/**
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.jena.riot.lang ;
import java.security.MessageDigest ;
import java.security.NoSuchAlgorithmException ;
import java.util.UUID ;
import java.util.concurrent.Callable ;
import org.apache.jena.atlas.lib.Bytes ;
import org.apache.jena.atlas.lib.Cache ;
import org.apache.jena.atlas.lib.CacheFactory ;
import org.apache.jena.atlas.lib.InternalErrorException ;
import org.apache.jena.graph.Node ;
import org.apache.jena.graph.NodeFactory ;
/**
* Allocate bnode labels using a per-run seed and the label presented.
* <p>
* This is the most scalable, always legal allocator.
* <p>
* New allocators must be created per parser run, or .reset() called. These are
* fed to a digest to give a bit string, (currently MD5, to get a 128bit bit
* string) that is used to form a bNode AnonId of hex digits.
* <p>
* In addition there is a cache of label->node allocations, using the natural
* tendency to locality in a database dump. (subject bNodes, bNodes in lists
* and other data values structures like unit values).
* <p>
* Not thread safe.
*/
public class BlankNodeAllocatorHash implements BlankNodeAllocator {
private static String DigestAlgorithm = "MD5" ;
private static int CacheSize = 1000 ;
private MessageDigest mDigest ;
private byte[] seedBytes ;
// long+2 bytes to distinguish from UTF-8 bytes.
private byte[] counterBytes = new byte[10] ;
private Cache<String, Node> cache ;
private long counter = 0 ;
public BlankNodeAllocatorHash() {
reset() ;
try {
mDigest = MessageDigest.getInstance(DigestAlgorithm) ;
} catch (NoSuchAlgorithmException e) {
throw new InternalErrorException("failed to create message digest", e) ;
}
cache = CacheFactory.createCache(CacheSize) ;
}
/**
* Gets a fresh seed value
* <p>
* Note that this is called almost immediately by the constructor
* and on this initial call you will not yet have access to any
* implementation specific information used to select the seed.
* </p>
* <p>
* Implementations <strong>must</strong> return a non-null value
* so if you can't decide a seed prior to seeing your derived
* implementations constructor inputs you should return a temporary
* fake value initially. You can then call {@link #reset()} in your
* own constructor after you've taken the necessary steps that allow
* you to decide how to generate your own seed.
* </p>
* @return Seed value
*/
protected UUID freshSeed() {
return UUID.randomUUID();
}
@Override
public void reset() {
UUID seed = this.freshSeed();
seedBytes = new byte[128 / 8] ;
Bytes.setLong(seed.getMostSignificantBits(), seedBytes, 0) ;
Bytes.setLong(seed.getLeastSignificantBits(), seedBytes, 8) ;
if ( cache != null )
cache.clear();
}
@Override
public Node alloc(final String label) {
Callable<Node> getter = new Callable<Node>() {
@Override
public Node call() {
return alloc(Bytes.string2bytes(label)) ;
}
} ;
Node n = cache.getOrFill(label, getter) ;
return n ;
}
@Override
public Node create() {
counter++ ;
// Make illegal string bytes so can't clash with alloc(String)
counterBytes[0] = 0 ;
counterBytes[1] = 0 ;
Bytes.setLong(counter, counterBytes, 2) ;
return alloc(counterBytes) ;
}
private Node alloc(byte[] labelBytes) {
// ?? UUID.nameUUIDFromBytes(seedBytes+labelBytes) ;
mDigest.update(seedBytes) ;
mDigest.update(labelBytes) ;
byte[] bytes = mDigest.digest() ; // resets
String hexString = Bytes.asHexLC(bytes) ;
return NodeFactory.createBlankNode(hexString) ;
}
}