yacy_search_server/source/de/anomic/index/indexContainerBLOBArray.java

// indexContainerBLOBHeap.java
// (C) 2009 by Michael Peter Christen; mc@yacy.net, Frankfurt a. M., Germany
// first published 04.01.2009 on http://yacy.net
//
// This is a part of YaCy, a peer-to-peer based web search engine
//
// $LastChangedDate: 2008-03-14 01:16:04 +0100 (Fr, 14 Mrz 2008) $
// $LastChangedRevision: 4558 $
// $LastChangedBy: orbiter $
//
// LICENSE
// 
// 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., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

package de.anomic.index;

import java.io.File;
import java.io.IOException;
import java.util.Date;
import java.util.Iterator;
import java.util.List;

import de.anomic.kelondro.kelondroBLOB;
import de.anomic.kelondro.kelondroBLOBArray;
import de.anomic.kelondro.kelondroCloneableIterator;
import de.anomic.kelondro.index.Row;
import de.anomic.kelondro.index.RowSet;

public final class indexContainerBLOBArray {

    private final Row payloadrow;
    private final kelondroBLOBArray array;
    
    /**
     * open a index container based on a BLOB dump. The content of the BLOB will not be read
     * unless a .idx file exists. Only the .idx file is opened to get a fast read access to
     * the BLOB. This class provides no write methods, because BLOB files should not be
     * written in random access. To support deletion, a write access to the BLOB for deletion
     * is still possible
     * @param payloadrow
     * @param log
     * @throws IOException 
     */
    public indexContainerBLOBArray(
    		final File heapLocation,
    		final Row payloadrow) throws IOException {
        this.payloadrow = payloadrow;
        this.array = new kelondroBLOBArray(
            heapLocation,
            "index",
            payloadrow.primaryKeyLength,
            payloadrow.getOrdering(),
            0);
    }
    
    public synchronized void close() {
    	this.array.close();
    }
    
    public synchronized void clear() throws IOException {
    	this.array.clear();
    }
    
    public synchronized int size() {
        return (this.array == null) ? 0 : this.array.size();
    }
    
    public File newContainerBLOBFile() {
    	return this.array.newBLOB(new Date());
    }
    
    public void mountBLOBContainer(File location) throws IOException {
        this.array.mountBLOB(location);
    }
    
    public Row rowdef() {
        return this.payloadrow;
    }
    
    /**
     * return an iterator object that creates top-level-clones of the indexContainers
     * in the cache, so that manipulations of the iterated objects do not change
     * objects in the cache.
     * @throws IOException 
     */
    public synchronized kelondroCloneableIterator<indexContainer> wordContainers(final String startWordHash, final boolean rot) throws IOException {
        return new heapCacheIterator(startWordHash, rot);
    }

    /**
     * cache iterator: iterates objects within the heap cache. This can only be used
     * for write-enabled heaps, read-only heaps do not have a heap cache
     */
    public class heapCacheIterator implements kelondroCloneableIterator<indexContainer>, Iterable<indexContainer> {

        // this class exists, because the wCache cannot be iterated with rotation
        // and because every indexContainer Object that is iterated must be returned as top-level-clone
        // so this class simulates wCache.tailMap(startWordHash).values().iterator()
        // plus the mentioned features
        
        private final boolean rot;
        private kelondroCloneableIterator<byte[]> iterator;
        
        public heapCacheIterator(final String startWordHash, final boolean rot) throws IOException {
            this.rot = rot;
            this.iterator = array.keys(true, startWordHash.getBytes());
            // The collection's iterator will return the values in the order that their corresponding keys appear in the tree.
        }
        
        public heapCacheIterator clone(final Object secondWordHash) {
            try {
				return new heapCacheIterator((String) secondWordHash, rot);
			} catch (IOException e) {
				e.printStackTrace();
				return null;
			}
        }
        
        public boolean hasNext() {
            if (rot) return true;
            return iterator.hasNext();
        }

        public indexContainer next() {
        	try {
				if (iterator.hasNext()) {
                	return get(new String(iterator.next()));
				}
	            // rotation iteration
	            if (!rot) {
	                return null;
	            }
	            iterator = array.keys(true, null);
	            return get(new String(iterator.next()));
            } catch (IOException e) {
				e.printStackTrace();
				return null;
			}
        }

        public void remove() {
            iterator.remove();
        }

        public Iterator<indexContainer> iterator() {
            return this;
        }
        
    }

    /**
     * test if a given key is in the heap
     * this works with heaps in write- and read-mode
     * @param key
     * @return true, if the key is used in the heap; false othervise
     * @throws IOException 
     */
    public synchronized boolean has(final String key) {
        return this.array.has(key.getBytes());
    }
    
    /**
     * get a indexContainer from a heap
     * @param key
     * @return the indexContainer if one exist, null otherwise
     * @throws IOException 
     */
    public synchronized indexContainer get(final String key) throws IOException {
    	List<byte[]> entries = this.array.getAll(key.getBytes());
    	if (entries == null || entries.size() == 0) return null;
    	byte[] a = entries.remove(0);
    	indexContainer c = new indexContainer(key, RowSet.importRowSet(a, payloadrow));
    	while (entries.size() > 0) {
    		c = c.merge(new indexContainer(key, RowSet.importRowSet(entries.remove(0), payloadrow)));
    	}
    	return c;
    }
    
    /**
     * delete a indexContainer from the heap cache. This can only be used for write-enabled heaps
     * @param wordHash
     * @return the indexContainer if the cache contained the container, null othervise
     * @throws IOException 
     */
    public synchronized void delete(final String wordHash) throws IOException {
        // returns the index that had been deleted
    	array.remove(wordHash.getBytes());
    }
    
    public synchronized int replace(final String wordHash, ContainerRewriter rewriter) throws IOException {
        return array.replace(wordHash.getBytes(), new BLOBRewriter(wordHash, rewriter));
    }
    
    public class BLOBRewriter implements kelondroBLOB.Rewriter {

        ContainerRewriter rewriter;
        String wordHash;
        
        public BLOBRewriter(String wordHash, ContainerRewriter rewriter) {
            this.rewriter = rewriter;
            this.wordHash = wordHash;
        }
        
        public byte[] rewrite(byte[] b) {
            if (b == null) return null;
            indexContainer c = rewriter.rewrite(new indexContainer(this.wordHash, RowSet.importRowSet(b, payloadrow)));
            if (c == null) return null;
            return c.exportCollection();
        }
    }
/*
    public int mergeOldest() {
        if (this.array.entries() < 2) return 0;
        File f1 = this.array.unmountOldestBLOB();
        File f2 = this.array.unmountOldestBLOB();
        // iterate both files and write a new one
        new kelondroMergeIterator<indexContainer>(
                (kelondroCloneableIterator<Map.Entry<String, byte[]>>) new kelondroBLOBHeapReader.entries(f1, this.payloadrow.objectsize),
                null,
                null,
                null,
                true);
        return 0;
    }
    */
    /*
     *         new kelondroMergeIterator<indexContainer>(
                new kelondroBLOBHeapReader.entries(f1, this.payloadrow.objectsize),
                new kelondroBLOBHeapReader.entries(f2, this.payloadrow.objectsize),
                this.payloadrow.getOrdering(),
                indexContainer.containerMergeMethod,
                true);
     */
    /*
      public kelondroMergeIterator(
      final kelondroCloneableIterator<E> a,
      final kelondroCloneableIterator<E> b,
      final Comparator<E> c,
      final Method m, final boolean up) {
     */
    
    public interface ContainerRewriter {
        
        public indexContainer rewrite(indexContainer container);
        
    }

}