Java一个简单的线程池实现，java线程池,线程池代码import

Java一个简单的线程池实现，java线程池,线程池代码import

线程池代码

import java.util.List;import java.util.Vector;public class ThreadPool {    private static ThreadPool instance_ = null;    //定义优先级别常数，空闲的线程按照优先级不同分别存放在三个vector中    public static final int LOW_PRIORITY = 0;     public static final int NORMAL_PRIORITY = 1;    public static final int HIGH_PRIORITY = 2;    //保存空闲线程的List，或者说它是"池"    private List<PooledThread>[] idleThreads_;      private boolean shutDown_ = false;    private int threadCreationCounter_; //以创建的线程的个数    private boolean debug_ = false;    //是否输出调试信息    //构造函数，因为这个类视作为singleton实现的，因此构造函数为私有    private ThreadPool()     {               // 产生空闲线程.三个vector分别存放分别处在三个优先级的线程的引用        List[] idleThreads = {new Vector(5), new Vector(5), new Vector(5)};        idleThreads_ = idleThreads;        threadCreationCounter_ = 0;    }    public int getCreatedThreadsCount() {        return threadCreationCounter_;    }    //通过这个函数得到线程池类的实例    public static ThreadPool instance() {        if (instance_ == null)            instance_ = new ThreadPool();        return instance_;    }    public boolean isDebug() {        return debug_;    }    //将线程repoolingThread从新放回到池中，这个方式是同步方法。    //这个方法会在多线程的环境中调用，设计这个方法的目的是让工作者线程    //在执行完target中的任务后，调用池类的repool()方法，    //将线程自身从新放回到池中。只所以这么做是因为线程池并不能预见到    //工作者线程何时会完成任务。参考PooledThread的相关代码。    protected synchronized void repool(PooledThread repoolingThread)    {        if (!shutDown_)         {            if (debug_)            {                System.out.println("ThreadPool.repool() : repooling ");            }            switch (repoolingThread.getPriority())            {                case Thread.MIN_PRIORITY :                {                    idleThreads_[LOW_PRIORITY].add(repoolingThread);                    break;                }                case Thread.NORM_PRIORITY :                {                    idleThreads_[NORMAL_PRIORITY].add(repoolingThread);                    break;                }                case Thread.MAX_PRIORITY :                {                    idleThreads_[HIGH_PRIORITY].add(repoolingThread);                    break;                }                default :                    throw new IllegalStateException("Illegal priority found while repooling a Thread!");            }            notifyAll();//通知所有的线程        }        else         {            if (debug_)            {                System.out.println("ThreadPool.repool() : Destroying incoming thread.");            }            repoolingThread.shutDown();//关闭线程        }        if (debug_)         {            System.out.println("ThreadPool.recycle() : done.");        }    }    public void setDebug(boolean newDebug)     {        debug_ = newDebug;    }    //停止池中所有线程    public synchronized void shutdown()    {        shutDown_ = true;        if (debug_)        {            System.out.println("ThreadPool : shutting down ");        }        for (int prioIndex = 0; prioIndex <= HIGH_PRIORITY; prioIndex++)        {            List prioThreads = idleThreads_[prioIndex];            for (int threadIndex = 0; threadIndex < prioThreads.size(); threadIndex++)            {                PooledThread idleThread = (PooledThread) prioThreads.get(threadIndex);                idleThread.shutDown();            }        }        notifyAll();        if (debug_)        {            System.out.println("ThreadPool : shutdown done.");        }    }    //以Runnable为target，从池中选择一个优先级为priority的线程创建线程    //并让线程运行。    public synchronized void start(Runnable target, int priority)    {        PooledThread thread = null;  //被选出来执行target的线程        List idleList = idleThreads_[priority];        if (idleList.size() > 0)         {            //如果池中相应优先级的线程有空闲的，那么从中取出一个            //设置它的target，并唤醒它            //从空闲的线程队列中获取            int lastIndex = idleList.size() - 1;            thread = (PooledThread) idleList.get(lastIndex);            idleList.remove(lastIndex);            thread.setTarget(target);        }        //池中没有相应优先级的线程        else         {             threadCreationCounter_++;            // 创建新线程，            thread = new PooledThread(target, "PooledThread #" + threadCreationCounter_, this);            // 新线程放入池中            switch (priority)             {                case LOW_PRIORITY :                {                    thread.setPriority(Thread.MIN_PRIORITY);                    break;                }                case NORMAL_PRIORITY :                {                    thread.setPriority(Thread.NORM_PRIORITY);                    break;                }                case HIGH_PRIORITY :                {                    thread.setPriority(Thread.MAX_PRIORITY);                    break;                }                default :                {                    thread.setPriority(Thread.NORM_PRIORITY);                    break;                }            }            //启动这个线程            thread.start();        }    }}

