src/java/org/apache/fulcrum/pool/DefaultPoolService.java

package org.apache.fulcrum.pool;

import java.util.HashMap;

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  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.
 */

import java.util.Map;

import org.apache.avalon.framework.activity.Disposable;
import org.apache.avalon.framework.activity.Initializable;
import org.apache.avalon.framework.configuration.Configurable;
import org.apache.avalon.framework.configuration.Configuration;
import org.apache.avalon.framework.logger.AbstractLogEnabled;
import org.apache.avalon.framework.service.ServiceManager;
import org.apache.avalon.framework.service.Serviceable;
import org.apache.fulcrum.factory.FactoryException;
import org.apache.fulcrum.factory.FactoryService;

/**
 * The Pool Service extends the Factory Service by adding support for pooling
 * instantiated objects. When a new instance is requested, the service first
 * checks its pool if one is available. If the the pool is empty, a new instance
 * will be requested from the FactoryService.
 *
 * For objects implementing the Recyclable interface, a recycle method will be
 * called, when they taken from the pool, and a dispose method, when they are
 * returned to the pool.
 *
 * @author <a href="mailto:ilkka.priha@simsoft.fi">Ilkka Priha</a>
 * @author <a href="mailto:mcconnell@apache.org">Stephen McConnell</a>
 * @version $Id$
 *
 * avalon.component name="pool" lifestyle="transient"
 * avalon.service type="org.apache.fulcrum.pool.PoolService"
 */
public class DefaultPoolService extends AbstractLogEnabled
		implements PoolService, Serviceable, Disposable, Initializable, Configurable {
	/**
	 * The property specifying the pool capacity.
	 */
	public static final String POOL_CAPACITY = "capacity";
	
	/**
	 * The default capacity of pools.
	 */
	private int poolCapacity = DEFAULT_POOL_CAPACITY;
	
	/**
	 * The pool repository, one pool for each class.
	 */
	private HashMap<String, PoolBuffer> poolRepository = new HashMap<>();
	private Map<String, Integer> capacityMap;
	private FactoryService factoryService;
	private ServiceManager manager;

	/**
	 * Gets an instance of a named class either from the pool or by calling the
	 * Factory Service if the pool is empty.
	 *
	 * @param className the name of the class.
	 * @return the instance.
	 * @throws PoolException if recycling fails.
	 */
	public <T> T getInstance(String className) throws PoolException 
	{
		try 
		{
			T instance = pollInstance(className, null, null);
			return instance == null ? getFactory().getInstance(className) : instance;
		} 
		catch (FactoryException fe) 
		{
			throw new PoolException(fe);
		}
	}

	/**
	 * Gets an instance of a named class either from the pool or by calling the
	 * Factory Service if the pool is empty. The specified class loader will be
	 * passed to the Factory Service.
	 *
	 * @param className the name of the class.
	 * @param loader    the class loader.
	 * @return the instance.
	 * @throws PoolException if recycling fails.
	 */
	public Object getInstance(String className, ClassLoader loader) throws PoolException 
	{
		try 
		{
			Object instance = pollInstance(className, null, null);
			return instance == null ? getFactory().getInstance(className, loader) : instance;
		} 
		catch (FactoryException fe) 
		{
			throw new PoolException(fe);
		}
	}

	/**
	 * Gets an instance of a named class either from the pool or by calling the
	 * Factory Service if the pool is empty. Parameters for its constructor are
	 * given as an array of objects, primitive types must be wrapped with a
	 * corresponding class.
	 *
	 * @param className the name of the class.
	 * @param params    an array containing the parameters of the constructor.
	 * @param signature an array containing the signature of the constructor.
	 * @return the instance.
	 * @throws PoolException if recycling fails.
	 */
	public Object getInstance(String className, Object[] params, String[] signature) throws PoolException 
	{
		try 
		{
			Object instance = pollInstance(className, params, signature);
			return instance == null ? getFactory().getInstance(className, params, signature) : instance;
		} 
		catch (FactoryException fe) 
		{
			throw new PoolException(fe);
		}
	}

