nodespacemanager.java

支持并发访问的B+树

/*
 * Created on Nov 19, 2004
 *
 * TODO To change the template for this generated file go to
 * Window - Preferences - Java - Code Style - Code Templates
 */
package com.nay0648.ds.bplustree;
import java.io.*;
import java.nio.*;
import java.nio.channels.*;
import java.util.*;

/**
 * Description:<br>
 * this is used to manage file space.all space's allocate or recycle
 * must use this class
 * @abstract
 * @keywords
 * @author nay0648
 * @version last modified:Jun 6, 2004
 */
class NodeSpaceManager
{
private String path;//tree file path
private ByteBuffer buff;//buffer used to increase the file length
private List space;//the empty node list
	
	/**
	 * @param path 
	 * the tree file path
	 * @param nodelength 
	 * a node length mesured in byte
	 */
	public NodeSpaceManager(String path,int nodelength)
	{
		this.path=path;
		//init buffer equal to the node length filled with 0x00
		buff=ByteBuffer.allocate(nodelength);
		for(;buff.position()<buff.capacity();) buff.put((byte)0x00);
		buff.flip();
		//the empty node list
		space=new LinkedList();
	}
	
	/**
	 * allocate a new space for a node at the end of
	 * the file
	 * @param ch
	 * file channel
	 * @return
	 * @throws IOException
	 */
	public synchronized long allocate(FileChannel ch) throws IOException
	{
		long pointer=BPlusTree.NULL;
		
		//if there are empty node in space list,allocate a first one
		if(space.size()>0) return ((Long)space.remove(0)).longValue();
		//no empty space in list,allocate from the end of the tree file
		else
		{
			pointer=ch.size();//the new space's pointer at the end of the file
			//cover this space
			ch.position(pointer);
			if(ch.write(buff)!=buff.capacity()) throw new IOBufferSizeError();
			buff.rewind();
		}
		return pointer;
	}
	
	/**
	 * allocate a space for a node at the specified position
	 * if there is not have empty node space left
	 * @param ch
	 * file channel
	 * @param position
	 * specified position
	 * @return
	 * @throws IOException
	 */
	public synchronized long allocate(FileChannel ch,long position) throws IOException
	{
		long pointer;
		
		//if there are empty node in space list,allocate a first one
		if(space.size()>0) return ((Long)space.remove(0)).longValue();
		//no empty space in list,allocate from the end of the tree file
		else
		{
			pointer=position;//the new space's pointer at the end of the file
			//cover this space
			ch.position(pointer);
			if(ch.write(buff)!=buff.capacity()) throw new IOBufferSizeError();
			buff.rewind();
		}
		return pointer;
	}

	/**
	 * recycle a node's space
	 * @param pointer the address of the first byte of the node space
	 */
	public synchronized void recycle(long pointer)
	{
		space.add(new Long(pointer));
	}

	/**
	 * get the space list size
	 * @return
	 */
	public int size()
	{
		return space.size();
	}
	
	/**
	 * get a specified pointer
	 * @param index
	 * pointer index
	 * @return
	 */
	public long getPointer(int index)
	{
		return ((Long)space.get(index)).longValue();
	}
	
	public String toString()
	{
		return space.toString();
	}

	/*
	public static void main(String[] args) throws Exception
	{}
	*/
}