工作者线程代码：

public class PooledThread extends Thread {    private ThreadPool pool_;  // 池中线程需要知道自己所在的池    private Runnable target_;   // 线程的任务    private boolean shutDown_ = false;    private boolean idle_ = false;//设置是否让线程处于等待状态    private PooledThread() {        super();    }    private PooledThread(Runnable target)    {        super(target); //初始化父类    }    private PooledThread(Runnable target, String name)     {        super(target, name);    }    public PooledThread(Runnable target, String name, ThreadPool pool)    {        super(name);        pool_ = pool;        target_ = target;    }    private PooledThread(String name)     {        super(name);//初始化父类    }    private PooledThread(ThreadGroup group, Runnable target)    {        super(group, target);    }    private PooledThread(ThreadGroup group, Runnable target, String name)     {        super(group, target, name);    }    private PooledThread(ThreadGroup group, String name)     {        super(group, name);    }    public java.lang.Runnable getTarget()     {        return target_;    }    public boolean isIdle()     {        return idle_;//返回当前的状态    }    //工作者线程与通常线程不同之处在于run()方法的不同。通常的线程，    //完成线程应该执行的代码后，自然退出，线程结束。    //虚拟机在线程结束后收回分配给线程的资源，线程对象被垃圾回收。]    //而这在池化的工作者线程中是应该避免的，否则线程池就失去了意义。    //作为可以被放入池中并重新利用的工作者线程，它的run()方法不应该结束，    //随意，在随后可以看到的实现中，run()方法执行完target对象的代码后，    //就将自身repool()，然后调用wait()方法，使自己睡眠而不是退出循环和run()。    //这就使线程池实现的要点。    public void run()     {        // 这个循环不能结束，除非池类要求线程结束        // 每一次循环都会执行一次池类分配给的任务target        while (!shutDown_)         {              idle_ = false;            if (target_ != null)             {                target_.run();  // 运行target中的代码            }            idle_ = true;            try             {                //线程通知池重新将自己放回到池中                pool_.repool(this);  //                 //进入池中后睡眠，等待被唤醒执行新的任务，                //这里是线程池中线程于普通线程的run()不同的地方。                synchronized (this)                 {                    wait();                }            }            catch (InterruptedException ie)            {            }            idle_ = false;        }        //循环这里不能结束，否则线程结束，资源被VM收回，        //就无法起到线程池的作用了    }    public synchronized void setTarget(java.lang.Runnable newTarget)     {//设置新的target，并唤醒睡眠中的线程        target_ = newTarget;  // 新任务        notifyAll();          // 唤醒睡眠的线程    }    public synchronized void shutDown()    {        shutDown_ = true;        notifyAll();    }}

测试代码：

public static void main(String[] args)    {        System.out.println("Testing ThreadPool ");        System.out.println("Creating ThreadPool ");        ThreadPool pool = ThreadPool.instance();        pool.setDebug(true);        class TestRunner implements Runnable         {            public int count = 0;            public void run()             {                System.out.println("Testrunner sleeping 5 seconds ");                //此方法使本线程睡眠5秒                synchronized (this)                 {                    try                     {                        wait(5000);//等待5秒时间                    }                    catch (InterruptedException ioe)                     {                    }                }                System.out.println("Testrunner leaving  ");                count++;            }        }        System.out.println("Starting a new thread ");        TestRunner runner = new TestRunner();        pool.start(runner, pool.HIGH_PRIORITY);        System.out.println("count : " + runner.count);        System.out.println("Thread count : " + pool.getCreatedThreadsCount());        pool.shutdown();    }}

结果

Testing ThreadPool Creating ThreadPool Starting a new thread Testrunner sleeping 5 seconds count : 0Thread count : 1ThreadPool : shutting down ThreadPool : shutdown done.Testrunner leaving ThreadPool.repool() : Destroying incoming thread.ThreadPool.recycle() : done.