	/**
	 * Gets an instance of a named class either from the pool or by calling the
	 * Factory Service if the pool is empty. Parameters for its constructor are
	 * given as an array of objects, primitive types must be wrapped with a
	 * corresponding class. The specified class loader will be passed to the Factory
	 * Service.
	 *
	 * @param className the name of the class.
	 * @param loader    the class loader.
	 * @param params    an array containing the parameters of the constructor.
	 * @param signature an array containing the signature of the constructor.
	 * @return the instance.
	 * @throws PoolException if recycling fails.
	 */
	public Object getInstance(String className, ClassLoader loader, Object[] params, String[] signature)
			throws PoolException 
	{
		try 
		{
			Object instance = pollInstance(className, params, signature);
			return instance == null ? getFactory().getInstance(className, loader, params, signature) : instance;
		} 
		catch (FactoryException fe) 
		{
			throw new PoolException(fe);
		}
	}

	/**
	 * Tests if specified class loaders are supported for a named class.
	 *
	 * @param className the name of the class.
	 * @return true if class loaders are supported, false otherwise.
	 * @throws FactoryException if test fails.
	 */
	public boolean isLoaderSupported(String className) throws FactoryException 
	{
		return getFactory().isLoaderSupported(className);
	}

	/**
	 * Gets an instance of a specified class either from the pool or by instatiating
	 * from the class if the pool is empty.
	 *
	 * @param <T> type of the class
	 * @param clazz the class.
	 * @return the instance.
	 * @throws PoolException if recycling fails.
	 */
	@SuppressWarnings("unchecked")
	public <T> T getInstance(Class<?> clazz) throws PoolException 
	{
		try 
		{
			T instance = pollInstance(clazz.getName(), null, null);
			return instance == null ? (T) factoryService.getInstance(clazz) : instance;
		} 
		catch (FactoryException fe) 
		{
			throw new PoolException(fe);
		}
	}

	/**
	 * Gets an instance of a specified class either from the pool or by instatiating
	 * from the class if the pool is empty.
	 *
	 * @param clazz     the class.
	 * @param params    an array containing the parameters of the constructor.
	 * @param signature an array containing the signature of the constructor.
	 * @return the instance.
	 * @throws PoolException if recycling fails.
	 */
	public <T> T getInstance(Class<?> clazz, Object params[], String signature[]) throws PoolException 
	{
		try 
		{
			T instance = pollInstance(clazz.getName(), params, signature);
			
			// TODO There is a whacky .toString() on the clazz object, 
			// but otherwise it won't compile
			return instance == null ? getFactory().getInstance(clazz.toString(), params, signature) : instance;
			
		} 
		catch (FactoryException fe) 
		{
			throw new PoolException(fe);
		}
	}

	/**
	 * Puts a used object back to the pool. Objects implementing the Recyclable
	 * interface can provide a recycle method to be called when they are reused and
	 * a dispose method to be called when they are returned to the pool.
	 *
	 * @param instance the object instance to recycle.
	 * @return true if the instance was accepted.
	 */
	@SuppressWarnings("unchecked")
	public boolean putInstance(Object instance) 
	{
		if (instance != null) 
		{
			HashMap<String, PoolBuffer> repository = poolRepository;
			String className = instance.getClass().getName();
			PoolBuffer pool = (PoolBuffer) repository.get(className);
			if (pool == null) 
			{
				pool = new PoolBuffer(getCapacity(className));
				repository = (HashMap<String, PoolBuffer>) repository.clone();
				repository.put(className, pool);
				poolRepository = repository;
				if (instance instanceof ArrayCtorRecyclable) 
				{
					pool.setArrayCtorRecyclable(true);
				}
			}
			return pool.offer(instance);
		} else {
			return false;
		}
	}

	/**
	 * Gets the capacity of the pool for a named class.
	 *
	 * @param className the name of the class.
	 */
	public int getCapacity(String className) 
	{
		PoolBuffer pool = (PoolBuffer) poolRepository.get(className);
		if (pool == null) 
		{
			/* Check class specific capacity. */
			int capacity = poolCapacity;
			if (capacityMap != null) 
			{
				Integer cap = (Integer) capacityMap.get(className);
				if (cap != null) 
				{
					capacity = cap.intValue();
				}
			}
			return capacity;
		} else {
			return pool.capacity();
		}
	}

