valuestore.java

这是外国一个开源推理机

/*  Sesame - Storage and Querying architecture for RDF and RDF Schema
 *  Copyright (C) 2001-2005 Aduna
 *
 *  Contact: 
 *  	Aduna
 *  	Prinses Julianaplein 14 b
 *  	3817 CS Amersfoort
 *  	The Netherlands
 *  	tel. [phone]
 *  	fax. [phone]
 *
 *  	http://aduna.biz/
 *  	http://www.openrdf.org/
 *  
 *  This library is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU Lesser General Public
 *  License as published by the Free Software Foundation; either
 *  version 2.1 of the License, or (at your option) any later version.
 *
 *  This library 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
 *  Lesser General Public License for more details.
 *
 *  You should have received a copy of the GNU Lesser General Public
 *  License along with this library; if not, write to the Free Software
 *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

package org.openrdf.sesame.sailimpl.nativerdf;

import java.io.File;
import java.io.IOException;
import java.util.Iterator;
import java.util.LinkedList;

import org.openrdf.util.ByteArrayUtil;

import org.openrdf.model.BNode;
import org.openrdf.model.Literal;
import org.openrdf.model.Resource;
import org.openrdf.model.Statement;
import org.openrdf.model.URI;
import org.openrdf.model.Value;
import org.openrdf.model.ValueFactory;
import org.openrdf.model.impl.StatementImpl;

import org.openrdf.sesame.sailimpl.nativerdf.datastore.DataStore;
import org.openrdf.sesame.sailimpl.nativerdf.model.NativeBNode;
import org.openrdf.sesame.sailimpl.nativerdf.model.NativeLiteral;
import org.openrdf.sesame.sailimpl.nativerdf.model.NativeURI;
import org.openrdf.sesame.sailimpl.nativerdf.model.NativeValue;

/**
 * Class that provides indexed storage and retrieval of RDF values.
 **/
public class ValueStore implements ValueFactory {

/*-------------+
| Constants    |
+-------------*/

	private static final String FILENAME_PREFIX = "values";
	private static final int MRU_CACHE_SIZE = 16;

	private static final byte VALUE_TYPE_MASK = 0x3; // 0000 0011
	private static final byte URI_VALUE       = 0x1; // 0000 0001
	private static final byte BNODE_VALUE     = 0x2; // 0000 0010
	private static final byte LITERAL_VALUE   = 0x3; // 0000 0011

/*-------------+
| Variables    |
+-------------*/

	private DataStore _dataStore;
	private NamespaceStore _namespaceStore;
	private NativeRdfRepository _repository;

	/** A simple cache containing the [MRU_CACHE_SIZE] most-recently used values for getValue(int id). **/
	private LinkedList _mruCache;

	/** The prefix for any new bnode IDs. **/
	private String _bnodePrefix;

	/** The ID for the next bnode that is created. **/
	private int _nextBNodeID;

/*-------------+
| Constructors |
+-------------*/

	public ValueStore(File dataDir, NamespaceStore namespaceStore, NativeRdfRepository repository)
		throws IOException
	{
		_dataStore = new DataStore(dataDir, FILENAME_PREFIX);
		_namespaceStore = namespaceStore;
		_repository = repository;

		_mruCache = new LinkedList();
		
		_updateBNodePrefix();
	}

	/**
	 * Generates a new bnode prefix based on <tt>currentTimeMillis()</tt> and
	 * resets <tt>_nextBNodeID</tt> to <tt>1</tt>.
	 **/
	private void _updateBNodePrefix() {
		// BNode prefix is based on currentTimeMillis(). Combined with a
		// sequential number per session, this gives a unique identifier.
		_bnodePrefix = "node" + Long.toString(System.currentTimeMillis(), 32) + "x";
		_nextBNodeID = 1;
	}

/*----------+
| Methods   |
+----------*/

	/**
	 * Gets the value for the specified ID.
	 *
	 * @param id A value ID.
	 * @return The value for the ID, or <tt>null</tt> no such value could be
	 * found.
	 * @exception IOException If an I/O error occurred.
	 **/
	public Value getValue(int id)
		throws IOException
	{
		NativeValue result = null;

