/**
* 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.hadoop.tools.rumen;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
/**
* The purpose of this class is to generate new random seeds from a master
* seed. This is needed to make the Random().next*() calls in rumen and mumak
* deterministic so that mumak simulations become deterministically replayable.
*
* In these tools we need many independent streams of random numbers, some of
* which are created dynamically. We seed these streams with the sub-seeds
* returned by RandomSeedGenerator.
*
* For a slightly more complicated approach to generating multiple streams of
* random numbers with better theoretical guarantees, see
* P. L'Ecuyer, R. Simard, E. J. Chen, and W. D. Kelton,
* ``An Objected-Oriented Random-Number Package with Many Long Streams and
* Substreams'', Operations Research, 50, 6 (2002), 1073--1075
* http://www.iro.umontreal.ca/~lecuyer/papers.html
* http://www.iro.umontreal.ca/~lecuyer/myftp/streams00/
*/
public class RandomSeedGenerator {
private static Log LOG = LogFactory.getLog(RandomSeedGenerator.class);
/** MD5 algorithm instance, one for each thread. */
private static final ThreadLocal<MessageDigest> md5Holder =
new ThreadLocal<MessageDigest>() {
@Override protected MessageDigest initialValue() {
MessageDigest md5 = null;
try {
md5 = MessageDigest.getInstance("MD5");
} catch (NoSuchAlgorithmException nsae) {
throw new RuntimeException("Can't create MD5 digests", nsae);
}
return md5;
}
};
/**
* Generates a new random seed.
*
* @param streamId a string identifying the stream of random numbers
* @param masterSeed higher level master random seed
* @return the random seed. Different (streamId, masterSeed) pairs result in
* (vastly) different random seeds.
*/
public static long getSeed(String streamId, long masterSeed) {
MessageDigest md5 = md5Holder.get();
md5.reset();
//'/' : make sure that we don't get the same str from ('11',0) and ('1',10)
// We could have fed the bytes of masterSeed one by one to md5.update()
// instead
String str = streamId + '/' + masterSeed;
byte[] digest = md5.digest(str.getBytes());
// Create a long from the first 8 bytes of the digest
// This is fine as MD5 has the avalanche property.
// Paranoids could have XOR folded the other 8 bytes in too.
long seed = 0;
for (int i=0; i<8; i++) {
seed = (seed<<8) + ((int)digest[i]+128);
}
return seed;
}
}