ObjectPool.java

/**
 * Copyright (C) 2009 Michael A. MacDonald
 */
package com.iiordanov.util;

/**
 * A pool of reusable object of a given type.  You get the object from a Entry, which you get
 * by calling reserve().  When you are done with the object, you call release() passing the Entry.
 * <p>
 * Failing to call release() does not leak memory--but you will not get the benefits
 * of reusing the object. You will run into contention issues if you
 * call release() while still holding a reference to the pool object.
 * @author Michael A. MacDonald
 *
 */
public abstract class ObjectPool<R> {
    public static class Entry<S> {
        S item;
        Entry<S> nextEntry;
        
        Entry(S i, Entry<S> n)
        {
            item = i;
            nextEntry = n;
        }
        
        public S get() {
            return item;
        }
    }
    
    private Entry<R> next;
    public ObjectPool()
    {
        next = null;
    }
    
    public Entry<R> reserve()
    {
        if (next == null)
        {
            next = new Entry<R>(itemForPool(), null);
        }
        Entry<R> result = next;
        next = result.nextEntry;
        result.nextEntry = null;
        
        return result;
    }
    
    public void release(Entry<R> entry)
    {
        entry.nextEntry = next;
        next = entry;
    }
    
    protected abstract R itemForPool();
}