		// Check MRU cache
		synchronized (_mruCache) {
			Iterator iter = _mruCache.iterator();
			while (iter.hasNext()) {
				NativeValue cacheValue = (NativeValue)iter.next();

				if (cacheValue.getInternalId() == id) {
					// Cache hit, move hit to most-recent position
					iter.remove();
					_mruCache.addFirst(cacheValue);

					result = cacheValue;
					break;
				}
			}
		}

		if (result == null) {
			// Value not in cache, fetch it from file
			byte[] data = _dataStore.getData(id);
			if (data != null) {
				result = _data2value(id, data);

				// Add value to MRU cache
				synchronized (_mruCache) {
					if (_mruCache.size() >= MRU_CACHE_SIZE) {
						// Cache full, remove least-recently used value
						_mruCache.removeLast();
					}
					_mruCache.addFirst(result);
				}
			}
		}

		return result;
	}

	/**
	 * Gets the ID for the specified value.
	 *
	 * @param value A value.
	 * @return The ID for the specified value, or <tt>0</tt> if no such ID could
	 * be found.
	 * @exception IOException If an I/O error occurred.
	 **/
	public int getID(Value value)
		throws IOException
	{
		return getID(value, false);
	}

	public int getID(Value value, boolean dirtyReads)
		throws IOException
	{
		boolean isOwnValue = _isOwnValue(value);
		if (isOwnValue) {
			int internalId = ((NativeValue)value).getInternalId();
			if (internalId != 0) {
				// internal ID has been set
				return internalId;
			}
		}

		int id = 0;
		byte[] data = _value2data(value, dirtyReads, false);

		if (data != null) {
			id = _dataStore.getID(data);

			if (isOwnValue) {
				// Store id in value for fast access in any consecutive calls
				((NativeValue)value).setInternalId(id);
			}
		}

		return id;
	}

	/**
	 * Starts a transaction. This prepares the ValueStore for upcoming updates
	 * to the stored data.
	 *
	 * @exception IOException If an I/O error occurred.
	 **/
	public void startTransaction()
		throws IOException
	{
		_namespaceStore.startTransaction();
		_dataStore.startTransaction();
	}

	/**
	 * Commits a transaction, applying all updates that have been performed
	 * during the transaction.
	 *
	 * @exception IOException If an I/O error occurred.
	 **/
	public void commitTransaction()
		throws IOException
	{
		_dataStore.commitTransaction();
		_namespaceStore.commitTransaction();
	}

	/**
	 * Rolls back all updates that have been performed in the current
	 * transaction and closes it.
	 *
	 * @exception IOException If an I/O error occurred.
	 **/
	public void rollbackTransaction()
		throws IOException
	{
		_dataStore.rollbackTransaction();
		_namespaceStore.rollbackTransaction();
	}

	/**
	 * Stores the supplied value and returns the ID that has been assigned to
	 * it. In case the value was already present, the value will not be stored
	 * again and the ID of the existing value is returned. This method can only
	 * be called as part of a transaction. The supplied value will not be stored
	 * until the transaction has been committed.
	 *
	 * @param value The Value to store.
	 * @return The ID that has been assigned to the value.
	 * @exception IOException If an I/O error occurred.
	 * @see #startTransaction
	 * @see #commitTransaction
	 **/
	public int storeValue(Value value)
		throws IOException
	{
		int id = 0;

		// Try to get the internal ID from the value itself
		boolean isOwnValue = _isOwnValue(value);
		if (isOwnValue) {
			id = ((NativeValue)value).getInternalId();
		}

		if (id == 0) {
			// Try to get the internal ID from a value in the MRU Cache
			synchronized (_mruCache) {
				Iterator iter = _mruCache.iterator();
				while (iter.hasNext()) {
					NativeValue cacheValue = (NativeValue)iter.next();

					if (cacheValue.equals(value)) {
						// Cache hit, move hit to most-recent position
						iter.remove();
						_mruCache.addFirst(cacheValue);

						id = cacheValue.getInternalId();
						break;
					}
				}
			}
		}

		if (id != 0) {
			// value has already been stored, increase reference count only
			_dataStore.changeReferenceCount(id, 1);
			return id;
		}

		// Unable to get internal ID in a cheap way, just store it in the data
		// store which will handle duplicates
		byte[] valueData = _value2data(value, true, true);

		id = _dataStore.storeData(valueData);