| /** |
| * 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.nio.charset.Charset; |
| import java.security.MessageDigest; |
| import java.security.NoSuchAlgorithmException; |
| |
| import org.slf4j.Logger; |
| import org.slf4j.LoggerFactory; |
| |
| /** |
| * 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 Logger LOG = LoggerFactory.getLogger(RandomSeedGenerator.class); |
| private static final Charset UTF_8 = Charset.forName("UTF-8"); |
| |
| /** 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(UTF_8)); |
| // 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; |
| } |
| } |