common/src/main/java/org/apache/abdera2/common/misc/PoolManager.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  The ASF licenses this file to You
 * under the Apache License, Version 2.0 (the "License"); you may not
 * use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.  For additional information regarding
 * copyright in this work, please see the NOTICE file in the top level
 * directory of this distribution.
 */
package org.apache.abdera2.common.misc;

import java.util.Queue;
import java.util.concurrent.ArrayBlockingQueue;


/**
 * Implements a simple pool manager. By default, an upper limit to the pool is set at 25 entries. New items can always
 * be created, but if more than 25 entries are released back to the pool, extras are discarded. Items added to the
 * stack should never maintain any kind of state as it is entirely possible that different threads will be grabbing
 * items from the pool
 */
public abstract class PoolManager<T,R> implements ItemManager<T,R> {

    private static final int DEFAULT_SIZE = 25;
    private final Queue<T> pool;
    private final int cap;
    
    protected PoolManager() {
        this(DEFAULT_SIZE);
    }

    protected PoolManager(int max) {
        this.pool = initStack(max);
        this.cap = max;
    }

    public int currentSize() {
      return pool.size();
    }
    
    private Queue<T> initStack(final int max) {
      return new ArrayBlockingQueue<T>(Math.max(1,max));
    }

    protected T getInstance() {
      T t = pool.poll();
      return t != null ? t : internalNewInstance();
    }

    public synchronized void release(T t) {
        if (t == null) return;
        if (remaining() == 0)
          pool.poll();
        pool.offer(t);
    }

    public int remaining() {
      return cap - pool.size();
    }
    
    protected abstract T internalNewInstance();

    public T get(R request) {
      return getInstance();
    }


}