//******************************************************************************
//
// File:    ResourceCache.java
// Package: edu.rit.pj.cluster
// Unit:    Class edu.rit.pj.cluster.ResourceCache
//
// This Java source file is copyright (C) 2006 by Alan Kaminsky. All rights
// reserved. For further information, contact the author, Alan Kaminsky, at
// ark@cs.rit.edu.
//
// This Java source file is part of the Parallel Java Library ("PJ"). PJ is free
// software; you can redistribute it and/or modify it under the terms of the GNU
// General Public License as published by the Free Software Foundation; either
// version 3 of the License, or (at your option) any later version.
//
// PJ is distributed in the hope that it will be useful, but WITHOUT ANY
// WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
// A PARTICULAR PURPOSE. See the GNU General Public License for more details.
//
// A copy of the GNU General Public License is provided in the file gpl.txt. You
// may also obtain a copy of the GNU General Public License on the World Wide
// Web at http://www.gnu.org/licenses/gpl.html.
//
//******************************************************************************

package edu.rit.pj.cluster;

import java.util.HashMap;
import java.util.Map;

/**
 * Class ResourceCache provides a cache of resources, indexed by resource name.
 * A resource is a piece of content (sequence of bytes) obtained from a class
 * loader.
 * 

 * Note: Class ResourceCache is multiple thread safe.
 *
 * @author  Alan Kaminsky
 * @version 26-Oct-2006
 */
public class ResourceCache
	{

// Hidden data members.

	private Map myMap =
		new HashMap();

// Hidden helper classes.

	private static class ResourceInfo
		{
		public byte[] content;

		public ResourceInfo
			(byte[] content)
			{
			this.content = content;
			}
		}

// Exported constructors.

	/**
	 * Construct a new resource cache.
	 */
	public ResourceCache()
		{
		}

// Exported operations.

	/**
	 * Determine if this resource cache contains resource information for the
	 * given resource name. If the answer is yes, the resource content may or
	 * may not have been found.
	 *
	 * @param  name  Resource name.
	 *
	 * @return  True if this resource cache contains resource information for
	 *          name, false otherwise.
	 */
	public synchronized boolean contains
		(String name)
		{
		ResourceInfo info = myMap.get (name);
		return info != null;
		}

	/**
	 * Determine if this resource cache contains the resource content for the
	 * given resource name. If the answer is yes, the resource content was
	 * found, otherwise the resource content was not found or no resource
	 * information is available.
	 *
	 * @param  name  Resource name.
	 *
	 * @return  True if this resource cache contains the resource content for
	 *          name, false otherwise.
	 */
	public synchronized boolean containsContent
		(String name)
		{
		ResourceInfo info = myMap.get (name);
		return info == null ? false : info.content != null;
		}

	/**
	 * Obtain the resource content for the given resource name from this
	 * resource cache (blocking). This method will block if necessary until this
	 * resource cache contains the content for name or until this
	 * resource cache knows the content was not found.
	 *
	 * @param  name  Resource name.
	 *
	 * @return  Resource content, or null if not found.
	 *
	 * @exception  InterruptedException
	 *     Thrown if the calling thread is interrupted while blocked in this
	 *     method.
	 */
	public synchronized byte[] get
		(String name)
		throws InterruptedException
		{
		ResourceInfo info = myMap.get (name);
		while (info == null)
			{
			wait();
			info = myMap.get (name);
			}
		return info.content;
		}

	/**
	 * Obtain the resource content for the given resource name from this
	 * resource cache (non-blocking). This method will return null if the
	 * resource content was not found or no resource information is available.
	 *
	 * @param  name  Resource name.
	 *
	 * @return  Resource content, or null if not found or no information is
	 *          available.
	 */
	public synchronized byte[] getNoWait
		(String name)
		{
		ResourceInfo info = myMap.get (name);
		return info == null ? null : info.content;
		}

	/**
	 * Store the given resource content under the given resource name in this
	 * resource cache. Any existing content for name is overwritten.
	 * 

	 * Note: The resource cache assumes that the contents of
	 * content are not changed after put() is called.
	 *
	 * @param  name     Resource name.
	 * @param  content  Resource content, or null if not found.
	 */
	public synchronized void put
		(String name,
		 byte[] content)
		{
		myMap.put (name, new ResourceInfo (content));
		notifyAll();
		}

	/**
	 * Remove the resource content for the given resource name from this
	 * resource cache. If there is no content for name, the
	 * remove() method does nothing.
	 *
	 * @param  name  Resource name.
	 */
	public synchronized void remove
		(String name)
		{
		myMap.remove (name);
		}

	}