execute(new MyTask("testD"));
t.execute(new MyTask("testE"));
System.out.println(t);
Thread.sleep(10000);
t.destroy();// 所有线程都执行完成才destory
System.out.println(t);
}

// 任务类
static class MyTask implements Runnable {

private String name;
private Random r = new Random();

public MyTask(String name) {
this.name = name;
}

public String getName() {
return name;
}

@Override
public void run() {// 执行任务
try {
Thread.sleep(r.nextInt(1000)+2000);
} catch (InterruptedException e) {
System.out.println(Thread.currentThread().getId()+" sleep InterruptedException:"
+Thread.currentThread().isInterrupted());
}
System.out.println("任务 " + name + " 完成");
}
}
}

 

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