src/com/plusminus/craft/RegionFileCache.java

/*
 ** 2011 January 5
 **
 ** The author disclaims copyright to this source code.  In place of
 ** a legal notice, here is a blessing:
 **
 **    May you do good and not evil.
 **    May you find forgiveness for yourself and forgive others.
 **    May you share freely, never taking more than you give.
 */

/*
 * 2011 February 16
 * 
 * This source code is based on the work of Scaevolus (see notice above).
 * It has been slightly modified by Mojang AB to limit the maximum cache
 * size (relevant to extremely big worlds on Linux systems with limited
 * number of file handles). The region files are postfixed with ".mcr"
 * (Minecraft region file) instead of ".data" to differentiate from the
 * original McRegion files.
 * 
 */

/*
 * 2011 February 20
 * 
 * Imported by CJ Kucera into X-Ray, from a blog post by Jens Bergensten
 * at: http://mojang.com/2011/02/16/minecraft-save-file-format-in-beta-1-3/
 */

// A simple cache and wrapper for efficiently multiple RegionFiles simultaneously.
package com.plusminus.craft;

import java.io.*;
import java.lang.ref.*;
import java.util.*;

public class RegionFileCache {

    private static final int MAX_CACHE_SIZE = 256;


    private static final Map<File, Reference<RegionFile>> cache = new HashMap<File, Reference<RegionFile>>();

    private RegionFileCache() {
    }

    public static synchronized RegionFile getRegionFile(File basePath, int chunkX, int chunkZ) {
        File regionDir = new File(basePath, "region");
        File file = new File(regionDir, "r." + (chunkX >> 5) + "." + (chunkZ >> 5) + ".mcr");

        Reference<RegionFile> ref = cache.get(file);

        if (ref != null && ref.get() != null) {
            return ref.get();
        }

        /* Commented for X-Ray because I'd rather not modify anything, even if it's just a
         * directory.  We should never get here unless stuff exists, anyway.
        if (!regionDir.exists()) {
            regionDir.mkdirs();
        }
        */

        if (cache.size() >= MAX_CACHE_SIZE) {
            RegionFileCache.clear();
        }

        if (file.exists())
        {
	        RegionFile reg = new RegionFile(file);
	        cache.put(file, new SoftReference<RegionFile>(reg));
	        return reg;
        }
        else
        {
        	return null;
        }
    }

    public static synchronized void clear() {
        for (Reference<RegionFile> ref : cache.values()) {
            try {
                if (ref.get() != null) {
                    ref.get().close();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        cache.clear();
    }

    public static int getSizeDelta(File basePath, int chunkX, int chunkZ) {
        RegionFile r = getRegionFile(basePath, chunkX, chunkZ);
        return r.getSizeDelta();
    }

    public static DataInputStream getChunkDataInputStream(File basePath, int chunkX, int chunkZ) {
        RegionFile r = getRegionFile(basePath, chunkX, chunkZ);
        return r.getChunkDataInputStream(chunkX & 31, chunkZ & 31);
    }
    
    /* Commented for X-Ray since we won't be writing anything
    public static DataOutputStream getChunkDataOutputStream(File basePath, int chunkX, int chunkZ) {
        RegionFile r = getRegionFile(basePath, chunkX, chunkZ);
        return r.getChunkDataOutputStream(chunkX & 31, chunkZ & 31);
    }
    */
}