core/org.eclipse.stem.core/src/org/eclipse/stem/core/STEMObjectPool.java

package org.eclipse.stem.core;

import java.util.ArrayList;


/*******************************************************************************
 * Copyright (c) 2012 IBM Corporation and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/


/**
 * A simple object pool used to avoid excessive object creation. The pool allows clients to retrieve pre-initialized objects of a given 
 * kind from a pool of available objects. When retrieved, the object becomes unavailable and other clients cannot use it concurrently.
 * The client must make sure to return the object to the pool when done with it.
 * 
 * You specify the type of the object by passing a sample and the clone() method is used to create new instances.
 * 
 * Clients must implement the createNewObject() method
 * 
 * TODO: Periodically maintain the size of the pool and shrink when not used
 * @author edlund
 *
 */
public abstract class STEMObjectPool {

	ArrayList<Object> freeObjects = new ArrayList<Object>(); 
	int growthInc;
	
	@SuppressWarnings("rawtypes")
	public STEMObjectPool(int initialSize, int growthIncrement) {
		this.growthInc = growthIncrement <=0? 1:growthIncrement; // safe
		
		try {
			for(int i=0;i<initialSize;++i)
				freeObjects.add(createNewObject());
		} catch(Exception e) {
			CorePlugin.logError("Error growing STEM object pool", e);
		}
	}
	
	public synchronized Object get()  {
		if(freeObjects.size() > 0)
			return freeObjects.remove(freeObjects.size()-1);
		// Grow pool
		try {
			for(int i=0;i<growthInc;++i) {
				freeObjects.add(createNewObject());
			}
		} catch(Exception e) {
			CorePlugin.logError("Error growing STEM object pool", e);
		}
		return freeObjects.remove(freeObjects.size()-1);
	}
	
	public synchronized void release(Object o) {
		freeObjects.add(o);
	}
	
	protected abstract Object createNewObject(); // Must be implemented by subclass
	
}