Java一个简单的线程池实现

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();
????????}
????}
}

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,?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();
????}
}

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();
????}
}