/*
 * Copyright (C) 2005-2007 Alfresco Software Limited.
 *
 * This program 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 2
 * of the License, or (at your option) any later version.

 * This program 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.

 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 * As a special exception to the terms and conditions of version 2.0 of
 * the GPL, you may redistribute this Program in connection with Free/Libre
 * and Open Source Software ("FLOSS") applications as described in Alfresco's
 * FLOSS exception.  You should have recieved a copy of the text describing
 * the FLOSS exception, and it is also available here:
 * http://www.alfresco.com/legal/licensing" */
package org.alfresco.filesys.server.oncrpc;

import java.util.*;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

/**
 * Rpc Packet Pool Class
 * 
 * <p>Contains a pool of small and large RpcPacket objects for use by multi-threaded RPC servers.
 * 
 * @author GKSpencer
 */
public class RpcPacketPool {

	// Debug logging

	private static final Log logger = LogFactory.getLog(RpcPacketPool.class);
	
	//	Constants
	//
	//	Default small/large packet sizes

	public static final int DefaultSmallSize 	= 512;
	public static final int DefaultLargeSize 	= 32768;
	public static final int DefaultSmallLimit 	= -1; //	no allocation limit
	public static final int DefaultLargeLimit 	= -1; //   "      "       "

	//	Small/large packet lists

	private Vector m_smallPackets;
	private Vector m_largePackets;

	//	Small packet size and maximum allowed packets

	private int m_smallPktSize;
	private int m_smallPktLimit;

	//	Large packet size and maximum allowed packets

	private int m_largePktSize;
	private int m_largePktLimit;

	//	Count of allocated small/large packets

	private int m_smallPktCount;
	private int m_largePktCount;

	/**
	 * Default constructor
	 */
	public RpcPacketPool()
	{

		// Create the small/large packet lists

		m_smallPackets = new Vector();
		m_largePackets = new Vector();

		// Set the packet sizes/limits

		m_smallPktSize = DefaultSmallSize;
		m_smallPktLimit = DefaultSmallLimit;

		m_largePktSize = DefaultLargeSize;
		m_largePktLimit = DefaultLargeLimit;

	}

	/**
	 * Class constructor
	 * 
	 * @param smallSize int
	 * @param smallLimit int
	 * @param largeSize int
	 * @param largeLimit int
	 */
	public RpcPacketPool(int smallSize, int smallLimit, int largeSize, int largeLimit)
	{

		// Create the small/large packet lists

		m_smallPackets = new Vector();
		m_largePackets = new Vector();

		// Save the packet sizes/limits

		m_smallPktSize = smallSize;
		m_smallPktLimit = smallLimit;

		m_largePktSize = largeSize;
		m_largePktLimit = largeLimit;
	}

	/**
	 * Class constructor
	 * 
	 * @param largeSize int
	 * @param largeLimit int
	 */
	public RpcPacketPool(int largeSize, int largeLimit)
	{

		// Create the small/large packet lists

		m_smallPackets = new Vector();
		m_largePackets = new Vector();

		// Save the packet sizes/limits

		m_smallPktSize = DefaultSmallSize;
		m_smallPktLimit = largeLimit;

		m_largePktSize = largeSize;
		m_largePktLimit = largeLimit;
	}

	/**
	 * Return the small packet size
	 * 
	 * @return int
	 */
	public final int getSmallPacketSize()
	{
		return m_smallPktSize;
	}

	/**
	 * Return the count of allocated small packets
	 * 
	 * @return int
	 */
	public final int getSmallPacketCount()
	{
		return m_smallPktCount;
	}

	/**
	 * Return the small packet allocation limit
	 * 
	 * @return int
	 */
	public final int getSmallPacketAllocationLimit()
	{
		return m_smallPktLimit;
	}

	/**
	 * Return the count of available large packets
	 * 
	 * @return int
	 */
	public final int availableLargePackets()
	{
		return m_largePackets.size();
	}

	/**
	 * Return the large packet size
	 * 
	 * @return int
	 */
	public final int getLargePacketSize()
	{
		return m_largePktSize;
	}

	/**
	 * Return the count of allocated large packets
	 * 
	 * @return int
	 */
	public final int getLargePacketCount()
	{
		return m_largePktCount;
	}

	/**
	 * Return the large packet allocation limit
	 * 
	 * @return int
	 */
	public final int getLargePacketAllocationLimit()
	{
		return m_largePktLimit;
	}

	/**
	 * Return the count of available small packets
	 * 
	 * @return int
	 */
	public final int availableSmallPackets()
	{
		return m_smallPackets.size();
	}

	/**
	 * Allocate a packet from the packet pool
	 * 
	 * @param reqSize int
	 * @return RpcPacket
	 */
	public final RpcPacket allocatePacket(int reqSize)
	{

