LargeByteBuffer.java

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package edu.rice.cs.hpc.data.util;

import java.io.IOException;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;

public class LargeByteBuffer
{
    
    private MappedByteBuffer[] masterBuffer;
    
    private long length;
    
    final private FileChannel fcInput;
    
    // The page size has to be the multiple of record size (24) and header size (can be 24 or 32)
    // originally: Integer.MAX_VALUE;
    private long pageSize; 
    
    /***
     * Construct direct/indirect mapped byte buffer
     * 
     * @param in : file channel
     * @param headerSz : the size of the header file
     * 
     * @throws IOException
     */
    public LargeByteBuffer(FileChannel in, int headerSz, int recordSz)
        throws IOException
    {
        fcInput = in;
        length = in.size();
        
        // --------------------------------------------------------------------
        // compute the page size:
        // the page size has to be multiple of the least common multiple of 
        //  the header size and the record size
        // --------------------------------------------------------------------
        pageSize = lcm (headerSz, recordSz) * (1 << 20);
        
        int numPages = 1+(int) (in.size() / pageSize);
        masterBuffer = new MappedByteBuffer[numPages];      
    }
    
    private long getCurrentSize(long index) throws IOException 
    {
        long currentSize = pageSize;
        if (length/pageSize == index) {
            currentSize = length - (index * pageSize);
        }
        return currentSize;
    }
    
    /****
     * Set a buffer map to a specified page
     *  
     * @param page
     * @return
     * @throws IOException
     */
    private MappedByteBuffer setBuffer(int page) throws IOException
    {
        long start = page * pageSize;
        MappedByteBuffer buffer = fcInput.map(FileChannel.MapMode.READ_ONLY, start, 
                getCurrentSize(page));
        masterBuffer[page] = buffer;
        
        return buffer;
    }
    
    private MappedByteBuffer getBuffer(int page) throws IOException
    {
        MappedByteBuffer buffer = masterBuffer[page];
        if (buffer == null) {
            buffer = setBuffer(page);
        }
        return buffer;
    }
    
    public byte get(long position) throws IOException
    {
        int page = (int) (position / pageSize);
        int loc = (int) (position % pageSize);
        
        return getBuffer(page).get(loc);
    }
    
    public int getInt(long position) throws IOException
    {
        int page = (int) (position / pageSize);
        int loc = (int) (position % pageSize);
        return getBuffer(page).getInt(loc);
    }
    
    public long getLong(long position) throws IOException
    {
        int page = (int) (position / pageSize);
        int loc = (int) (position % pageSize);
        if (loc < pageSize - 4) {
            return getBuffer(page).getLong(loc);
        } else {
            return (((long) getBuffer(page).getInt(loc)) << 32) + getBuffer(page+1).getInt(0);
        }
    }
    
    public double getDouble(long position) throws IOException
    {
        int page = (int) (position / pageSize);
        int loc = (int) (position % pageSize);
        if (loc < pageSize - 4) {
            return getBuffer(page).getDouble(loc);
        } else {
            return (double)(((long) getBuffer(page).getInt(loc)) << 32) + (long) getBuffer(page+1).getInt(0);
        }
    }
    
    public char getChar(long position) throws IOException
    {
        int page = (int) (position / pageSize);
        int loc = (int) (position % pageSize);
        return getBuffer(page).getChar(loc);
    }

    public String getString(long position, long length) throws IOException
    {
        String str = "";
        for (long i = 0; i < length; ++i) {
            char c = (char)get(position + i);
            str += c;
        }
        return str;
    }

    public float getFloat(long position) throws IOException
    {
        int page = (int) (position / pageSize);
        int loc = (int) (position % pageSize);
        return getBuffer(page).getFloat(loc);
    }
    
    public short getShort(long position) throws IOException
    {
        int page = (int) (position / pageSize);
        int loc = (int) (position % pageSize);
        return getBuffer(page).getShort(loc);
    }
    
    public long size()
    {
        return length;
    }
    
    /***
     * Disposing resources manually to avoid memory leak
     */
    public void dispose() 
    {
        masterBuffer = null;
        try {
            fcInput.close();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
    
    /***
     * compute the gcd of two numbers
     * 
     * @param a
     * @param b
     * @return
     */
    private static long gcd(long a, long b)
    {
        while (b > 0)
        {
            long temp = b;
            b = a % b; 
            a = temp;
        }
        return a;
    }
    
    /****
     * compute the lcm of two numbers
     * 
     * @param a
     * @param b
     * @return
     */
    private static long lcm(long a, long b)
    {
        return a * (b / gcd(a, b));
    }
}