PooledPagingByteArray.java

package ager;

import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;

public class PooledPagingByteArray {
    public static class Pool {
        private RandomAccessFile raf;
        private long offset = 0;

        public Pool() throws IOException {
            raf = new RandomAccessFile(File.createTempFile("bpp", null), "rw");
        }
        
        public PooledPagingByteArray getArray(int size) { return new PooledPagingByteArray(size, this); }
    }
    
    public final Pool pool;
    public byte[] array;
    public final int size;
    private long offset = -1;
    
    private PooledPagingByteArray(int size, Pool pool) { this.size = size; this.pool = pool; }
    
    public byte[] get() throws IOException {
        if (array == null) {
            pageIn();
        }
        return array;
    }
    
    public void pageIn() throws IOException {
        if (offset == -1) {
            array = new byte[size];
        } else {
            pool.raf.seek(offset);
            pool.raf.read(array);
        }
    }
    
    public void pageOut() throws IOException {
        if (offset == -1) {
            offset = pool.offset;
            pool.offset += size;
        }
        pool.raf.seek(offset);
        pool.raf.write(array);
    }
    
    public static void main(String[] args) throws IOException {
        Pool p = new Pool();
        long ms = System.currentTimeMillis();
        PooledPagingByteArray[] pbas = new PooledPagingByteArray[100];
        for (int i = 0; i < 100; i++) { pbas[i] = p.getArray(4096); }
        for (int i = 0; i < 100; i++) {
            for (int j = 0; j < 100; j++) {
                pbas[j].get();
            }
            for (int j = 0; j < 100; j++) {
                pbas[j].pageOut();
            }
        }
        System.out.println(System.currentTimeMillis() - ms);
    }
}