		// Check if the packet should come from the small or large packet list

		RpcPacket pkt = null;

		if (reqSize <= m_smallPktSize)
		{

			// Allocate a packet from the small packet list

			pkt = allocateSmallPacket();

			// DEBUG

			if (logger.isDebugEnabled())
				logger.debug("RpcPacketPool Allocated (small) " + pkt.getBuffer() + ", len=" + pkt.getBuffer().length
						+ ", list=" + m_smallPackets.size() + "/" + m_smallPktLimit);
		} else
		{

			// Allocate a packet from the large packet list

			pkt = allocateLargePacket();

			// DEBUG

			if (logger.isDebugEnabled())
				logger.debug("RpcPacketPool Allocated (large) " + pkt.getBuffer() + ", len=" + pkt.getBuffer().length
						+ ", list=" + m_largePackets.size() + "/" + m_largePktLimit);
		}

		// Return the allocated packet

		return pkt;
	}

	/**
	 * Release an RPC packet back to the pool
	 * 
	 * @param pkt RpcPacket
	 */
	public final void releasePacket(RpcPacket pkt)
	{

		// Check if the packet should be released to the small or large list

		if (pkt.getBuffer().length >= m_largePktSize)
		{

			// Release the packet to the large packet list

			synchronized (m_largePackets)
			{

				// Add the packet back to the free list

				m_largePackets.addElement(pkt);

				// Signal any waiting threads that there are packets available

				m_largePackets.notify();

				// DEBUG

				if (logger.isDebugEnabled())
					logger.debug("RpcPacketPool Released (large) " + pkt.getBuffer() + ", len="
							+ pkt.getBuffer().length + ", list=" + m_largePackets.size());
			}
		} else
		{

			// Release the packet to the small packet list

			synchronized (m_smallPackets)
			{

				// Add the packet back to the free list

				m_smallPackets.addElement(pkt);

				// Signal any waiting threads that there are packets available

				m_smallPackets.notify();

				// DEBUG

				if (logger.isDebugEnabled())
					logger.debug("RpcPacketPool Released (small) " + pkt.getBuffer() + ", len="
							+ pkt.getBuffer().length);
			}
		}
	}

	/**
	 * Allocate, or create, a small RPC packet
	 * 
	 * @return RpcPacket
	 */
	private final RpcPacket allocateSmallPacket()
	{

		RpcPacket pkt = null;

		synchronized (m_smallPackets)
		{

			// Check if there is a packet available from the small packet list

			if (m_smallPackets.size() > 0)
			{

				// Remove a packet from the head of the free list

				pkt = (RpcPacket) m_smallPackets.elementAt(0);
				m_smallPackets.removeElementAt(0);
			} else if (m_smallPktLimit == -1 || m_smallPktCount < m_smallPktLimit)
			{

				// Allocate a new packet

				pkt = new RpcPacket(m_smallPktSize, this);
				m_smallPktCount++;
			} else
			{

				// Wait for a packet to be released to the small packet list

				try
				{

					// Wait for a packet

					m_smallPackets.wait();

					// Try to get the packet from the small packet list again

					if (m_smallPackets.size() > 0)
					{

						// Remove a packet from the head of the free list

						pkt = (RpcPacket) m_smallPackets.elementAt(0);
						m_smallPackets.removeElementAt(0);
					}
				} catch (InterruptedException ex)
				{
				}
			}
		}

		// Return the allocated packet

		return pkt;
	}

	/**
	 * Allocate, or create, a large RPC packet
	 * 
	 * @return RpcPacket
	 */
	private final RpcPacket allocateLargePacket()
	{

		RpcPacket pkt = null;

		synchronized (m_largePackets)
		{

			// Check if there is a packet available from the large packet list

			if (m_largePackets.size() > 0)
			{

				// Remove a packet from the head of the free list

				pkt = (RpcPacket) m_largePackets.elementAt(0);
				m_largePackets.removeElementAt(0);
			} else if (m_largePktLimit == -1 || m_largePktCount < m_largePktLimit)
			{

				// Allocate a new packet

				pkt = new RpcPacket(m_largePktSize, this);
				m_largePktCount++;
			} else
			{

				// Wait for a packet to be released to the large packet list

				try
				{

					// Wait for a packet

					m_largePackets.wait();

					// Try to get the packet from the large packet list again

					if (m_largePackets.size() > 0)
					{

						// Remove a packet from the head of the free list

						pkt = (RpcPacket) m_largePackets.elementAt(0);
						m_largePackets.removeElementAt(0);
					}
				} catch (InterruptedException ex)
				{
				}
			}
		}

		// Return the allocated packet

		return pkt;
	}
}
