Java线程池的实现

线程池的作用：

一个线程的周期分为：创建、运行、销毁三个阶段。

处理一个任务时，首先创建一个任务线程，然后执行任务，完了还要销毁线程。而线程只有处于运行状态的时候，才是真的在处理我们交给它的任务，这个阶段才是有效运行时间。

所以，我们希望花在创建和销毁线程的资源越少越好。如果不销毁线程，而这个线程又不能被其他的任务调用，那么就会出现资源的浪费。为了提高效率，减少创建和销毁线程带来时间和空间上的浪费，出现了线程池技术。这种技术是在开始就创建一定量的线程，批量处理一类任务，等待任务的到来。任务执行完毕后，线程又可以执行其他的任务。等不再需要线程的时候，就销毁。这样就省去了频繁创建和销毁线程的麻烦。

1. 线程池类

import java.util.LinkedList;
import java.util.List;

public class MyThreadPool {
    // 线程池中默认线程的个数为5个
    private static int worker_num = 5;
    // 工作的线程
    private WorkThread[] workThreads;
    // 未处理的任务
    private static volatile int finished_task = 0;
    // 任务队列，作为一个缓冲，List线程不安全所以需要在使用的过程中对它进行同步。
    private List<Runnable> taskQueue = new LinkedList<Runnable>();

    // 单例模式
    private static MyThreadPool threadPool;
    // 私有化构造方法
    private MyThreadPool(){
        this(5);
    }
    // 创建线程池，num为线程池工作线程的个数
    private MyThreadPool(int num) {
        MyThreadPool.worker_num = num;
        workThreads = new WorkThread[num];
        for (int i = 0; i < num; i++) {
            workThreads[i] = new WorkThread();
            workThreads[i].start();
        }
    }

    // 获得一个线程池,默认线程数
    public static MyThreadPool getThreadPool(){
        return getThreadPool(MyThreadPool.worker_num);
    }
    // 单例模式，获得一个线程池
    public static MyThreadPool getThreadPool(int num) {
        if(num <= 0){
            num = MyThreadPool.worker_num;
        }
        if(threadPool == null){
            synchronized(MyThreadPool.class){
                if(threadPool == null)
                    threadPool = new MyThreadPool(num);
            }
        }
        return threadPool;
    }

    /**
     * 执行任务
     * 将该任务加入到任务队列的末尾，等待工作线程的调度
     * @param task
     */
    public void execute(Runnable task){
        synchronized (taskQueue){
            taskQueue.add(task);
            taskQueue.notify();
        }
    }

    /**
     * 批量执行任务
     * 将任务放到任务队列的末尾，等待工作线程的调度
     * @param task
     */
    public void execute(Runnable[] task){
        synchronized (taskQueue){
            for (Runnable runnable : task) {
                taskQueue.add(runnable);
            }
            taskQueue.notify();
        }
    }

    /**
     * 批量执行任务
     * 将任务放到任务队列的末尾，等待工作线程的调度
     * @param task
     */
    public void execute(List<Runnable> task){
        synchronized (taskQueue){
            for (Runnable runnable : task) {
                taskQueue.add(runnable);
            }
            taskQueue.notify();
        }
    }

    /**
     * 销毁线程池
     * 在所有任务都完成的情况下才销毁所有线程，否则等待任务队列的任务全部完成才销毁
     */
    public void destroy(){
        while(!taskQueue.isEmpty()){// 如果还有任务没执行完成，就等会再看看
            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 < MyThreadPool.worker_num; i++) {
            workThreads[i].stopWorker();
            workThreads[i] = null;
        }
        threadPool = null;
        taskQueue.clear();
    }

    // 返回工作线程的个数
    public int getWorkThreadNumber() {
        return worker_num;
    }

    // 返回已完成任务的个数
    public int getFinishedTaskNumber(){
        return finished_task;
    }

    // 返回任务队列的长度，即还没处理的任务个数
    public int getWaitTaskNumber(){
        return taskQueue.size();
    }

    // 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 + "  finished task number:"
                + finished_task + "  wait task number:" + getWaitTaskNumber();
    }

    /**
     * 内部类，工作线程用来执行任务线程
     * @author liu
     *
     */
    private class WorkThread extends Thread{
        // 该工作线程是否有效，用于自然结束该工作线程
        private boolean isRunning = true;

