MemorySegment.java

/*
 * Copyright (C) 2006-2008 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.jlan.server.filesys.loader;

/**
 * Memory Segment Class
 * 
 * <p>Contains an in-memory copy of file data.
 *
 * @author gkspencer
 */
public class MemorySegment {

	//	Data buffer and file offset
	
	private byte[] m_buffer;
	private long m_fileOff;
	
	//	Read count
	
	private int m_readCount;
	
	/**
	 * Class constructor
	 * 
	 * @param buf byte[]
	 * @param fileOff long
	 */
	public MemorySegment(byte[] buf, long fileOff) {
		m_buffer  = buf;
		m_fileOff = fileOff;
	}
	
	/**
	 * Class constructor
	 * 
	 * @param buf byte[]
	 * @param pos int
	 * @param len int
	 * @param fileOff long
	 */
	public MemorySegment(byte[] buf, int pos, int len, long fileOff) {
		m_buffer = new byte[len];
		System.arraycopy(buf,pos,m_buffer,0,len);
		m_fileOff = fileOff;
	}
	
	/**
	 * Return the buffer
	 * 
	 * @return byte[]
	 */
	public final byte[] getBuffer() {
		return m_buffer;
	}
	
	/**
	 * Return the buffer length
	 * 
	 * @return int
	 */
	public final int getLength() {
		return m_buffer.length;
	}
	
	/**
	 * Return the file offset of the data
	 * 
	 * @return long
	 */
	public final long getFileOffset() {
		return m_fileOff;
	}

	/**
	 * Return the memory segment read count
	 * 
	 * @return int
	 */
	public final int getReadCounter() {
		return m_readCount;
	}
		
	/**
	 * Check if this segment contains the data for the specified request
	 * 
	 * @param fileOff long
	 * @param len int
	 * @return boolean
	 */
	public final boolean containsData(long fileOff, int len) {
		
		//	Check if the memory segment has enough data for the request
		
		if ( len > getLength())
			return false;
			
		//	Check if the memory segment contains the required data
		
		long endOff  = fileOff + len;
		long dataEnd = getFileOffset() + getLength();
		
		if ( fileOff >= getFileOffset() && endOff <= dataEnd)
			return true;
			
		//	Data not in this segment
		
		return false;
	}
	
	/**
	 * Copy data to the specified user buffer
	 * 
	 * @param buf byte[]
	 * @param pos int
	 * @param len int
	 * @param fileOff long
	 */
	public final void copyBytes(byte[] buf, int pos, int len, long fileOff) {
		
		//	Update the file offset
		
		int bufOff = (int) ( fileOff - getFileOffset());
		
		//	Copy data to the user buffer
		
		System.arraycopy(m_buffer,bufOff,buf,pos,len);
		
		//	Update the read count
		
		m_readCount++;
	}
	
	/**
	 * Increment the read counter by the specified amount
	 * 
	 * @param incr int
	 */
	public final void incrementReadCounter(int incr) {
		m_readCount += incr;
	}
	
	/**
	 * Decrement the read counter, if greater than zero
	 * 
	 * @param decr int
	 */
	protected final void decrementReadCounter(int decr) {
		if ( m_readCount > decr)
			m_readCount -= decr;
		else
			m_readCount = 0;
	}

	/**
	 * Decrement the read counter, if greater than zero
	 */
	protected final void decrementReadCounter() {
		decrementReadCounter(1);
	}
	
	/**
	 * Return the memory segment as a string
	 * 
	 * @return String
	 */
	public String toString() {
		StringBuffer str = new StringBuffer();
		str.append("[len=");
		str.append(getLength());
		str.append(",fileOff=");
		str.append(getFileOffset());
		str.append(",reads=");
		str.append(getReadCounter());
		str.append("]");
		
		return str.toString();
	}
}