Java-有效的对象池，具有固定数量的要池对象，并使用等待通知

Question

我正在尝试实现对象池，该对象池具有固定数量的对象供池使用，并在池为空时使用wait，并在线程释放对象时通知。

我可以使用以下程序实现上述必需的功能。

我想知道实施是否正确或需要从Interview角度进行任何修改？

    import java.util.ArrayList;
import java.util.List;

class ObjectPool
{
    static List objects = new ArrayList();
    static
    {
        objects.add("Object One");
        objects.add("Object Two");
    }
    public Object getObject()
    {
            synchronized(objects)
            {
                if(objects.isEmpty())
                {
                    System.out.println(Thread.currentThread().getName()  + " waiting as Object Pool is empty");
                    try {
                        objects.wait();
                        System.out.println(Thread.currentThread().getName()  + " Got Notification");
                    } catch (InterruptedException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }
                }
                Object locked = objects.get(objects.size()-1);
                objects.remove(locked);
                System.out.println(Thread.currentThread().getName()  + " got lock of object : "+ locked);
                return locked;
        }
    }

    public boolean release(Object released)
    {
        synchronized(objects)
        {
        System.out.println(Thread.currentThread().getName() + " releasing Object : "+released);
        objects.notify();
        return objects.add(released);
        }
    }
}


    public class MainforObjectPool implements Runnable
    {
        static ObjectPool p = new ObjectPool();
        public static void main(String[] args)
        {
            MainforObjectPool m = new MainforObjectPool();

            Thread t1 = new Thread(m,"thread 1");
            Thread t2 = new Thread(m,"thread 2");
            Thread t3 = new Thread(m,"thread 3");
            Thread t4 = new Thread(m,"thread 4");
            Thread t5 = new Thread(m,"thread 5");



            t1.start();
            t2.start();
            t3.start();
            t4.start();
            t5.start();


            System.out.println("Main Thread Completed");


        }

        public void run()
        {
            Object locked = p.getObject();
            try {
                Thread.sleep(2000);
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

            p.release(locked);
        }
    }

Answer 1

很久以前，我使用与您的抽象相似的抽象解决了类似的问题。幸运的是，我将其保存并放入here。为了使这个答案简短，希望能用我的话说清楚，我不会在此处发布整个代码。

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实施：

您可以拥有一个具有泛型的抽象类，该类可以使您创建自己喜欢的对象的池。是的，我会像这样使用我的最爱并摆脱它

此抽象类允许其实现者处理创建/过期对象的逻辑。

此类具有锁定和未锁定的对象的队列。

当您checkIn进入池中的对象时，该对象将进入解锁队列中。

当您checkOut从池中访问对象时，它将通过调用抽象方法validate()来检查该对象是否到期。如果此函数返回true，则对象将移至锁定队列。如果此函数返回false，则通过调用抽象函数expire()将对象从池中删除并过期（您可以在其中使用notify）。如果要检查的对象没有被合并，则将其创建并放入锁定队列中。

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代码：

public abstract class ObjectPool<T> {
    private long expirationTime;

    private Hashtable<T, Long> locked, unlocked;

    public ObjectPool() {
        expirationTime = 30000; // 30 seconds
        locked = new Hashtable<T, Long>();
        unlocked = new Hashtable<T, Long>();
    }

    /**
     * Implemented in concrete class. Create an object to be pooled.
     */
    protected abstract T create();

    /**
     * Used to check whether the object should be kept in the lock, or released.
     */
    public abstract boolean validate(T o);

    /**
     * Object expired. (Use notify?)
     */
    public abstract void expire(T o);

    public synchronized T checkOut() {
        long now = System.currentTimeMillis();
        T t;
        if (unlocked.size() > 0) {
            Enumeration<T> e = unlocked.keys();
            while (e.hasMoreElements()) {
                t = e.nextElement();
                if ((now - unlocked.get(t)) > expirationTime) {
                    // object has expired
                    unlocked.remove(t);
                    expire(t);
                    t = null;
                } else {
                    if (validate(t)) {
                        unlocked.remove(t);
                        locked.put(t, now);
                        return (t);
                    } else {
                        // object failed validation
                        unlocked.remove(t);
                        expire(t);
                        t = null;
                    }
                }
            }
        }
        // no objects available, create a new one
        t = create();
        locked.put(t, now);
        return (t);
    }

    public synchronized void checkIn(T t) {
        locked.remove(t);
        unlocked.put(t, System.currentTimeMillis());
    }

    public synchronized long getExpirationTime() {
        return expirationTime;
    }

    public synchronized void setExpirationTime(long expirationTime) {
        this.expirationTime = expirationTime;
    }   

}

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