        /*
         * 工作线程的关键之处，如果任务队列不空，则取出任务执行，若任务队列空，则等待。直到任务队列有任务时才取出执行
         */
        @Override
        public void run() {
            Runnable r = null;
            while( isRunning ){// 队列为空
                synchronized (taskQueue){
                    while(isRunning && taskQueue.isEmpty()){
                        try {
                            taskQueue.wait(20);
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                    }

                    if(!taskQueue.isEmpty()){
                        // 取出任务
                        r = taskQueue.remove(0);
                    }
                }

                if(r != null){
                    r.run();
                    // 完成的任务加一
                    finished_task += 1;
                }

                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() {
            this.isRunning = false;
        }

    }
}

2. 测试代码

public class TestThreadPool {

    public static void main(String[] args) {
        // 创建5个线程的线程池
        MyThreadPool t = MyThreadPool.getThreadPool(5);
        Runnable[] r = new Runnable[] { new Task(), new Task(), new Task()};
        t.execute(r);
        r = new Runnable[] {new Task(), new Task(), new Task()};
        t.execute(r);
        System.out.println(t);
        t.destroy();// 所有线程都执行完成才destory
        System.out.println(t);
    }

    // 任务类
    static class Task implements Runnable {
        private static volatile int i = 1;

        @Override
        public void run() {// 执行任务
            System.out.println("任务 " + (i++) + " 完成");
        }
    }
}

