java - Java - 具有固定数量的对象的有效对象池要池化并使用等待通知

Question

我正在尝试实现对象池，它具有固定数量的可用于池的对象，如果池为空，则使用等待，并在线程释放对象时通知。

我可以使用下面的程序来实现上述所需的功能。

我想知道实施是否正确或需要从面试的角度进行任何修改？

    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);
        }
    }

标签： javadesign-patternsobject-poolingobjectpool

Answer 1

很久以前，我使用类似于您的抽象解决了类似的问题。幸运的是，我保存了它并放在这里。为了保持这个答案简短并希望我的话清楚，我不会在这里发布整个代码。

---

执行：

您可以拥有一个具有泛型的抽象类，它可以让您创建自己喜欢的对象的池。是的，我会像这样使用最喜欢的并逃脱它

这个抽象类让其实现者处理创建/过期对象的逻辑。

此类有一个用于锁定和解锁对象的队列。

当您checkIn在池中找到一个对象时，它会进入未锁定队列。

当您checkOut从池中获取对象时，它会通过调用抽象方法来检查对象是否应该过期validate()。如果此函数返回true，则将对象移至锁定队列。如果此函数返回false，则该对象将从池中删除并通过调用抽象函数过期expire()（您可以notify在 this 中使用）。如果要检出的对象没有被池化，那么它会被创建并放入锁定队列中。

---

编码：

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;
    }   

}

---

• 参考链接