	/**
	 * Sets the capacity of the pool for a named class. Note that the pool will be
	 * cleared after the change.
	 *
	 * @param className the name of the class.
	 * @param capacity  the new capacity.
	 */
	@SuppressWarnings("unchecked")
	public void setCapacity(String className, int capacity) 
	{
		HashMap<String, PoolBuffer> repository = poolRepository;
		repository = repository != null ? (HashMap<String, PoolBuffer>) repository.clone()
				: new HashMap<String, PoolBuffer>();
		repository.put(className, new PoolBuffer(capacity));
		poolRepository = repository;
	}

	/**
	 * Gets the current size of the pool for a named class.
	 *
	 * @param className the name of the class.
	 */
	public int getSize(String className) 
	{
		PoolBuffer pool = (PoolBuffer) poolRepository.get(className);
		return pool != null ? pool.size() : 0;
	}

	/**
	 * Clears instances of a named class from the pool.
	 *
	 * @param className the name of the class.
	 */
	@SuppressWarnings("unchecked")
	public void clearPool(String className) 
	{
		HashMap<String, PoolBuffer> repository = poolRepository;
		if (repository.get(className) != null) 
		{
			repository = (HashMap<String, PoolBuffer>) repository.clone();
			repository.remove(className);
			poolRepository = repository;
		}
	}

	/**
	 * Clears all instances from the pool.
	 */
	public void clearPool() 
	{
		poolRepository = new HashMap<String, PoolBuffer>();
	}

	/**
	 * Polls and recycles an object of the named class from the pool.
	 *
	 * @param className the name of the class.
	 * @param params    an array containing the parameters of the constructor.
	 * @param signature an array containing the signature of the constructor.
	 * @return the object or null.
	 * @throws PoolException if recycling fails.
	 */
	private <T> T pollInstance(String className, Object[] params, String[] signature) throws PoolException 
	{
		PoolBuffer pool = (PoolBuffer) poolRepository.get(className);
		return pool != null ? pool.poll(params, signature, factoryService) : null;
	}

	/**
	 * Gets the factory service.
	 *
	 * @return the factory service.
	 */
	protected FactoryService getFactory() 
	{
		return factoryService;
	}

	// ---------------- Avalon Lifecycle Methods ---------------------
	/* (non-Javadoc)
	 * Avalon component lifecycle method
	 * @see org.apache.avalon.framework.configuration.Configurable#configure(org.apache.avalon.framework.configuration.Configuration)
	 */
	public void configure(Configuration conf) 
	{
		final Configuration capacities = conf.getChild(POOL_CAPACITY, false);
		if (capacities != null) 
		{
			Configuration defaultConf = capacities.getChild("default");
			int capacity = defaultConf.getValueAsInteger(DEFAULT_POOL_CAPACITY);
			if (capacity <= 0) 
			{
				throw new IllegalArgumentException("Capacity must be >0");
			}
			poolCapacity = capacity;
			Configuration[] nameVal = capacities.getChildren();
			for (int i = 0; i < nameVal.length; i++) 
			{
				String key = nameVal[i].getName();
				if (!"default".equals(key)) 
				{
					capacity = nameVal[i].getValueAsInteger(poolCapacity);
					if (capacity < 0) 
					{
						capacity = poolCapacity;
					}
					
					if (capacityMap == null) 
					{
						capacityMap = new HashMap<String, Integer>();
					}
					
					capacityMap.put(key, capacity);
				}
			}
		}
	}

	/**
	 * Avalon component lifecycle method
	 * 
	 * {@link org.apache.fulcrum.factory.FactoryService}
	 * 
	 * @param manager the service manager
	 */
	public void service(ServiceManager manager) 
	{
		this.manager = manager;
	}

	/**
	 * Avalon component lifecycle method Initializes the service by loading default
	 * class loaders and customized object factories.
	 *
	 * @throws Exception if initialization fails.
	 */
	public void initialize() throws Exception 
	{
		try 
		{
			factoryService = (FactoryService) manager.lookup(FactoryService.ROLE);
		} 
		catch (Exception e) 
		{
			throw new Exception("DefaultPoolService.initialize: Failed to get a Factory object", e);
		}
	}

	/**
	 * Avalon component lifecycle method
	 */
	public void dispose() 
	{
		if (factoryService != null) 
		{
			manager.release(factoryService);
		}
		factoryService = null;
		manager = null;
	}
}