3. 运行结果

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MAAARxCaf4trjkUan5uOC+Z/X67QQAANiIKpzirqyQPr/NlE/nj7bJRRjrSIQTAACehiyc9R6s+FZ7mijKp/HrqVvrkAsqzzgBAGA/2lu1ngeHbYmqfwJuh61ahBMAAPZm0zNO//dxhF+IPRwOrR+D1fIvChKFE9UEAIA96PDlIOdtKdEVZ5qnsd41XgAAAHTh7xHO4hkn604AANiDrcK55nln1ETFDHFZWbxGOAEAoC+xAxAKKaolra9QaRmmljh3cQEAALrAIe8AAAABEE4AAIAACCcAAEAAhBMAACAAwgkAABAA4QQAAAiAcAIAAARoCKfn7yCdfyt5uwzpH4OuOOPdWRBnBgEAwH7EhLM+kcA4e93iOrYOeFczbxYknigEAADQhdjJQWVix9k9Cq7Tau3ctIONwioOAADgpsMh77+6smrcLoNjwenFbycAAMBGVOEUd2WF9PlttnwmjzkDstlcRyKcAADwNGThrPdgxbfa08T26vN2GULiaVIIKs84AQBgP9pbtZ4HhyskquNubaGUCCcAAOzHpmecW76P4/l2kJZ/UZAonKgmAADsQYcvB615xOj7cxQxT2O9a7wAAADowvOE8zqma8XY+Qce4SyecbLuBACAPdgqnF2edzZMVMwQl5XFa4QTAAD6EjsAoZCiWtL6CpWWYWqJcxcXAACgCxzyDgAAEADhBAAACIBwAgAABEA4AQAAAiCcAAAAARBOAACAAAgnAABAgIZwev4O0vm3kslvik2Ej3h3FsSZQQAAsB8x4axPJDDOXi9Y8XMoYubNgsQThQAAALoQOzmoTOw4u2dmnXB6rq4QVwAAgHV0OOT9V1fWlI4/wFmXbrwFAADoiCqc4q6skD6/rbFVm+D/eZTmOhLhBACApyELZ70HK77Vnia290iv42HFt4MUCkHlGScAAOxHe6vW8+BwhURdx+iPcqoUSolwAgDAfmx6xql8HccjV7fL0BZOLf+iIFE4UU0AANiDDl8OWvGI8XYZQju1aZ7Getd4AQAA0IXnCed1TJaKG/4uRRPO4hkn604AANiDrcLZ5Xlnw0TFDHFZWbxGOAEAoC+xAxAKKaolra9QaRmmljh3cQEAALrAIe8AAAABEE4AAIAACCcAAEAAhBMAACAAwgkAABAA4QQAAAiAcAIAAARoCKfn7yBjfyuZHCAUPePdWRBnBgEAwH7EhLM+kcA4e71i+kXOgFyKmTcLEk8UAgAA6ELs5KAysePsnoXruOWIWuPqCnEFAABYR4dD3n91ZU2J66YXv50AAAAbUYVT3JUV0ue36fJ5uwyH8Zr+RIp3z7a5jkQ4AQDgacjCWe/Bim+1p4mSfE6SuYjldQz/uJhah1xQecYJAAD70d6q9Tw4dEjUdSzWmLfL0Ek5C6VEOAEAYD82PeOMfB+n0knHklPLvyhIFE5UEwAA9qDDl4O8jxgzpbxdhsBfpqR5Gutd4wUAAEAXniicjz/knAjt0nqEs3jGyboTAAD2YKtwrnreGTRRMUNcVhavEU4AAOhL7ACEQopqSesrVFqGqSXOXVwAAIAucMg7AABAAIQTAAAgAMIJAAAQAOEEAAAIgHACAAAEQDgBAAACPE84151NWx1x+zxeVfQLq9yR9HdwqqMW44EQTNXFh69qiH6nOG/i74jDNawL0adAbLwJsnCK58hudJba5Ol5QtVgi3DuSuX7Pp3SOlDxrxTOrm323x0ck9nWK4dlLdjWeYTY6FNe1xFqM7Jwis2z8Zeo200u3YFw7spO/fDlE1KEczvPbcRpCvfeqxiE88FTYyNdxt0uw3toJ8KpgnBuyRXhXM1/dHB8gyo3QDgfPDE2yhq/fnD5/f1Vn3HOjlnMziqQbfGl1bp3gGVpPVdRSp+HgC6cS3G+sh4plX0f9flbfsk3A56sEDeZivBa3t4uw2G8zD64J77fWla5MEKrl+0NZUrfuR8W3isM0TfiDB/a23f5VnPpeTlsft2x4QgA8TlD/UxXNEMzvt1TJD46DvvqpjbvX0rVGkUJtnYra2YQGxtjo2hLd5X3piWcy3b/7TLcq3Qd09rli+e7T+7v09nB7AF1ta0JZ95eyx12WYWF6bs8bOZLxVzGOasyLDSD8nAYLrf5RXIxzzAzyqqX7o3kbjlSxSDfgD0pFPxqtbKeymghI0PDh+sCwLpVDzYj93ZP0Uz41DicxhZjOhNE8G0yuBiNoqc3Po4b87CI2GjGRmLsXYuub7HkVITzoZLXcbhcpmnC4yO5uo+GKAa9PFzFuZWczwO1Xa2yxB/N1kfYbBblSeS10AzKJfznGcoSlLIdZr10z3tZJkkbWSWcWis3PpPL0TM0fLgyAPy31oseMU27pzhM+Kg4nAbUXEa2PhYar1npagsFZmR9hdO4i9jIkt/FMlX0dxbOaX0+Xn/nf2c/CjtfivosTOmuxkRpjXCqfaEinwTVV6r2eCfhXDq/Wq91vdqsy1qeJZy/WWOWW25yhroP1waAeasSbKbx7Z7iMOGj4rBKs/URwnWe7I/jOFxu8ydz7mqjGHXoLJzEhoN6b7bz46WVmMJ5GWeHjddUOO0VpyWcN2Nh01U4lfYpdzg+asVpWtRB9HrN5Z4onHmZ7Q0oK5/uK04j2Kwb2z3FYcJHxaG4TNm+5Jw2Q6/jfb8xmSA3GuUJwklsOClD4T10Uz0A4T5xWEabYZjtzTcS6l3shnBWOUh3pHaEhdMYuaU99zSGin3lbcKZFpY5NBCUWdxYiuRSFuuO0FMTk1cIZx49zkYRLIsHgJ6pFWyG8e2eohn/uXHozt7JdTwM4zjM8/5xzFq20SjW9kbYLmJDs0OsanVHNi69xz7tb0s4i+/85K4Sdxh8wjkPTOrKVcnPKZxLAbWR6YVp00OqVjZJNTEH/cRP05fQHEFZWC6FkXR5VVBm7dhtHidHt7CJ05z2mqkKV/i2aoWEGwOgzrMKcyHYDOPbPUXio+NQdeBaslKK0UtvFCPYthhJbMh2KI6yY+MdVPOXs2oBAABCIJwAAAABEE4AAIAACCcAAEAAhBMAACAAwgkAABAA4QQAAAiAcAIAAARAOAEAAAIgnAAAAAEQTgAAgAAIJwAAQACEEwAAIADCCQAAEADhBAAACIBwAgAABEA4AQAAAiCcAAAAARBOAACAAAgnAABAgP8DBW7AAbA+/rAAAAAASUVORK5CYII=" 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注：参照网上的代码和思路，通过自己的修改和调试完成