yacy_search_server/source/net/yacy/kelondro/rwi/AbstractBufferedIndex.java

// AbstractBufferedIndex.java
// -----------------------------
// (C) 2009 by Michael Peter Christen; mc@yacy.net, Frankfurt a. M., Germany
// first published 16.3.2009 on http://yacy.net
//
// This is a part of YaCy, a peer-to-peer based web search engine
//
// $LastChangedDate: 2006-04-02 22:40:07 +0200 (So, 02 Apr 2006) $
// $LastChangedRevision: 1986 $
// $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 net.yacy.kelondro.rwi;

import java.io.IOException;
import java.util.Iterator;
import java.util.TreeSet;


import net.yacy.kelondro.order.Order;


public abstract class AbstractBufferedIndex<ReferenceType extends Reference> extends AbstractIndex<ReferenceType> implements BufferedIndex<ReferenceType> {

    public AbstractBufferedIndex(final ReferenceFactory<ReferenceType> factory) {
        super(factory);
    }
    
    public synchronized TreeSet<ReferenceContainer<ReferenceType>> references(byte[] startHash, final boolean rot, int count, boolean ram) throws IOException {
        // creates a set of indexContainers
        // this does not use the cache
        final Order<ReferenceContainer<ReferenceType>> containerOrder = new ReferenceContainerOrder<ReferenceType>(factory, this.ordering().clone());
        if (startHash.length == 0) startHash = null;
        ReferenceContainer<ReferenceType> emptyContainer = ReferenceContainer.emptyContainer(factory, startHash, 0);
        containerOrder.rotate(emptyContainer);
        final TreeSet<ReferenceContainer<ReferenceType>> containers = new TreeSet<ReferenceContainer<ReferenceType>>(containerOrder);
        final Iterator<ReferenceContainer<ReferenceType>> i = references(startHash, rot, ram);
        if (ram) count = Math.min(size(), count);
        ReferenceContainer<ReferenceType> container;
        // this loop does not terminate using the i.hasNex() predicate when rot == true
        // because then the underlying iterator is a rotating iterator without termination
        // in this case a termination must be ensured with a counter
        // It must also be ensured that the counter is in/decreased every loop
        while ((count > 0) && (i.hasNext())) {
            container = i.next();
            if ((container != null) && (container.size() > 0)) {
                containers.add(container);
            }
            count--; // decrease counter even if the container was null or empty to ensure termination
        }
        return containers; // this may return less containers as demanded
    }
}